Question E29 c.

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Athena L 1B
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Joined: Fri Sep 28, 2018 12:18 am

Question E29 c.

Postby Athena L 1B » Thu Oct 04, 2018 10:33 am

For question E29(c):

A chemist measured out 8.61 g of copper(II) chloride tetrahydrate, CuCl2 4H20.
(c) How many H20 molecules are present in the sample?

I got the other parts of the question (a,b,d) but now I'm blanking on how to go about this particular part.

julia_lok_2K
Posts: 56
Joined: Fri Sep 28, 2018 12:25 am

Re: Question E29 c.

Postby julia_lok_2K » Thu Oct 04, 2018 11:27 am

So you know how many moles of copper(II) chloride tetrahydrate you have. You multiply that number by the molar ratio of water and the molecule to get the number of moles of water. In this case, since there are 4 molecules of water in in one molecule of copper(II) chloride tetrahydrate, you would multiply by 4. Finally, since the question is asking for the number of molecules of water, you would then multiply by Avogadro's number to get the final answer.

Hope this helps!

A De Castro 14B 2H
Posts: 75
Joined: Fri Sep 28, 2018 12:29 am

Re: Question E29 c.

Postby A De Castro 14B 2H » Thu Oct 04, 2018 11:34 am

From part a of the question, you should have calculated the amount of CuCl2 4H2O in moles. Then, you can multiply that mole value by the moles of H2O in CuCl2 4H2O, which is 4. Afterwards, you can multiply that product by Avogadro's number to get the number of H2O molecules present. I've attached a picture of the calculation, if the wording doesn't make sense. Hope this helped!
Attachments
Screen Shot 2018-10-04 at 11.31.28 AM.png

Jordan_Wesson_2J
Posts: 59
Joined: Fri Sep 28, 2018 12:26 am

Re: Question E29 c.

Postby Jordan_Wesson_2J » Thu Oct 04, 2018 11:38 am

So we know from the molecular formula that we have 4 moles of H20. This means that we have to multiply 4 by the number of moles calculated in part A which was 0.42 moles. Doing this we get 0.168 moles of H2O but the question is asking how many molecules are present so we have to convert by multiplying it by 6.022x10^23. giving us 1.01x10^23 H2O molecules.


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