Question

PLEASE HELP!Suppose you begin with 1.50~g of the hydrate copper(II)sulfate · x-hydrate (CuSO4· x H2O), where x is an integer. After dehydration you find that you are left with 0.96~g of the an-hydrate CuSO4. What is the unknown integer x. Round your answer to the nearest integer, enter only an integer.

Suppose you begin with of the hydrate KAl(SO4)2 · 12H2O. After dehydration you find that you are left with 3.0~g of the an-hydrate KAl(SO4)2. How many grams did you start with? Write the value to the correct number of significance figures.

Answer 1

For first problem:
mass of water = 1.5 g - 0.96 g = 0.54 g
mole of water =
`(0.54 g)/(18 g/mole) = 0.3 mol`
mole of CuSO₄ =
`(0.96 g)/(159.6 g/mole) = 6 x 10^(-3) mol`
mole of water / mole of anhydrate =
`(0.03)/(6 x 10^(-3)) = 5`
so x equal 5

For second problem:
After dehydration 12 H₂O evaporated decreasing mass by (12 x 18) = 216 g/mole
number of moles of KAl(SO₄)₂ =
`(3)/(258.2) = 0.0116 mol`
mass of evaporated water = 216 x 0.0116 = 2.5 g
Initial weight = 2.5 g + 3 g = 5.5 g