[ctpengage]

The problem is
Consider that you had 10g of sodium hydroxide. What mass of hydrated sodium sulfate crystals (Na2SO4.7H2O).
The solution goes:
1. Calculate the amount of sodium hydroxide which is 0.25 mol.
2.Then use a balanced equation to calculate the amount of the required substance.
2NaOH+H2SO4 ---> Na2SO4+H2O
     2 mol                    1 mol
The amount of moles of Na2SO4, having figured out that the amount of sodium hydroxide is 0.25mol, is 0.125mol.
3.Then you calculate the mass of the required substance from the amount of it.
Mass of the hydrated sodium sulfate is:
0.125mol x 268.18gmol^(-1)
NB: (268.18gmol^(-1) is the molar mass of the hydrated sodium sulfate crystals (Na2SO4.7H2O)
They supply the answer as 33.52g.

I don't understand step 3. Could anyone please clarify how they accounted for the 7 water molecules in the hydrated sodium sulfate crystal when the balanced equation has a ratio of one mole of sodium sulfate to one mole of water.

[Borek]

Reaction equation describes neutralization of hydroxide, amount of water produced there doesn't matter for the molar mass of the final compound.

If you really want you can write something like:

Na₂SO₄(aq) + 7H₂O(l) -> Na₂SO₄^.7H₂O(s)

to describe crystallization, but it is not necessary - all you need is a molar mass of the Na₂SO₄^.7H₂O. Will it help if you write the formula as Na₂SH₁₄O₁₁?

[ctpengage]

i still don't get it though with the extra water molecules. where do they come from?

[Borek]

What does (l) mean? What solvent is the substance crystallized from?

[ctpengage]

thanks man. your awesome