quick gchem q

[prsndwg]

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Can someone help me understand this please:

 

[UndergradGuy7]

I think the answer is C. 5

If you get 6.4grams of CuSO4 out of 10 grams thats like saying that CuSO4 is 6.4/10 or 64% of the total mass. So (total mass)(percentage) = mass of CuSO4(which is the mass of Cu+S+4O or 159grams/mol). (x total mass) * (0.64) = 159grams of CuSO4 We find the total mass to be 249grams.

So now we know the total mass as 249grams. If there is 64% CuSO4 there must be 100-64=36% H2O. So 249 * 0.36 = 89grams. Find the answer which equals 89grams or so. 5 H2O is (18*5) = 90 grams.

 

[Questions]

please excuse my slowness.. but why did it go from 10g to 249 g? what made you do that?

 

[prsndwg]

I think the answer is C. 5

If you get 6.4grams of CuSO4 out of 10 grams thats like saying that CuSO4 is 6.4/10 or 64% of the total mass. So (total mass)(percentage) = mass of CuSO4(which is the mass of Cu+S+4O or 159grams/mol). (x total mass) * (0.64) = 159grams of CuSO4 We find the total mass to be 249grams.

So now we know the total mass as 249grams. If there is 64% CuSO4 there must be 100-64=36% H2O. So 249 * 0.36 = 89grams. Find the answer which equals 89grams or so. 5 H2O is (18*5) = 90 grams.

confused🙄

 

[UCB05]

Can someone help me understand this please:

gotta figure it out by mols.

10g CuSO4-xH2O --> 6.4g CuSO4 + 3.6g H2O

convert to mols
MM CuSO4 = (63.5 + 32 + 4x16) = 160g/mol
MM H2O = 18
6.4g CuSO4 = .04mol CuSO4
3.6g H2O = .2mol H2O

For every .04mol CuSO4 you have .2 mol H2O
For every 1mol CuSO4 you have 5 mol H2O.

x=5

 

[Questions]

thank you!

 

[prsndwg]

gotta figure it out by mols.

10g CuSO4-xH2O --> 6.4g CuSO4 + 3.6g H2O

convert to mols
MM CuSO4 = (63.5 + 32 + 4x16) = 160g/mol
MM H2O = 18
6.4g CuSO4 = .04mol CuSO4
3.6g H2O = .2mol H2O

For every .04mol CuSO4 you have .2 mol H2O
For every 1mol CuSO4 you have 5 mol H2O.

x=5

thanks