Fundamentals G

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Hannah_1G
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Joined: Wed Sep 18, 2019 12:22 am

Fundamentals G

Postby Hannah_1G » Wed Oct 09, 2019 9:23 pm

In the second part of G.17 it asks for the mass of CuSO4 5H20 that must be used to prepare 250 mL of .2 M CuSO4(aq). I am very confused by what to do with the water molecule in this problem, I don't know how to start solving this.

Trinity Vu 1D
Posts: 53
Joined: Fri Aug 30, 2019 12:15 am

Re: Fundamentals G

Postby Trinity Vu 1D » Wed Oct 09, 2019 9:37 pm

You would need to find how many moles of CuSO4 are needed to make the .2M solution. Then using that number of moles you would multiply by the molar mass of CuSO4 5H20 instead of the molar mass of just CuSO4. From part (a) since you know that you need .05 moles of CuSO4, you'd multiply .05 by 249.68g (molar mass of CuSO4 5H2O) to get 12g CuSO4.

Emily_4B
Posts: 57
Joined: Wed Sep 18, 2019 12:21 am

Re: Fundamentals G

Postby Emily_4B » Wed Oct 09, 2019 9:37 pm

Do the same steps you did for part (a) except now use the molar mass of CuSO4•5H20, which is 249.68. So you’d have to multiply (.2 M)(0.250 L)(249.68 g/mol)=12 g of CuSO4•5H20

kevinchang_4I
Posts: 55
Joined: Tue Nov 13, 2018 12:17 am

Re: Fundamentals G

Postby kevinchang_4I » Wed Oct 09, 2019 9:43 pm

The 5H2O really is a curveball.To begin with, we need to know how many moles of CuSO4 in 250 mL of a .2 M solution. This will be .05 moles of CuSO4. This is going to be 7.98 grams CuSO4. Now we must calculate CuSO4's percent composition in CuSO4 * 5H2O. Which is molar mass CuSO4 over molar mass CuSO4 * 5H2O. We get 63.92 %. This tells us that for every 100 g of CuSO4 * 5H2O, you get 63.92g of CuSO4. If we make a conversion factor with the 7.98 grams of CuSO4 times (100 g of CuSO4 * 5H2O/63.92g of CuSO4), then we get 12.48 grams of CuSO4 needed to prepare 250 mL of .2 M CuSO4(aq).

Jialun Chen 4F
Posts: 108
Joined: Sat Sep 07, 2019 12:16 am

Re: Fundamentals G

Postby Jialun Chen 4F » Wed Oct 09, 2019 9:55 pm

I personally use the mole to mole conversion: 1 mole of CuSO4.5H2O contains 5 moles of H2O.


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