The Whole of AQA GCSE Chemistry Paper 1 | 19th May 2025

Summary

Highlights

• Start with the building blocks: atomic structure and the periodic table. 🎯
• Elements, compounds, and mixtures - what's the difference? 🤔
• Balancing equations: an essential skill for exams! 💪
• Dive into the beauty of covalent and ionic bonding. 💠
• Electrolysis: understanding the process and applications. 🔋
• Energy changes matter - grasp exothermic and endothermic reactions. ♻️
• Finesse with formulas: practice makes perfect! 📝
• Exploring nanotechnology and yields - future science! 🚀
• Titration techniques - precision is key for top marks. 🎯
• Exam ready: tips, tricks, and positive vibes! 🌟

Key Takeaways

• Master the basics of atomic structure: protons, neutrons, electrons! ⚛️
• The periodic table is your friend—know your groups and periods! 🧪
• Balance those chemical equations like a pro for maximum marks! ⚖️
• Understand the differences between ionic and covalent bonding. 🤝
• Grasp the concept of moles and practice those calculations. 📊
• Get familiar with common reactions and their products. 🔄
• Revise the setup and outcomes of electrolysis carefully. ⚡
• Don't forget energy changes and reaction types - they're key! 🔥
• Use mnemonics to remember the reactivity series and more! 🧠
• Stay calm and ace the multiple math problems expected! 🧮

Overview

Chapters

• 00:00 - 00:30: Introduction and Overview The introduction provides an overview of the essential resources and strategies for preparing for the first chemistry paper. It emphasizes a rapid coverage of topics. For thorough preparation, it suggests utilizing knowledge checklists, numerous questions, and various learning materials available for free on the website or purchasable on Amazon.
• 00:30 - 10:30: Periodic Table and Atomic Structure The chapter introduces the periodic table as a comprehensive list of all known elements, each being a single type of atom. It explains that atoms are very small, with the term 'atom' originating from Greek meaning 'uncuttable', reflecting the initial belief that atoms were the smallest possible units. The periodic table provides extensive information about the elements, though there are still many elements that have yet to be discovered.
• 10:30 - 20:30: Chemical Bonding and Equations Chemical bonding involves the combination of two or more elements that are chemically bonded together.
• 20:30 - 30:30: Properties of Substances and Materials The chapter discusses the basic properties of subatomic particles found in atoms. Protons, which reside in the nucleus of an atom, possess a mass of 1 and a positive charge of plus 1. Neutrons, also located in the nucleus, have a mass of 1 but carry no charge. Electrons, on the other hand, are situated in the outer shells of the atom and have a significantly smaller mass of 1/2000, with a negative charge of minus 1.
• 30:30 - 40:30: Chemical Reactions and Equations In the chapter titled 'Chemical Reactions and Equations,' the periodic table is explored. Each element is represented in a box containing important details: the element's name, symbol, atomic number, and mass number. The positioning of these boxes on the periodic table does not influence their information.
• 40:30 - 50:30: Electrolysis and its Applications This chapter discusses Electrolysis and its Applications. The transcript provided is incomplete but seems to touch upon atomic structure, discussing mass numbers and atomic numbers, where the atomic number indicates the number of protons and electrons in an atom, and the mass number represents the total number of protons.
• 50:30 - 65:30: Electrochemical Cells and Batteries This chapter discusses the fundamental concepts behind the structure of atoms, focusing on the constituents such as protons, neutrons, and electrons. Specifically, it uses the example of calcium to explain how to determine the number of protons, electrons, and neutrons. It explains that the atomic number represents both the number of protons and electrons, which is 20 in the case of calcium. Meanwhile, the mass number represents the total count of protons and neutrons, calculated as 40 for calcium. Therefore, by subtracting the atomic number from the mass number, one can determine the number of neutrons, which is 20.
• 65:30 - 80:30: Acids, Bases, and Salts In this chapter, the focus is on understanding how to convert verbal descriptions of chemical reactions into balanced chemical equations. Emphasis is placed on recalling the chemical symbols for various substances, using water (H2O) turning into hydrogen gas (H2) and oxygen gas (O2) as an illustrative example. The process of balancing chemical equations is also introduced, with visual techniques such as drawing lines and circling components to aid in understanding.
• 80:30 - 95:30: Endothermic and Exothermic Reactions The chapter discusses chemical reactions, specifically focusing on endothermic and exothermic reactions. It includes a demonstration of balancing chemical equations using hydrogen and oxygen as examples. The necessity of adjusting the number of elements on each side of the equation to maintain balance is emphasized. The example highlights the need to increase the number of oxygen molecules to achieve the correct balance, showcasing a practical application of the concepts.
• 95:30 - 110:30: Complex Calculations in Chemistry The chapter covers the topic of balancing chemical equations, specifically focusing on the adjustment of hydrogen and oxygen atoms to achieve balanced chemical reactions. It discusses the addition of molecules to balance the number of hydrogens and oxygens on each side of the equation. The explanation includes adding 'bubbles' to represent molecules to have 4 hydrogens and 2 oxygens, ensuring the left and right sides are equal.
• 110:30 - 120:30: Transition Metals and Nanotechnology This chapter discusses the elemental composition and chemical reactions involving hydrogen and oxygen, likely in the context of transition metals and nanotechnology. It emphasizes the importance of understanding chemical formulas, specifically referencing the formula for carbon dioxide (CO2). The speaker advises students to memorize certain chemical equations and representations, which could be vital in the study of nanotechnology and transition metals.
• 120:30 - 122:30: Conclusion and Exam Tips The chapter titled 'Conclusion and Exam Tips' appears to focus on providing a summary of key chemical compounds and elements that are essential for an exam. The transcript references chemical formulas and names such as water (H2O), oxygen gas (O2), hydrogen gas (H2), nitrogen gas (N2), ammonia (NH3), hydrochloric acid (HCl), and sulfuric acid (H2SO4). Additionally, it emphasizes the distinction between elements, which are pure substances, and compounds which are chemically bonded mixtures of two or more different elements. This summary is likely provided to aid in exam preparation by highlighting important chemical concepts and formulas.

The Whole of AQA GCSE Chemistry Paper 1 | 19th May 2025 Transcription

• 00:00 - 00:30 Hey, guys. Here is a massive summary of what you need to know for your first chemistry paper. In here, we're going to go over everything but we're only doing it quickly. If you'll make sure that you know absolutely everything, you want to get knowledge check lists, thousands of questions, links to videos, equations that you need to learn, formula you need to recall, then you can get that all for free on my website in my revision guide, or if you want to one-click order it, you can get that from Amazon.
