Mastering Hydrates: A Lab Demonstration

COPPER SULFATE HYDRATE ANALYSIS [LAB]

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Summary

In this video, Stoddard Tutoring takes viewers through the process of determining the formula of a hydrate using copper sulfate as an example. The tutorial covers everything from weighing the crucible and sample to performing calculations that ascertain the number of water molecules in the compound. Through a step-by-step guide, the instructor demonstrates how heating causes water to escape as steam, leading to a change in mass. Key calculations, including molar mass determinations and mass differences, allow for the identification of the hydrate's formula: CuSO₄·6H₂O, or copper sulfate hexahydrate.

Highlights

Learn to calculate the formula of a hydrate, illustrated with copper sulfate. 🧪
Key calculations involve determining molar masses and mass differences. ⚖️
The practical steps include heating to remove water, affecting mass measurements. 🌡️
The final formula: copper sulfate hexahydrate - CuSO₄·6H₂O, is unveiled! 🎉
Harnessing periodic tables for accurate molar mass calculations is essential. 📊

Key Takeaways

Understand the process of determining the formula of a hydrate using mass calculations. 🔍
Learn the importance of precise measurements and calculations to identify chemical formulas. 📏
Discover the role of heating in driving off water from hydrates and its impact on mass. 🔥
Get familiar with common terms like anhydrous and hexahydrate for better comprehension. 📚
Appreciate the attention to detail required in lab procedures and documentation. ✍️

Overview

Ever wondered how you can determine what molecules make up a compound? In this exciting lab demo, Stoddard Tutoring walks you through this question using copper sulfate. From accurately weighing the crucible to analyzing the molecular composition, this video is your ticket to mastering hydrates! You’ll practice making mass calculations like a pro, with every step broken down in detail so you can follow with ease.

The video begins with weighing the crucible and copper sulfate, setting the stage for the scientific magic to follow. As you heat the sample, watch and learn how the blue crystals transform as water molecules evaporate into steam, leading to a decline in weight. This change marks the beginning of your journey into discovering the hydrate’s chemical formula through careful calculations.

Finally, this investigation concludes with insightful calculations using the periodic table to determine the number of waters of hydration in copper sulfate. Have fun refining your chemistry skills and watch as the mystery unveils—copper sulfate hexahydrate is the answer! Perfect for students looking to deepen their understanding of chemical experiments, this video promises both education and enjoyment.

