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t-raider26
08-11-10, 21:57
Alright, so we're doing this unit in Chemistry Class, and I'm kind of not understanding it at all :o I've been able to get by though. However, tonights homework... I just don't know what to do. I was wondering if any of you could help me :o

The first question is:

What is the molecular formula of the hydrate of copper (II) sulfate, CuSO4 x H2O?

So we did an expirement. First we had to weigh the empty beaker. Which weighed 116.11grams. Then we put copper (II) sulfate hydrate into the beaker, then weighed it. It weighed 119.73grams. Then we had to heat the beaker until we saw a reaction. The copper (II) sulfate is blue, but after we heated it on a hot plate, it turned grey/white. We weighed on last time after that, and it weighed 118.59grams.

Then we had a few questions to do after the experiment. Which have got me completely lost :confused:


1. Based on your observations, determine the molecular formula of CuSO4 X _H2O. (The underscore is the missing value.)


2. Suppose that you ehated a sample of a hydrated ionic compound in a test tube. What might you expect to see inside the test tube, near the mouth of the test tube? Explain.


3. Suppose that you didn't completely convert the hydrate to the anhydrous compound. Explain how this would affect:

a)the calculated percent by mass of water in the compound

b)the molecular formula you determined


4. Suppose the hydrate was heated too quickly and some of it was lost as it splattered out of the container. Explain how this would affect:

a)the calculated percent by mass of water in the compound

b)the molecular formula you determined
_______________

I know some of you will probably say I should have asked the teacher for help. But I didn't really look at the work until I got home. And it's a group assignment so I kind of need to do it or else my group will lose marks. But I will ask for some extra help tomorrow. As for now, any help would be GREATLY appreciated :o

Catapharact
09-11-10, 01:03
I only have time to help you out with question a)

Mass of Hydrate = 119.73 - 116.11 = 3.62 g

Mass of de-hydrated Cu(SO4) = 118.59 - 116.11 = 2.48g

Mass of water = 3.62 -2.48 = 1.14 g

Moles of Water = 1.14 (1/18g) = 0.063 moles

Moles of Cu(SO4) = 2.48 (1/159.6g) = 0.015 moles

Now to find the empirical formula, all you have to do is find the ratio

So inorder to find the ratio, you divide the moles of water and moles of Cu(SO4) by the lowest molar value.

So you divide 0.063 by 0.015
And you divide 0.015 by 0.015

So you get a ratio of 4:1

So your empirical formula is CuSO4.4H2O

Ward Dragon
09-11-10, 03:03
I gave it a shot, although I've been out of school for several years now so I may have gotten confused :o Only go with my answers if they make sense and go along with whatever your teacher has been saying :)

1. Based on your observations, determine the molecular formula of CuSO4 X _H2O. (The underscore is the missing value.)

I agree with Cat's calculations here.


2. Suppose that you ehated a sample of a hydrated ionic compound in a test tube. What might you expect to see inside the test tube, near the mouth of the test tube? Explain.

Hmm, I'm not really sure. Maybe water vapor or condensation? :confused: I'm thinking if the compound gets heated up and water vapor is escaping, maybe the mouth of the test tube is cooler than the bottom with the compound so the water might condense near the mouth of the test tube.


3. Suppose that you didn't completely convert the hydrate to the anhydrous compound. Explain how this would affect:

So basically what if not all of the water left the compound during the heating process and there was still some left when you took your measurements? Then when you weighed what you thought was only the compound, you were actually weighing some of the water too. That means your calculations would be wrong because the actual mass of the compound should be lower and the mass of the water should be higher.

a)the calculated percent by mass of water in the compound

If there was actually more water than you thought there was, your calculation would be low.

b)the molecular formula you determined

If there was a significantly higher percentage of water than you thought there was, then the molecular formula should have a higher coefficient for the water.

4. Suppose the hydrate was heated too quickly and some of it was lost as it splattered out of the container. Explain how this would affect:

This is basically the same question as the previous one except this time your measurement of the compound's mass is too low and therefore your calculation of the water's mass is too high.

a)the calculated percent by mass of water in the compound

This time you thought there was more water than there actually was, so your calculated percent by mass of water would be too high.

b)the molecular formula you determined

If your percent of water was too high, then your calculated coefficient for water is probably also too high.

scoopy_loopy
09-11-10, 03:13
Ugh God. I remember doing this stuff in highschool... I couldn't for the life of me go about answering it now. Good luck! :o

t-raider26
09-11-10, 11:08
OMFG! Thank you guys so much :hug: You just saved my life! I really appreciate it :D

Catapharact
09-11-10, 14:52
As much as I would like to say "you're welcome," I am getting the feeling that we have done the homework for you rather than helping you with it.

If you REALLY want to thank me, please learn the concepts and ask your teacher for help frequently.

xXhayleyroxXx
09-11-10, 14:54
As much as I would like to say "you're welcome," I am getting the feeling that we have done the homework for you rather than helping you with it.

If you REALLY want to thank me, please learn the concepts and ask your teacher for help frequently.

You only helped with question a so you hardly did all the work lol

Catapharact
09-11-10, 14:56
You only helped with question a so you hardly did all the work lol

You mean the part that ACTUALLY requires working knowledge of Empirical formulas ;)?

Not taking anything away from Ward Dragon offcourse. I know her well enough to conclude that she knows the concepts as well ;).

xXhayleyroxXx
09-11-10, 15:00
yeah you helped, but its pointless saying 'ask the teacher for help frequently' and 'learn the formulas'. When I did chemistry I asked for help all the time and tried to learn the formulas, and not for lack of trying I just couldn't do it.

Catapharact
09-11-10, 15:06
yeah you helped, but its pointless saying 'ask the teacher for help frequently' and 'learn the formulas'. When I did chemistry I asked for help all the time and tried to learn the formulas, and not for lack of trying I just couldn't do it.