• 00:30 - 01:00 Here we have our wonderful, beautiful periodic table. It is a list of all the elements which are known to exist. Elements are a single type of atom. An atom is a very, very small thing. The word atom is actually Greek for uncuttable. And when they named them, they thought it was the smallest thing possible. The periodic table tells us loads, and loads, and loads of information about the elements, the range of elements that are known to exist. There are still loads yet to be discovered.
• 01:00 - 01:30 A compound is two or more elements that are chemically bonded together. That's the important thing, chemically bonded together. Here, we have a structure of an atom. We have electrons that are on the shells around the outside, protons that are in the middle, and neutrons that are in the middle. And this bit in the middle here is collectively called the nucleus.
• 01:30 - 02:00 Protons are in the nucleus. They have a mass of 1 and a charge of plus 1. Neutrons are also in the nucleus. They have a mass of 1 and a charge of zero. Electrons are in the outer shells. Their mass is 1/2000 and they have a charge of minus 1.
• 02:00 - 02:30 On the periodic table, you will see lots of boxes like this. This tells you all about the elements. This is the element's name, the symbol, and there are two numbers. This is the atomic number, and this one is the mass number. Now for these, location doesn't matter.
• 02:30 - 03:00 Different textbooks, different sheets are going to put them in different locations. The larger one is the mass number, and the smaller one is the atomic number. The atomic number tells us the number of protons and the number of electrons in an atom. The mass number is the number of protons
• 03:00 - 03:30 plus the number of neutrons. So here we have calcium. The smaller number is the atomic number. The large number is the mass number. And if you want to find the number of protons, it is simply the atomic number, so in this case, 20. The number of electrons is also the atomic number, so again, 20. The neutrons is the mass number, which is 40, minus the atomic number, which is 20, equaling 20.
• 03:30 - 04:00 You need to be able to take a set of words and turn it into a balanced simple equation. So there is quite a lot for you to do here, because you need to remember the chemical symbols for quite a large number of things. Water is H2O. That turns into hydrogen gas, which is going to be H2, plus oxygen gas, which is going to be O2. And now we need to balance it. Draw a line down the middle, circle everything,
• 04:00 - 04:30 and list what we have. We have hydrogen, we have oxygen, we have hydrogen, we have oxygen. Count the number of things. 2 hydrogens, 1 oxygen, 2 hydrogens, 1 ox-- 2 oxygen, sorry. So we need to increase the number of oxygens on this side because you see there aren't enough. So we have to add another H2O. Put that in a circle, redo our numbers.
• 04:30 - 05:00 We now have 2, 4 hydrogens, and 2 oxygens. So our oxygens advance, but now our hydrogens we have more on this side than we do on this side. So we need to add more hydrogens here. Again, the only thing we can do is to add a whole other bubble. We now have 2 hydrogens here, 2 hydrogens here, making 4 in total and 2 oxygens.
• 05:00 - 05:30 So now we have 4 hydrogens on this side, 2 oxygens. 4 hydrogens and 2 oxygens. We need to rewrite that neatly for the examiner. So we have one, two bubbles of H2O turning into one, two bubbles of H2 plus 1 of O2. I seriously recommend you learn at least these formula. Carbon dioxide is CO2.
• 05:30 - 06:00 Water, H2O. Oxygen gas, O2. Hydrogen gas, H2. Nitrogen gas, N2. Ammonia, NH3. Hydrochloric acid, HCl. Sulfuric acid is H2SO4. Elements, pure things. Compounds, two or more different things chemically bonded together.
• 06:00 - 06:30 Mixture, lots of different things. Some of them chemically bonded, some of them not. When you have mixtures and you want to separate them, there are a number of different things you can do. Distillation, where you can separate things off by boiling points. The things that have a different boiling point will just stay at different temperatures. Evaporation, where we are going to remove the liquid and leave solids that have been dissolved in the liquid in the dish. Filtration, where we have large particles of solid in a liquid.
• 06:30 - 07:00 The particles that are solid will stay on the folded paper and the liquid will drip through. And fractional distillation where you can take things off at different boiling points. We haven't always known that an atom had a nucleus and electrons orbiting around the outside. We used to have a plum pudding model where we had a large cloud of positive charge with negative electrons dotted throughout, a bit like a Christmas pudding, which is why it's called the plum pudding model. Rutherford and Marsden did an experiment
• 07:00 - 07:30 to test the plum pudding model. They took an alpha particle gun, an alpha particle is positively charged, and they had a sheet of very thin gold foil. And what they did is they fired alpha particles at this sheet, and the majority of them went straight through, which was weird. Some of them got deflected a little bit, and some of them got deflected at massive amounts. And they suggested that there was
• 07:30 - 08:00 a center which was positive, a small part that was positive, and then a large section all around which was negative. And this led to the development by Bohr of the nuclear model that we use today. The model of atoms changed quite a lot over time. You don't need to know all the details of this. You need to know that Rutherford was responsible for discovering the nucleus and protons, that Chadwick discovered neutrons,
• 08:00 - 08:30 and that Bohr is our current-- or developed our current model.
• 08:30 - 09:00 The periodic table gives us loads and loads of information. The first bit of information it gives us are about groups. And the groups go down the periodic table. Group 1, group 2, 3, 4, 5, 6, 7, 8, or group zero. Groups tell us the number of electrons on the outer shell. So things in group 1 are going to have 1 electron in the outer shell. Things in group 2 are going to have 2 electrons in the outer shell. Group 6, 6 electrons in the outer shell, group 7, 7 electrons in the outer shell.
• 09:00 - 09:30 Periods go across the periodic table. So here is our first period, the one that everyone always forgets, concerning hydrogen and helium. Here is our second period. Here is our third period. And periods relate to the number of shells that things have. They also remind us how many electrons are on the-- in each shell. So in the first period, there were 2 elements, which means there are going to be 2 electrons in that shell. In the second period, there are 1, 2, 3, 4, 5, 6, 7, 8 elements, which means there are going to be
• 09:30 - 10:00 8 electrons in that shell. And we can use this information to tell us about the electronic configuration. Here, we have magnesium. Here is magnesium on the periodic table, and we can see that the number of electrons it has is 12. It is in group 2, and it is in period 3. So that tells us it has 12 electrons in total, it has 2 electrons on the outer shell, because its in group number 2, and it has 3 shells
• 10:00 - 10:30 because it is period number 3. So when we want to draw the electronic configuration of magnesium, we know it's in period 3, It's going to have 3 shells. The first thing we can do is draw 3 shells. 2, 1, 2 go on the first shell. 1, 2, 3, 4, 5, 6, 7, 8 go on the second shell. That's the most that can fit in that shell. That brings us up to 10. 10, 11, 12.