COPPER SULFATE HYDRATE ANALYSIS [LAB] Transcription

00:00 - 00:30 this is a demonstration of how to determine the formula of a hydrate i'm going to be using copper sulfate i'll take it through the whole experiment and then i'll take it through all the calculations from very beginning to very end if you just want to watch the calculations check out the description of my video below [Music] so let's go ahead and and do things so first step you want to do is weigh your crucible and lid hopefully
00:30 - 01:00 your balance reads zero and we'll put that on there and you want to write that number uh down okay next what we will do is measure out some copper sulfate your exact procedure will tell you how many grams approximately to put into your crucible
01:00 - 01:30 this is mainly just a demonstration so i'm not too interested in reading a procedure or describing all the details or even introducing what a hydrate is you probably have a lab that describes that already so i filled this crucible about halfway up let's go ahead and weigh with the lid again you want to make sure you always weigh the lid and the crucible body
01:30 - 02:00 all right and of course the basic idea here is that we can heat this up with a flame and this will cause the water molecules that are encapsulated or entrapped in the crystal to be released and the mass should decrease as the water comes out the water that's in this crystal is actually part of the compound
02:00 - 02:30 the copper sulfate hydrate but when the water comes out it goes away as steam and into the atmosphere and so it decreases in mass and i'll position the camera right here for the duration so let's get this fired up here and again i'm not worried about the procedure and being all careful and stuff i'm just
02:30 - 03:00 lasting on this and letting it go generally a procedure will tell you to leave the lid off to enable the steam to come off freely sometimes we leave the lid on in the beginning parts of the experiment because there might be some some ejection of material as the steam passes through the solid
03:00 - 03:30 so we'll do that for a few minutes right now the crystal has kind of a characteristic dark blue color to it okay um it's been about 10 minutes and
03:30 - 04:00 i'm going to go ahead and cool this uh down to room temperature and most procedures they want you to cool this while it's covered and i just want to show you what the crystals look like um it looks a little white now in fact it might look a little pale yellow because of some sulfur that's uh possibly decomposing as i heat this too strongly so i'll now uh cool this down again we want to keep it covered because water from the atmosphere could absorb
04:00 - 04:30 back into this crystals and give us a weight increase so we want to cool it with the lid covered and i'll let that go 10 minutes and then i will come back all right we've been cooling this crucible for about
04:30 - 05:00 10 minutes and it's cool to the touch now and we'll come over here to the balance and we'll weigh it your balance should read uh zero if not hit the zero or the tear button and we'll go ahead and put that on there and take a reading there and that's it we're done with the lab i'll take you through the calculations now here's the part of the video where i take you through the calculations to calculate the formula of the hydrate so we're messing around with copper sulfate and we don't know if that's a
05:00 - 05:30 one two three four or five and basically we're trying to figure out what is n if n is three we would call the substance copper sulfate trihydrate or if n is four we would call it copper sulfate tetrahydrate uh the way we determine it is by uh mass differences and then calculating moles and going from there i'll show you all of this so uh we have the mass of the crucible which i've written that number down 22.68 grams the mass of the crucible and
05:30 - 06:00 the hydrate remember that's the copper sulfate that contains water uh molecules entrapped within the crystalline lattice that's 25.24 grams and then the mass of the crucible and the anhydrous anhydrous means without water or dry it's after we heated it and the water was removed and the mass went down about a gram to 24.23 grams so we have to do a few calculations
06:00 - 06:30 so grab a periodic table and then a calculator okay and we need to calculate some formula weights and things like that okay uh as background information the first thing you should do is calculate the molar mass of water i'm not going to go through the steps required to do this but i'm using the
06:30 - 07:00 average atomic mass uh masses from ptable.com they have some great periodic tables that you can print out on the very bottom of ptable.com you'll see a link pdf click that and you'll be able to select a periodic table you can print so 18.015
07:00 - 07:30 and then we also want to know the molar mass of copper sulfate that's without water we don't know how many water molecules are in here or how many we'll calculate really so copper is well i'm gonna do uh the four oxygens first so four times fifteen point nine nine nine add one sulfur 32.06 and
07:30 - 08:00 a copper atom weighs 63.546 atomic mass units or grams per mole so here we go 159 0.602 now i'm going to check this so the whole video is not wrong
08:00 - 08:30 great got the same answer twice all right so um that's it we're done with the periodic table not with our calculator though so let's do the steps all right so step one we want to first calculate uh the mass of water that was lost in this reaction and so uh this is the hydrate with water this is the anhydrate without water so that difference
08:30 - 09:00 is going to be you can see just by examination 1.01 grams but i'll show you the math in case your chemistry instructor really would like you to show the math now when you show the math just don't write 1.01 grams because we have different masses here we have grams of the crucible grams of water grams of copper sulfate grams of copper sulfate hydrate so write
09:00 - 09:30 h write h2o after that okay so we got grams of water and that's a substance that's involved in this chemical reaction now we want to know uh the grams of copper sulfate okay that's anhydrous so how many copper sulfate grams do we have without the water molecules okay now you can see from this entry here this is the mass of the crucible and the
09:30 - 10:00 dry salt okay the dry substance and if we subtract the mass of the crucible this difference there's no water right in this or this mass so if we subtract these two numbers we will find the mass of just the pure dry you know copper sulfate so let's do that okay so this is called step one is the mass of water step two will be the mass of copper sulfate
10:00 - 10:30 with no water and so it's going to be 24.23 grams and we want to subtract 22.68 grams okay and again show your work in case uh you're going to be graded on your ability to show work and i get 1.55 grams now i'm just using a top loading balance
10:30 - 11:00 here for this demonstration so everything's accurate out to the hundredths place okay so you want to maintain the hundredths place for all of your significant figures or your digits here okay whoops that's copper sulfate all right so i know the grams of copper sulfate i know the grams of water the next step now is to calculate moles okay because these numbers in the chemical formulas
11:00 - 11:30 the subscripts are all moles so let's calculate moles of water and we do that by dividing by the molar mass and i really like to go to town with my units here i just don't put grams or moles but i put the chemical name now because
11:30 - 12:00 we'll see a similar formula for the copper sulfate so when you're watching uh sig figs here count them up there's three sig figs here the periodic table is generally much more accurate than any reading we do in the lab so we want to whatever we get on our calculator express this as three significant figures
12:00 - 12:30 so that's moles of water remember these zeros on the left are called leading zeroes and they do not count towards the significant figures in the number so five six and one are the significant figures for this example um can you see that on the screen let me move this a little bit all right let me double check again just to make sure i don't mess up the whole youtube
12:30 - 13:00 community here 1.01 divided by 18.01 okay i'm getting the same answer twice now we want to do the same thing for moles of copper sulfate so this is the dry stuff right so this is the mass of the dry copper sulfate this is the mass the moles of the dry copper sulfate this is copper two sulfate in case you're wondering about the name
13:00 - 13:30 so uh 1.55 grams times one mole of copper two sulfate divided by um 159.602 grams of copper to sulfate
13:30 - 14:00 uh the grams of copper sulfate cancels here and we'll be left with moles so remember these zeros on the left are not significant
14:00 - 14:30 my data is accurate only to three significant figures so my final answer i round that off to three sig figs all right let's put some units on that this is mole copper sulfate okay now what we do is we calculate our ratio so we want to uh just calculate the fraction so put moles of h2o over
14:30 - 15:00 moles of copper sulfate so that would be step five this is going to be your moles of water divided by moles of the anhydrate or the anhydrous salt okay this will be your formula no matter what crazy chemical your instructor might give you whether it's copper sulfate magnesium sulfate or just some weird kind of thing so you want to
15:00 - 15:30 just take those two numbers that you calculate here and just calculate the ratio and when we do this on our calculator i'll show you what we get and then we'll round it up again and on my calculator i calculated this ratio right here to be 5.7775 etcetera okay
15:30 - 16:00 now if i want to keep three sig figs i would just write this the moles cancel so that's my um number there and the last step here would be to round this to the nearest whole number uh 5.78 is closer to six so we would round this to six so step six would be to round to a whole number
16:00 - 16:30 6. so my final answer is 6. so i can come back up to this balanced chemical equation now and i can replace i can write the the the answer to this question n is 6. i can put a 6 right here and i can put a 6 in front of here and this equation right here reads copper sulfate hexahydrate thermally decomposes or yields
16:30 - 17:00 copper two sulfate and six water molecules so the name of the substance would be copper two sulfate hexa hydrate okay uh hexa means six and so i don't have anything else to
17:00 - 17:30 discuss that's the steps and i hope you like this video please consider subscribing if you like to see this content and thanks for watching