Question

Calculate the amount (g) of each of the following salts that need to be added to a 200 mL volumetric flask to produce a 2 M solution of S.

CaSO4

(NH4)2SO4

Fe2(SO4)3

Dr. BOB222,

Could you please check the following?
Thank you.

CaSO4: moles x atomic mass = .0400 x 32.066 amu = 12.8264 g
12.8264 gS x molar mass CaSO4/atomic mass S =
12.8264 g x 136.1416/32.066 =

54.45664 g

(NH4)2SO4: 12.8264 x 132.1402/32.066 (molar mass(NH4)2SO4/atomic mass S)= 52.85608 g

Fe2(SO4)3: 12.8264 x 399.8801/32.066
(molar mass Fe2(SO4)3/atomic mass S)=
159.95204 g

Thank you again.

Answer 1

I believe you are missing something here.
You want mols S = 0.200L x 2M = 0.4 mol S.
0.4mol S x (1 mol CaSO4/1 mol S) = 0.4 mol CaSO4
0.4 mol CaSO4 x molar mass CaSO4 = g CaSO4.

Answer 2

I'm confused again. Can you show me how to get the CaSO4 so I can do the other two? What did I do wrong? I showed you my work. I thought I followed your instructions from Saturday. You said I needed a number near 13. I got the 12.8264. If you could please do the CaSO4, I could probably use that as an example to finish the other two. Please help me.

Thank you.

Answer 3

I believe I read your answer as 12 and not as 55.
Your answer for a is 54.45664 and I don't see anything wrong with that except you have carried it out to more places than you are allowed. You can have 3 significant figures; I would round that to 54.5 grams.
I will check the others and try to read the right line this time.

Answer 4

b is ok except you need to round it.

Answer 5

I believe #3 is wrong. Let me show you how I would do it. Either I showed you something wrong earlier or you misunderstood somewhere along the line. At any rate, here is how to do these.
You want mols S = M x L = 2 x 0.200 = 0.400 mol S.
0.400 mol S x (1 mol CaSO4/1 mol S) = 04 mol CaSO4.
0.4 mol CaSO4 x 136.14 = 54.5 g CaSO4.

0.4 mol S x (1 mol (NH4)2SO4/1 mol S) = 0.4 mol (NH4)2SO4.
g(NH4)2SO4 = mol x molar mass = 0.400 x 132.14 = 52.9g

0.4 mol S x (1 mol Fe2(SO4)3/3 mol S) = 0.4 x 1/3 = 0.1333 mol Fe2(SO4)3
g = mols x molar mass = 0.1333 x 399.88 = 53.3g
If you know where that earlier post is give me a link. I need to look and see if I goofed. If I did perhaps I can delete my response. We don't need to keep wrong answers on the board.