• 10:30 - 11:00 2 electrons on the outer shell. From the period, we know that the first shell can hold a maximum of 2 electrons, the second shell can hold a maximum of 8 electrons, the third shell can hold a maximum of 8 electrons, and then you only need to know up to calcium, so [INAUDIBLE].. Here, we have sodium, and it has an atomic number of 11, which means it's going to have 11 protons in the nucleus. And nuc protons have a positive charge. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11.
• 11:00 - 11:30 Now in the atom, it has 11 electrons drawn on here. Electrons have a negative charge. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 11. Now, in an atom, the positive charges and the negative charges cancel each other out, so the overall charge on the atom is going to be zero. However, when sodium makes an iron,
• 11:30 - 12:00 this electron here goes away. So it still has the same number of protons. It's still sodium. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. But it's lost an electron. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. So it has one more proton than it has an electron, meaning this is going to have an overall positive charge.
• 12:00 - 12:30 Metals are going to lose electrons, and when we lose electrons, we get positive charges. And nonmetals are going to be gaining electrons, and when we gain electrons, we get negative charges. Things in group 1 are going to lose 1 electron, so are going to be plus 1 ions. Things in group 2 are going to lose 2 electrons, so are going to be plus 2 ions.
• 12:30 - 13:00 Things in group 6, here, are going to gain 2 electrons, so are going to be minus 2 ions. And things in group 7 are going to gain 1 electron, so are going to be minus 1 ions. This beautifully colored periodic table is because there are lots of different groups, lots of different categories, on the periodic table. Group number 1, also known as alkali metals, group number 2 are the alkali earth metals, or alkaline metals,
• 13:00 - 13:30 group 7 are the halogens, and group 8 are the noble gases. The big chunk in the middle are the transition metals. Our periodic table hasn't always looked like this. The first attempt at periodic table was by Newland in the 1800s. He tried to group things into octaves and rate them by pattern, which is a really good idea, except we have oxygen and iron in the same group
• 13:30 - 14:00 and they have very different properties. He grouped them-- he arranged them by mass, but he didn't leave any gaps. And he tried to force things in to have similar patterns or properties as other things, and it didn't really work. Mendeleev was the next person to have a go. He also arranged things by mass, but the key thing is that he left gaps in his periodic table. And because he arranged things so
• 14:00 - 14:30 that they were in groups with similar patterns, and he left gaps, he could predict the properties of elements that have yet to be discovered. And he was correct in his predictions. A few years after he developed his periodic table, a couple of the elements were discovered, and they fitted in really, really, neatly, really nicely,
• 14:30 - 15:00 to his periodic table. So this table was accepted. It's changed ever so slightly by them. We now arrange things by electronic arrangement. But that's a very, very subtle difference. The group right on the far right side are group 8 or group zero. These are the noble gases. They have a full outer shell and because they have a full outer shell, they won't gain or lose any electrons which means they are really, really unreactive.
• 15:00 - 15:30 And because they are unreactive, they actually have quite a lot of uses. Helium we use in balloons, and they are also used in neon lights, as you can see here in the amazing city of Osaka. Moving over one group to group 7, we have the halogens. We are still in the nonmetals. And these are going to go around as diatomic molecules which
• 15:30 - 16:00 means their formula is going to be for chlorine gas, Cl2, fluorine gas, f2, bromine gas, Br2. They're going to go around together in pairs. Because they only want to gain 1 electron, a nice easy way for them to do that is sharing an electron with something else that is the same. So fluorine here can easily gain an extra electron by sharing it with another fluorine. They are highly reactive because they only want to get one electron.
• 16:00 - 16:30 And the most reactive ones are going to be at the top. Boiling point is going to change as we move down the group. So things that have a low boiling point or a low melting point are going to be at the top. High boiling points or high melting points are going to be at the bottom.
• 16:30 - 17:00 When they react they're going to gain an electron, meaning they're going to 4 minus 1 ions and gaining an electron is a reduction. They're going to react violently and rapidly with group 1 metals because group 1 metals want to lose 1 electrons. For example, sodium, which is soft gray metal,
• 17:00 - 17:30 will react very violently very regularly with chlorine, which is a yellow gas, to sodium chloride, which is a white powder of salt. A more reactive element will displace a less reactive element. So here we have sodium iodide reactive with bromine. Iodine is here, below bromine on the periodic table, so bromine is more reactive. So we'll displace iodine in the compound, forming sodium
• 17:30 - 18:00 bromide and iodine, whereas if you try and react bromine gas with sodium chloride, chlorine is higher than bromine on the periodic table, so it's more reactive. You are going to get no reaction because bromine cannot displace chlorine out of this. These are commonly known as displacement reactions. The halogens are mostly sterilizing things.
• 18:00 - 18:30 For example, chlorine, your commonly going to know that as from swimming pools. Halogens want to gain 1 electron, so the most reactive ones are the top. That's where there's least shielding between the electron they want to gain and the nucleus. Your alkali metals react very violently with water, and this is where you're going to see some flames coming from-- some different colors coming from. This is one of the things that we use to make the different colors in fireworks. So the lovely, lovely lilac flame from potassium,
• 18:30 - 19:00 we can use in fireworks. If you've seen these in school, these are soft, grey metals which are easily cuttable. They need to be kept in oil so it doesn't react with oxygen or with the water in the air because it's a very, very violent reaction. When the metal reacts with oxygen, we're going to get a metal oxide, which, if you've seen these in school, when it was cut, it was shiny, but [? it soon ?] started to dull. The dullness is the metal oxide. The metal plus water is going to form a metal hydroxide.
• 19:00 - 19:30 This gives it its name, it's alkali metal, because the metal hydroxide is going to be alkaline. And you can see that by the change in indicator if that's what your teacher did. And you will also notice this is a very exothermic reaction. It released a lot of heat. It also released hydrogen gas. That's what the fizzing was. The reactivity is most reactive at the bottom,
• 19:30 - 20:00 and least reactive at the top. Things at the bottom are going to have a low melting point or boiling point, and a higher melting point or boiling point at the top. Alkaline metals want to lose an electron, and the ones at the bottom are most reactive because there is more shielding between the atom-- the [INAUDIBLE] they want to use and the positive nucleus
• 20:00 - 20:30 in the middle. Solids have a very, very thick structure. Their atoms may wiggle a little bit, but it is around a fixed point. There is going to be some movement and some vibration, but they're not flowing at all, and they can't be compressed. Liquids have much more movement around, but they are not in a fixed position. They can float, but they can't be compressed. Gases are very, very free to move.