Then you shouldn't have taken chemistry in High School. I don't know how the school system works in the U.K, but if its anything like Canada then you have options to choose other courses. There are plenty of alternatives to Chemistry (like Applied Science for instance.) However, I do kind of find it sad that more and more youth these days are trying to deviate from grasping the basic working knowledge of hard sciences like Chemistry and Physics.

xXhayleyroxXx
09-11-10, 15:10
Then you shouldn't have taken chemistry in High School. I don't know how the school system works in the U.K, but if its anything like Canada then you have options to choose other courses. There are plenty of alternatives to Chemistry (like Applied Science for instance.) However, I do kind of find it sad that more and more youth these days are trying to deviate from grasping the basic working knowledge of hard sciences like Chemistry and Physics.

I didn't -- we had to take it.

Catapharact
09-11-10, 15:12
I personally would prefer it that way since I want people to have a basic working knowledge of hard sciences.

xXhayleyroxXx
09-11-10, 15:16
Move to england then lol

Vlekkie
09-11-10, 15:22
Then you shouldn't have taken chemistry in High School. I don't know how the school system works in the U.K, but if its anything like Canada then you have options to choose other courses. There are plenty of alternatives to Chemistry (like Applied Science for instance.) However, I do kind of find it sad that more and more youth these days are trying to deviate from grasping the basic working knowledge of hard sciences like Chemistry and Physics.

Thats true.
However the Applied Science educations are growing here in Holland. Thanks to the NCBI/Bones/CSI/House series.
I also agree that more people should have more basic knowlegde about chemistry, maths, biology, physics.
Somethimes I help some kids with there biology & chemistry education, and i'm still surprised at how bad there knowledge is. Thanks to there eductation and somethimes teachers that teach is not there passion as the passion for the subject.

I also studying Applied Sciences > Biochemistry, but you also can study Applied Science Chemistry on our school. So you becoming a technican.

toxicraider
09-11-10, 17:08
I didn't -- we had to take it.
Yup,

It's compulsory to have at least one science GCSE (until the age of 16).

xXhayleyroxXx
09-11-10, 17:17
Yup,

It's compulsory to have at least one science GCSE (until the age of 16).

:tmb: Yeppy, I did Additional Science which had biology, chemistry and physics all included. Then I went on to do A level biology lol.

I couldn't get the hang of chemistry and physics -_-

Catapharact
09-11-10, 17:37
Thats true.
However the Applied Science educations are growing here in Holland. Thanks to the NCBI/Bones/CSI/House series.
I also agree that more people should have more basic knowlegde about chemistry, maths, biology, physics.
Somethimes I help some kids with there biology & chemistry education, and i'm still surprised at how bad there knowledge is. Thanks to there eductation and somethimes teachers that teach is not there passion as the passion for the subject.

I also studying Applied Sciences > Biochemistry, but you also can study Applied Science Chemistry on our school. So you becoming a technican.

Pretty much agree with all what you said except that I am not too fond of the fact that applied science is growing in popularity. Even biochemistry requires basic understanding of how the carbon atom works and that is no easy thing to understand (considering the fact that there is a whole discipline based on the workings of carbon, the aromatics and carbonic compounds; i.e. Organic Chemistry.)

And actually I am a business major :p. But with with added background and understanding of hard sciences, I have the privileged of working for the R&D depart. at my company. So having knowledge in various fields of study is always a good thing.

lara c. fan
09-11-10, 18:43
^I'm doing Business Studies for a GCSE... Real pity we have a teacher who really can't teach.

toxicraider
09-11-10, 19:04
:tmb: Yeppy, I did Additional Science which had biology, chemistry and physics all included. Then I went on to do A level biology lol.

I couldn't get the hang of chemistry and physics -_-
I never got into physics, :p but I'm doing the other two for A level.

xXhayleyroxXx
09-11-10, 19:39
I never got into physics, :p but I'm doing the other two for A level.

Physics is awful isn't it 0_0 We had a teacher who used to work at Sellarfield (the nuclear powerplant in Cumbria) and she hated kids. It was completely crazy having her as a teacher.
The chemistry teacher I had told me she hated me and laughed when I set my own hair alight with the bunsen burner :p

Good luck with taking them at A levels :tmb: As much as I liked Biology I found it too taxing at A level. I excell at it just the way its marked is is stupid :pi:

t-raider26
09-11-10, 19:49
Then you shouldn't have taken chemistry in High School. I don't know how the school system works in the U.K, but if its anything like Canada then you have options to choose other courses. There are plenty of alternatives to Chemistry (like Applied Science for instance.) However, I do kind of find it sad that more and more youth these days are trying to deviate from grasping the basic working knowledge of hard sciences like Chemistry and Physics.

Well I do appreciate your help. :) It's a new unit so I haven't had much experience with it yet. And this was a group project so I need to do my part or else my group would be ****ed with me. I did ask the teacher for help today and he's gonna be helping me throughout the unit.

And for the record, I took Chemistry by accident. And the course I wanted to take was full so I wasn't able to switch out.

Catapharact
09-11-10, 19:51
Well I do appreciate your help. :) It's a new unit so I haven't had much experience with it yet. And this was a group project so I need to do my part or else my group would be ****ed with me. I did ask the teacher for help today and he's gonna be helping me throughout the unit.

And for the record, I took Chemistry by accident. And the course I wanted to take was full so I wasn't able to switch out.

And I am glad I could help so long as you keep on taking the required help you need to understand the unit :). Its not a difficult concept to grasp once you get the jist of it. The calculations can get tedious at times which is why its always good to do the entire process step by step. That way, you can go back and fix things easily if you get the wrong answer.