## Homework Problem G.17

Wendy Perez 1E
Posts: 100
Joined: Sat Aug 17, 2019 12:17 am
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### Homework Problem G.17

Hi everyone!

I was having some trouble figuring out part b of homework problem G.17. The problem asks to "(b) Determine the mass of CuSO4*5H2O that must be used to prepare 250 mL of 0.20 m CuSO4(aq)."

I am not sure how I can cancel out the molar units of CuS04 and CuSO4*5H20 if they are different substances.
Last edited by Wendy Perez 1E on Thu Oct 03, 2019 12:23 am, edited 2 times in total.

Jack Riley 4f
Posts: 90
Joined: Sat Aug 24, 2019 12:17 am

### Re: Homework Problem G.17

It doesn't matter that they are different substances because the units of each are still in moles. So you need to take into account the molar mass of CuSO4.5H2O instead of just CuSO4.

Qiu Ya Wu 4I
Posts: 95
Joined: Fri Sep 20, 2019 12:17 am

### Re: Homework Problem G.17

I suggest that you view the two compounds as completely separate from one another as they have different molar masses. For part b, you can calculate the mass needed by first finding the amount of moles in CuSo4 . 5H20 and then multiplying it by its molar mass, just as you did with part a but with a different compound.

Ashley Nguyen 2L
Posts: 86
Joined: Sat Aug 17, 2019 12:18 am

### Re: Homework Problem G.17

Does anyone know if having the 5H20 on copper sulfate changes the moles of copper sulfate needed to create a .20M solution? Because we would be adding water to the solution as we add the copper sulfate, which would change the volume

Gabriella Bates 2L
Posts: 95
Joined: Thu Jul 11, 2019 12:15 am

### Re: Homework Problem G.17

Ashley Nguyen 4E wrote:Does anyone know if having the 5H20 on copper sulfate changes the moles of copper sulfate needed to create a .20M solution? Because we would be adding water to the solution as we add the copper sulfate, which would change the volume

I don't think that the moles of copper sulfate would change because it is still asking for the same concentration at the same volume. Mathematically, given that n=cV, and c and V are the same, n would also be the same. However, the hydrate means that the compound has a greater molar mass, and therefore a larger quantity would be required to get the same number of moles of copper sulfate. Then, since hydrates are present, less water would be used to fill the volumetric flask to 250 ml