• 20:30 - 21:00 There's lots of movement going on in here. It is not around a fixed position. They do a lot of moving. They can float and they can be compressed. Going from a solid to a liquid is melting. From a liquid to a gas is evaporating. Going in this direction, we are putting energy in. Going in the other direction, energy is coming out. So from gas to a liquid, we are condensing. From a liquid to a solid, we are freezing. A compound has a melting point of 19 degrees, melting point.
• 21:00 - 21:30 And a boiling point of 74, boiling point. What is the state at room temperature? Room temperature is about 25 or 27, so when it boils, it turns from a liquid into a gas. So above there, it is going to be a gas, and below there, it is going to be a liquid. Melting point we are turning from a solid,
• 21:30 - 22:00 so this way it is going to be a solid, and above there it is going to be a liquid. So at room temperature it is going to be a liquid. Now, the other important thing to remember about boiling point and melting point is that the opposite is the same number. So boiling point is equal to condensing point. And melting point is equal to freezing point. We just took that boiling point and melting point instead of condensing point and freezing point. They are exactly the same number. So if the boiling point is 74, the condensing point is 74.
• 22:00 - 22:30 If the melting point is 19, the freezing point is 19. State symbols tell us what state something is in. So an s is a solid, l is liquid, aq is aqueous, and g is gas. If you see state symbols in an equation, the answer generally refers to them. If you see something that's liquid and liquid,
• 22:30 - 23:00 or aqueous and aqueous going to a solid, it is going to turn cloudy. If you have a liquid and a solid, or a liquid and liquid, and a gas is produced, you're going to see bubbles, or a loss of mass bubbles, or fizzing. Ionic bonding is a transfer of electrons from a metal, which is on this side of the periodic table to a nonmetal on this side of the periodic table.
• 23:00 - 23:30 Anything that is in group 1 is going to form a plus one ion. Group 2 a plus 2 ion, group 6 a minus 2 ion, group 7 a minus 1 ion. Here, we are going to make magnesium oxide. Magnesium is in group 2, so it has 2 electrons in its outer shell. Oxygen is in group 6. It has 6 electrons on its outer shell. In ionic bonding, oxygen is going to keep the electrons that it's already had,
• 23:30 - 24:00 and the electrons that were with magnesium are going to be transferred to oxygen. We call these dot-and-cross diagrams because one element has a dot for electrons and the other element has a cross for electrons. We then draw square brackets around these and indicate the charge. So magnesium has lost 2 electrons, so it's going to have a plus 2 charge. Oxygen has gained 2 electrons, so it's going to have a minus 2 charge.
• 24:00 - 24:30 Covalent bonding is the sharing of electrons between two nonmetals, these up here. And these are the common ones you need to know how to draw. For each of these, you need to be able to give the name, the formula, be able to draw it with lines, and be able to draw the dot-and-cross diagram. So hydrochloric acid or hydrogen chloride, one element of hydrogen, one element of chlorine. Ammonia and H3, nitrogen in the middle. Three hydrogens coming off around the side.
• 24:30 - 25:00 Methane, CH4, carbon in the middle, four hydrogens branching off of it. Hydrogen, H2, very simple one there. Chlorine halogens go around to diatomic molecules. Oxygen, we're getting a bit tricky now, has a double bond. Each line is equal to a pair of electrons. Here, we have two lines, that is two pairs of electrons. We need four electrons being shared in the middle. And nitrogen has a triple bond.
• 25:00 - 25:30 Two, four, six electrons being shared in the middle. If, in the exam, they give you a picture and ask you to label the formula of it, you simply need to list what we have. So in the first one, we have carbon and we have hydrogen, and then we need to count them. 1, 2, 3, 4, 5. Carbon, 5. Hydrogens, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.
• 25:30 - 26:00 The last one, carbon, hydrogen, oxygen, we have 1, 2, 3 carbons. 1, 2, 3, 4, 5 6, 7, 8 hydrogens and 1 oxygen, so we don't need to put a number after that. It's really important that you write things in the right size and in the right place, so that is incorrect because your numbers are too big.
• 26:00 - 26:30 That is incorrect because your numbers are in the wrong place. Metals are made up of positive atoms in a sea of delocalized electrons. And these electrons, being free to move, is the reason that metal can conduct electricity and why it's so good at conducting heat. An alloy looks slightly different to a metal. We still have our positive ions, we still
• 26:30 - 27:00 have our delocalized electrons, but there's something else in there as well. This may be another metal is alloyed with, or maybe something else like carbon that it is alloyed with. Pure metals have layers. Layers can slide across each other. Because they have layers and because they can slide across each other, they are soft. Alloys don't have layers, or they have distorted layers.
• 27:00 - 27:30 And the distorted layers cannot slide. And because the distorted layers cannot slide, it means they are hard. Bit of a mental break here for you guys, just a tiny pause. You are doing so, so well. Let's keep going. We are nearly there. Here, we have sodium chloride. Sodium are the grey bits you can see, and chlorine are the green bits you can see.
• 27:30 - 28:00 The blue lines are the electrostatic interactions, the electrostatic attractions, because the way we get you to draw ionic bonding is really false. It's not just one sodium combining with one chlorine. It is this massive, massive, massive lattice of sodiums and chlorines, or whatever we're looking at, bonding with everything else. So one sodium, here, isn't just going to be bonded with the chlorine and the [INAUDIBLE],, or the chlorine that it's exchanged electrons to.
• 28:00 - 28:30 It's going to be bonded with all of the other ones above it, next to it, behind it, in front of it, everything that it can reach. So this ionic bonding is a massive, massive, massive network, not just the small things that we get you to draw in class. So for ionic compounds, the structure is a giant ionic lattice.
• 28:30 - 29:00 Properties it is going to have a high melting point, high boiling point, and it is only going to conduct to a molten or dissolved.
• 29:00 - 29:30 This is because the ions need to be free to move. For simple covalent compounds such as water, carbon dioxide, oxygen, nitrogen, hydrogen gas, hydrochloric acid, or methane oxygen gas, or water, as we have here,
• 29:30 - 30:00 they are very, very small structures. They have covalent bonding. Their properties is that they have low melting points and boiling points. They're generally going to be gas at room temperature, or a liquid at room temperature.
• 30:00 - 30:30 They do not conduct electricity. For giant covalent compounds, ones made of carbon, such as graphite, diamond, or [INAUDIBLE] fullerenes, or silicon dioxide, they're going to have a giant covalent structure. Their properties are high melting and boiling points.
• 30:30 - 31:00 And they do not conduct, and they do not dissolve. Here, we have diamond. It is a giant covalent compound, or a giant covalent lattice. It is made of carbon, pure carbon.
