Question

Aluminum sulphate is used in the manufacture of paper and in the water purification industry. In the solid state, aluminum sulphate is a hydrate. The formula is Al2(SO4)3.18H2O. How many grams of sulphur are there in 0.479 moles of solid aluminum sulphate?

How many water molecules are there in a 4.63 g sample of solid aluminum sulphate?

How many moles of sulphate ions are there in a sample of solid aluminum sulphate that contains 13.7 moles of oxygen atoms?

An aqueous solution of aluminum sulphate contains 1.46 % by mass aluminum and has a density of 1.05 g/mL. What is the concentration of aluminum ions in the solution?

Answer 1

The formula is Al2(SO4)3.18H2O.

1) How many grams of sulphur are there in 0.479 moles of solid aluminum sulphate?

moles of S in aluminum sulphate = 3

moles of S in 0.479 mol aluminum sulphate = 3 x 0.479

                                                                 = 1.437 mol

mass of sulphur = 1.437 x 32 = 45.98 g

mass of sulphur = 46.0 g

2) How many water molecules are there in a 4.63 g sample of solid aluminum sulphate?

mass of aluminum sulphate = 4.63 g

moles of aluminum sulphate = 4.63 / 666.4 = 0.00695 mol

1 mol Al2(SO4)3.18H2O   --------------> 18 mol

0.00695 mol Al2(SO4)3.18H2O   -------------> ??

moles of water = 0.00695 x 18

                             = 0.125

number of water molecules = 0.125 x 6.023 x 10^23

                                                = 7.53 x 10^22

3)

How many moles of sulphate ions are there in a sample of solid aluminum sulphate that contains 13.7 moles of oxygen atoms?

1 mol Al2(SO4)3.18H2O.   ----------> 30 mol O atoms

      ?? Al2(SO4)3.18H2O.    ----------> 13.7 mol O atoms

moles of Al2(SO4)3.18H2O. = 13.7 x 1 / 30 = 0.457 mol

number of moles of sulphate ions = 0.457 x 3 = 1.37 mol

number of moles of sulphate ions = 1.37 mol

4)

Concentration = 1.46 x 10 x 1.05 / 27

                        = 0.568 M