• 31:00 - 31:30 Nothing else in there. And each carbon makes 4 bonds. So in the video, you can see that the carbon is the black bits, the covalent bonds are the red bits, and each carbon is bonded to 4 other carbons. Obviously, the ones on the [INAUDIBLE] aren't bonded to anything, but if you try and look in the middle, you can see that they are bonded to 4 other things. The properties of diamond that make it really useful
• 31:30 - 32:00 is that it is incredibly hard. It is very rare, it's hard to find, it's also very beautiful, which makes it very precious. But the main thing is that it is incredibly hard, so we can use it in drills. Graphite is also a giant covalent compound. It is like diamond, pure carbon, but each carbon
• 32:00 - 32:30 makes the 3 bonds to other carbons, not 4 like in diamond. The properties are that it is soft and it conducts electricity. Because it is in sheets, and there is a spare electron floating around in between these, that means it will conduct electricity. Graphite is what you find in pencils,
• 32:30 - 33:00 graphene is just a single sheet. If we were to compare diamond and graphite, they are both made of pure carbon. Graphite is made of 3 carbon com bonds, diamond is made of 4 carbon com bonds. Graphite is soft, diamond is hard.
• 33:00 - 33:30 Fullerenes are [? the carbon nanotubes ?] of buckminsterfullerenes, which are balls. These are, again, all made of pure carbon. They make 3 carbon bonds, but unlike graphite which is soft, these are incredibly hard. Buckminsterfullerene can be used as a lubricant in things that need lubricating, like electrical cycles,
• 33:30 - 34:00 or some parts of machines. It can be used for reinforcement, so where you need a very, very strong, very, very light things, like aircraft or bicycles. They can also both be used, or in the future be used, for drug delivery. And fullerenes, [? carbon nanotubes, ?] buckminsterfullerenes, there are loads and loads of potentials for these, but they haven't been realized yet.
• 34:00 - 34:30 With polymers, whether they have cross links or not, are going to determine what their properties are going to be like. So polymers that do have cross links are very, very fixed in place. These are going to burn upon heating, whereas polymers without cross links are going to melt upon heating because these polymers can slide across each other, whereas these ones cannot slide across each other. You can measure of the mass or volume of a reactant or product by collecting the product, say, in a gas syringe,
• 34:30 - 35:00 or using a scale or balance, to look at how the mass changes as a reaction progresses. Whenever you are measuring something, there is going to be a degree of uncertainty, whether it's a burette, a measuring cylinder, or a beaker. You need to look for the bottom of the meniscus always, because there is going to be this difference, this dip between where
• 35:00 - 35:30 it looks at the top and where it is at the bottom. And you can say whether it is on the line or in between the line, but you can never say it that accurately because it might be a quarter of the way or three quarters of the way to the next line. So while you try measuring things accurately as you can, there is always going to be a degree of uncertainty. When we are working out concentration,
• 35:30 - 36:00 that is going to be your amount divided by your volume. Concentration is measured in moles per decimeter cubed, amount is in moles and your volume is in decimeter cubed. The new style exams means are a lot of wordy questions that incorporate a lot of skills all at once. In this question, you need to first,
• 36:00 - 36:30 for all recall, the formula of things then balance the equation. So hydrochloric acid is HCl, magnesium is Mg. Now we need to work out the products and the formula of the salts. And metal plus an acid is going to give us salts plus hydrogen. Hydrogen is the easy bits.
• 36:30 - 37:00 It is H and then 2 because it goes around as a diatomic molecule. The salt is going to be magnesium chloride, but we need to know that magnesium is a 2 plus ion, and chlorine is a 1 minus ion. So it needs the MgCl2 so that there are 2 negative ions for each positive ion. Now these support you in a lot of skills, recall of the formulas and working out the sort, the product, so working out what type of equation it is,
• 37:00 - 37:30 and then after all of that, we need to balance it. So to balance our equation, we draw a line down the middle, list what we have, hydrogen chlorine, magnesium. Hydrogen, chlorine, magnesium. It is really going to help you if you keep things in the same order. Circle the compounds that we have, list the numbers of things. So we have 1 hydrogen, 1 chlorine, 1 magnesium.
• 37:30 - 38:00 2 hydrogens, 2 chlorines, 1 magnesium. So you can see, straightaway we need some more hydrogens and some more chlorines. The easiest way for us to do that is to add another HCl on there, then redoing our numbers. We have 2 hydrogens and 2 chlorines. That is balanced, writing it out neatly for the examiners, because just leaving it like this won't get you the marks. We have 2 bubbles of hydrochloric acid, plus magnesium, turns into magnesium
• 38:00 - 38:30 chloride, plus hydrogen. When you are working out the Mr, which is [INAUDIBLE],, you need to take all of the Ars, which is [INAUDIBLE] atomic masses and add them together. Now, the mass, remember, is the larger number of the two. Doesn't matter where it's located, it is the large number of the two. So hydrogen has a mass of 1, and we have 2 of them.
• 38:30 - 39:00 Silver has a mass of 32. Oxygen has a mass of 16, and we have 4 oxygens. So 1 times 2 is 2, plus 32, plus 16, times 4 which is 64, add those together, we get 98. Excellent work so far, guys. Well done. Only a little bit longer. Let's keep going. Tiny mental break, and then we can keep going.
• 39:00 - 39:30 A mole is not a rather cute, blind, black furry thing, but it is the unit for the amount of a substance. And that is going to be 6 times 10 to the 23 atoms, ions, or molecules.
• 39:30 - 40:00 And that is because that is the number of carbon atoms in 12 grams of carbon. So our equation for this is going to be moles is equal to mass over Mr. This is an incredibly complicated question which combines a lot of skills. First, we will have to work out the formula of things, work out the equation, balance the equation, and then finally, work out the amount of hydrogen peroxide.
• 40:00 - 40:30 We have hydrogen peroxide decomposing into water, H2O and oxygen gas. Now we need to balance the equation. Hydrogen, oxygen, hydrogen, oxygen, 2 hydrogens, 2 oxygens, 2 hydrogens, 3 oxygens. So we can increase that by putting more oxygens over this side, H2, O2, giving us 4 hydrogens, 4 oxygens.
• 40:30 - 41:00 Now we need some more hydrogens and oxygens over the right hand side, pop another H2 on there, and we have 4 oxygens and 4 hydrogens, giving us a final balanced equation of 2 hydrogen peroxides, making 2 water, and 1 oxygen. Now, we need to have an oxygen gas that's given off from 40.8 grams of hydrogen peroxide. The first thing we do is to work out the masses involved
• 41:00 - 41:30 in the equation. Hydrogen has a mass of 1, and there are 2 of them. Oxygen has a mass of 16, and there are 2 of them. That is 2 plus 32, giving us 34. And because there are 2 of them, that gives us a total of 68. Hydrogen is 2, 1 times 2 equals 2. Oxygen is 16, 2 plus 16 gives us 18.
• 41:30 - 42:00 18 times 2 gives us 36. And then oxygen is 16 times 2, giving us 32. So we can say that if we had 68 grams of hydrogen peroxide, it would decompose into 32 grams of oxygen, but we don't have 68 grams of hydrogen peroxide. We have 40.8 grams of hydrogen peroxide
• 42:00 - 42:30 and we need to find how much oxygen that decomposes to. This is now just a ratios question for math. I'm going to put a 1 in there. To go from 68 to 1, we need to divide by 68, so that's what I need to do on the other side as well, divide by 68, giving us naught point 47. To go from 1 to 40.8, we need to times it by 40.8, which is exactly [INAUDIBLE]
• 42:30 - 43:00 this side times 40.8. But I don't want you to clear your calculator. I want you to keep the number in your calculator. So 0.47, or the long number in the calculator and 40.8 gives us 19.2 grams. If you had cleared your calculator, and just did 0.47 times 40.8, you'd have gotten an answer of 19.176, which is close, but not the same answer.
• 43:00 - 43:30 What you've introduced is a rounding error. When you have an equation, there is always going to be a limiting reactant. And your action is going to continue using that limiting reaction forming product until you get to the point where your limiting reactant is used up. And that point, the reactant is going to stop. So whatever you don't want your limiting reactant to be, you always need to make sure the other one is in excess. There is loads and loads of maths in this,
• 43:30 - 44:00 and the majority of content of this topic and a few other bits that come out elsewhere. You can get loads and loads of practice of this in my book, Math (The Chemistry Bits). It has 60 equations for you to practice balancing, loads of titration calculations, load [INAUDIBLE] calculations, which come up later in the course, lots and lots of things for you to do. We can list the metals by how reactive they are, with the most reactive being at the top, and the least reactive being at the bottom.
• 44:00 - 44:30 Now, you need to remember these. If you have any good mnemonics remembering these, you can pop those in the description below and the comments below. That would really, really help other people. Things that are above carbon need electrolysis to be extracted, whereas things that are below carbon can just be extracted by reduction. However, things that are really, really unreactive, like silver, gold, and copper, are generally
• 44:30 - 45:00 found in the earth as their pure [INAUDIBLE],, unreacted with anything. Everything else is generally going to be reacted with oxygen in the form of metal oxides. You can also use this to predict the products from electrolysis. If the metal you are using in the electrolysis is more reactive than hydrogen, then you're going to get hydrogen as a gas.
• 45:00 - 45:30 If it is less reactive, then you're going to get something else as a gas. And we can use this to predict the products for displacement reactions. If we reacted magnesium chloride with calcium, because calcium is more reactive than the magnesium, the calcium is going to take the place. So we are going to get calcium chloride plus magnesium
• 45:30 - 46:00 as our products. However, if we reacted magnesium chloride with aluminium, because magnesium is more reactive, aluminium cannot take the place. It will not displace it, so no reaction is going to take place. And when you have a reductive action, oxidation is loss of electrons. Reduction Is gain of electrons.
• 46:00 - 46:30 A good way to remember what the electrodes are cold is that the positive electrode is the anode, and negative is cathode. At each electrode in electrolysis, we're going to have oxidation or reduction taking place and movement of electrons.
• 46:30 - 47:00 And the half equations need to reflect this, and they need to be balanced. The first thing you need to balance is the elements. In the first one, we have copper, and copper, one on each side, that's fine. Here we have a 2 plus charge. We need to make a neutral charge. The only thing we can add in is electrons, which have a negative charge. Because copper is 2 plus, we need to add in 2 electrons. We are adding in electrons, this is gain of electrons, so this is reduction.
• 47:00 - 47:30 And because copper is positive, it will go to the negative electrode, which is the cathode. The second one is a bit more complicated because you can see fluorine ion will go to a diatomic fluorine molecule. First thing we need to do is to balance the fluorines to go in there. Now we need to balance [INAUDIBLE].. We have 2 negative and it needs to go to a neutral,
• 47:30 - 48:00 so we need to lose something. The only thing we can lose are electrons, and to balance out the charges, we need to lose 2 electrons. This is loss of electrons, so it is oxidation. Fluorine is negative, so it will go to the positive electrode, and the positive electrode is the anode. You need to remember all of the equations, remember the ions, and be able to work out what is going to come from a reaction.
• 48:00 - 48:30 So if we have an acid and a metal, we are going to get a salt plus hydrogen. Acid metal oxide is going to give us a salt plus water. Acid metal hydroxide is going to be a salt plus water. Acid metal base, salt plus water. Acid plus metal carbonate is going to give us a salt, water,
• 48:30 - 49:00 and carbon dioxide. To work out the formula of the salts, you need to know the formula of all of your ions. I've made flashcards to help you with this. You can watch the video. I'm afraid you're going to need to watch it over and over again so that you learn it. And then you're going to need to make sure that you combine the ions in such a way that they are neutral overall. For making a pure salt, we are going to be making a copper sulfate.
• 49:00 - 49:30 This is mixing sulfuric acid and copper oxide to make copper sulfate and water. You're going to need to heat the sulfuric acid, stir in the copper oxide, which is a black powder, until it is in excess, which basically means you can't dissolve it anymore. Let it cool a bit, and then you can filter the solution to remove the excess copper oxide so that the black copper oxide powder will stay in the filter paper,
• 49:30 - 50:00 and then the solution of copper sulfate will come out down the bottom. Once you have your solution of copper sulfate, you can evaporate away the water to leave you with the copper sulfate crystals. Now, the size of the crystals will depend on how quickly you do this. You're going to be left with blue crystals. The blue crystals here are the hydrated ones, and the white crystals around the edge are the anhydrous ones.
• 50:00 - 50:30 On the pH scale, things that have a pH 1 are acidic, pH 7 is neutral, and 14 is an alkaline. The ion is responsible for acidity, a hydrogen ions, the ions responsibility for alkalinity are hydroxide ions. The neutralization equation is incredibly important.
• 50:30 - 51:00 It comes up a lot. And that tells us that hydrogen ions, plus hydroxide ions, can be neutralized to produce water. To carry out titration, first of all, you need to put 25 centimeter cubed in an alkali into a conical flask, add a phenolphthalein indicator, or an indicator like methyl orange, fill a burette with the acid of a known concentration, take the initial reading on the burette
• 51:00 - 51:30 and record it, and while swirling the flask, use the tap to slowly add, drop by drop, the acid into the alkaline. When the first permanent color change happens, pink to clear for phenolphthalein, stop adding the acid. Record the final volume in the burette, and repeat titres until you get it within 0.05 centimeters cubed. There are two indicators you can use for titrations, phenolphthalein, which is the one you're seeing here, which in an alkali
• 51:30 - 52:00 will be bright pink, and in an acid will be clear or colorless, or methyl orange, which in an alkali, you can see it's going this yellowy color, and in an acid will be bright red, giving us neutralization point where it is an orange color. There is a big difference between strength
• 52:00 - 52:30 and concentration. Strong acids are going to fully dissociate into hydrogen ions and other ions. The strong acids are hydrochloric acid, nitric acid, sulfuric acid, hydrobromic acid, hydroiodic acid, and chloric acid. I would expect you to know that hydrochloric acid is HCl. Nitric acid is HNO3, and sulfuric acid is H2SO4. The other ones we don't have to worry about too much.
• 52:30 - 53:00 Everything else is a weak acid, which means only partially disassociates. Here, we have strong and weak acids at high and low concentrations. So for our strong acid, we can see our hydroxide ions and our hydrogen ions are fully dissociated. They're not touching each other. They are separated. Here, we have them at a high concentration, which means there are lots of hydroxide and hydrogen ions compared to very few water molecules. Here, we have a strong acid, again fully disassociated,
• 53:00 - 53:30 but at a low concentration, meaning there aren't very many hydrogen or hydroxide ions in a lot of water. For our weak acids, they are only partially dissociated, so some of the hydrogen and hydroxide ions have separated, and some of them haven't, meaning that we are going to get some which are still together and some that are separated. At a high concentration, there are going to be lots of acid particles for a very few particles of water, whereas at a low concentration,
• 53:30 - 54:00 there aren't going to be very many acid molecules per molecule of water. Here, we have sodium chloride. Now, ionic compounds have to be molten or dissolved to be able to conduct electricity because it's when it's in its solid state you can see that this sodium and these chlorines are not going anywhere. They're very, very fixed. However, in a liquid or a molten or a dissolved state, when these ions are free to move around,
• 54:00 - 54:30 that is when they're going to be conducting electricity, and that is when you can do electrolysis. Aluminium electrolysis is a slightly different form of electrolysis. We have one electrode up here, this is our positive anode, and another electrode down here. This is our negative cathode. The molten aluminium and the cryolite-- cryolite is just a compound that is added to produce the melting point of molten aluminium oxide. It's added into this reaction vessel,
• 54:30 - 55:00 and we get one reaction taking place down here and another reaction taking place at the top. At the bottom, at the negative cathode, we are going to be attracting the positive aluminium ions. They are going to be picking up electrons and turning into aluminium atoms. This is 3 plus, so we need to pick up 3 electrons. And then at the top, at the carbon electrode, we are going to attract the negative oxygens. They are going to be losing electrons and turning
• 55:00 - 55:30 into oxygen gas because we have 2 on this side, 2 oxygens on that side, we need 2 on that side, which means we now have 4 negative charge, so we need to lose 4 electrons as well. This is a carbon electrode up here, and we are causing a-- starting a reaction which causes oxygen gas to be evolved. Eventually, the oxygen gas will react with the carbon electrode, and we are going to lose the electrode as carbon dioxide. So the carbon dioxide will wear away the electrode eventually,
• 55:30 - 56:00 so this will need to be replaced. The molten aluminium collects at the bottom and can be taken off like that, and that is how we purify aluminium. The common setups for electrolysis that you need to know are sodium chloride, sodium sulfate, copper chloride, and copper sulfate. For sodium chloride, the products you are going to get are hydrogen gas, chlorine gas, and sodium hydroxide. For copper sodium sulfate, the products you are going to get
• 56:00 - 56:30 are going to be hydrogen and oxygen gas. For copper chloride, you are going to get copper and chlorine gas. And for copper sulfate, you are going to get copper and oxygen gas. When we set up electrolysis, you need positive and negative electrode. [INAUDIBLE] there just to check that electricity is flowing. You can see bubbles collecting around the positive and negative electrode.
• 56:30 - 57:00 Sometimes this might be a metal collecting, as in the case of copper collecting here and here in copper sulfate and copper chloride. You can test for all of the different gases coming off, for example, hydrogen, chlorine, and oxygen. The test for hydrogen gas is a squeaky pop. The test for oxygen gas is relighting, glowing splint,
• 57:00 - 57:30 and the test for chlorine gas is that it bleaches damp litmus paper. An endothermic reaction feels like it gets colder, whereas an exothermic reaction, you can feel it gets hotter. Another way of saying gets colder will be to take heat in.
• 57:30 - 58:00 Another way to get hotter would be to give heat out. Now, we can make these slightly more sophisticated by replacing the word heat with the word energy. So now a sophisticated answer is that an endothermic reaction takes energy in, and an exothermic reaction gives energy out. During an endothermic reaction, energy is going to get taken in, so we have our reactants down here.
• 58:00 - 58:30 Energy gets taken in, so our product's up here. So we can say that the energy of the products is higher than the energy reactants.
• 58:30 - 59:00 During an exothermic reaction, energy reaction is given out, so our reactants, energy is given out, so our products are going to be down here, which means our products have lower energy than the reactants.
• 59:00 - 59:30 For example, an endothermic reaction will be electrolysis. An exothermic reaction would be burning or neutralization.
• 59:30 - 60:00 You need to be able to calculate the energy change when a reaction takes place, remembering that bonds energy breaking takes energy in, and bond making gives energy out. So burning hydrogen in oxygen will give out water. Calculate the energy change for this reaction. The first thing we need to do is write the balanced equation. Hydrogen, plus oxygen, gives water. We need to put a 2 there to balance out the oxygens,
• 60:00 - 60:30 and 2 there to balance out the hydrogens. Draw everything we have. So we have hydrogen and we have 2 of them, so I'm going to draw that twice, plus oxygen, turns into water. And while the examiner would probably expect you to be able to work out formulas, balance the equation, and draw them by yourself, they would not expect you to record the bonds in it.
• 60:30 - 61:00 The bond energies will be given to you in the exam. Next, we're going to list the type of bonds that we have and the number. So we have a hydrogen, hydrogen bonds, and we have 1, 2 of those. We have an oxygen, oxygen double bond, and we just have 1 double bond in there. We have oxygen hydrogen bonds, and we have 1, 2, 3, 4 of those.
• 61:00 - 61:30 And now we need to take that and multiply it by the bonds energies. So 2 bonds for hydrogen, that is 2 times 436. 1 times 498. 4 times 464. We can do the maths and work at how much is on each side adding those up. 872 plus 498 gives us 1370. There's 1856 on that side.
• 61:30 - 62:00 Now we need to do the energy of the reactions minus the energy of the product. So, 1370 minus 1856, giving us minus 486 kilojoules per mole. In this type of equation, if you got the symbol wrong, you'd probably only lose one mark. It having a negative sign in front it tells us it is exothermic.
• 62:00 - 62:30 So any reaction that is burning you can check yourself, because it should always be exothermic. We can pretty much guarantee that a big calculation is going to come up on this paper, so it is worth practicing these really well. To help you, I've written a book. The rest of this video is to separate chemistry students only. So if you have finished, well done. Excellent work. It was a bit of a slog, this video. You can go move on to the next video, use your revision guide. If you guys have chemistry, I'm afraid you've got a bit more to go.
• 62:30 - 63:00 Here, we have a simple cell with two different metals, copper and zinc, in their own solutions. So here is zinc in zinc sulfate solution and copper in copper sulfate solution. They are connected by a salt bridge, or an ion bridge, and because zinc is higher in the electrochemical series, it is going to push electrons this way, towards copper. A flow of electrons means we are going to have a potential difference. So zinc is going to be giving up electrons,
• 63:00 - 63:30 and the copper is going to be accepting electrons. That thing that we commonly refer to as a battery is actually a cell. I know, I know. It's really annoying. A cell is one battery. A battery is more than one cells. So this is a cell, and then two more of them together would be a battery. In non-rechargeable batteries, the chemical reaction that produces electricity, once they're used up,
• 63:30 - 64:00 the battery is dead, whereas in a rechargeable battery, there is a reversible reaction that goes on. So once the reactions are used up, you can pass electricity through it, which will cause the reaction to go in the opposite direction, recharging the battery. In a hydrogen fuel cell, we just have hydrogen gas reacting with oxygen gas and turning in to water.
• 64:00 - 64:30 There is a large amount of energy released, which can be used to power an electric car, and water is the only product, which means there are no carbon emissions.
• 64:30 - 65:00 There are a few problems with this, predominantly, with the production of hydrogen. At the moment, this uses fossil fuels because hydrogen [INAUDIBLE] steam with coal or natural gas, which are both fossil fuels, or hydrogen is made by electrolysis of water, but that involves electricity, which is generated using fossil fuels. The other problems are it's quite hard to find.
• 65:00 - 65:30 The hydrogen needs to be compressed, which is a problem because it would be explosive. It also needs a very, very large tank to store it in, and they don't work at low temperatures.
• 65:30 - 66:00 At the negative electrode, we are going to have hydrogen gas, minus 2 electrons, turning into hydrogen ions. At the positive electrode, we are going to have these hydrogen ions reacting with the oxygen gas and some electrons, and they are going to turn into the water.
• 66:00 - 66:30 Transition metals are in the middle. Their properties are that they are hard, shiny, and are good conductors. These are basically your traditional metals. So any property of a traditional metal, you can generally associate it with a transition metal. And because they're properties, that can be used in jewelry, in wires, or in saucepans,
• 66:30 - 67:00 and because they get all these different colors, they can be used for things like stained glass, or for coating statues. Here, the Statue of Liberty has a copper coating. Copper transitioned into compounds are generally going to be blue or bluey green. Iron 2 is light green, iron 3 is an orangey brown, a rust color.
• 67:00 - 67:30 And cobalt is a really lovely, deep, rich blue. Nanotechnology is absolutely fascinating. It is taking atoms and rearranging them into specific locations or specific sizes so that we can use it. It is much, much smaller than technology.
• 67:30 - 68:00 It is very small, but it is made up of lots of different atoms. Now, the potentials for this are massive, because as we get small, we are increasing the surface area, and when we get this small, things have very, very different properties. Things look see-through, things are flexible, things start to behave very differently to they would if they were much, much larger.
• 68:00 - 68:30 The potential for this is massive, communications, drugs delivery, personalized medicine, but people are wary about this because it is a new technology. To work out percentage yields, you need to take your actual yields and divide it by your theoretical yields.
• 68:30 - 69:00 So if this is your actual yields, then your theoretical yields is how much you thought you were going to make. To work out your atom economy, that is your Mr of atoms in the required products,
• 69:00 - 69:30 over your Mr of reactants, or the Mr of stuff you wanted, over the Mr of the stuff you actually got. For titration calculations, we first need to calculate the number of moles of acid you used.
• 69:30 - 70:00 We can use this to find the number of hydrogen ions involved in the reaction. This is going to be equal to number of hydroxide ions at the point of neutralization. You can use this to calculate the number of moles of alkali use, and concentrate the calculation of the acid. We have 25 centimeters cubed of alkali, was neutralized by 15 centimeters cubed of 0.02 moles acid. Find the concentration of the alkali. First thing I'm going to do is pull all the information out
• 70:00 - 70:30 of the question. Concentration of the alkali is what we're trying to find. Volume of the alkali, 25 centimeters cubed. Concentration of the acid, naught point 2 moles per decimeter cubed. Volume of the acid, 15 centimeters cubed. So the first thing you do is calculate the number of moles of acid used. So for the number of moles of acid used, we can use concentration of the acid times volume of the acid.
• 70:30 - 71:00 That is naught point 2, times the volume of the acid, which is 15, divided by 1,000, because we need it in decimeters cubed. So naught point 2, times naught point naught 1. Fine. Giving us an answer of naught point naught, naught, 3 moles. If we look at our balanced equation, we can see the acid
• 71:00 - 71:30 and alkali are in a 1 to 1 ratio in this equation. So there's going to be an equal number of hydrogen and hydroxide ions. So we know there are moles of an acid are 0.003 moles, which means our moles alkali must also be 0.003 moles. Now we know the number of moles of alkali, we can use concentration by volume again, or rearranging that because we know the moles and we know the volume to find the concentration. We can use moles [? equals concentration ?] [INAUDIBLE] volume again and rearranging that because we
• 71:30 - 72:00 know our moles and we know our volume, so moles divided by volume will give us concentration. So our moles from-- we've just worked out-- is 0.003. Our concentration is 25 centimeters cubed, dividing that by 1,000 to get it in decimeters cubed. So that is going to be 0.003, divided by 0.025, giving us 0.12 moles per decimeter cubed
• 72:00 - 72:30 as our concentration of alkali. When you are dealing with gases, what you need to remember is that one mole is always going to take up 24 decimeters cubed. Well done making it to the end of end of this video. You are all absolute superstars. All the best in your exams. I'm keeping all of my fingers crossed for you.