a sample of hydrated NiSO4 witha mass of 4.414g is heated to remove all water crystallisation. The resultant mass is 2.287g. How many H2O molecules to each NiSO4 were there in the original sample

Mr of NiSO4 is 154.8 g/mol Mr of H2O is 18

Mass of NiSO4 in sample is 2.287 g Mass of H2O in sample is 4.414-2.287 = 2.127g

divide mass of each of NiSO4 and H2O by Mr to obtain the ratio in moles

NiSO4: 2.287 / 154.8 = 0.0148 mol H2O: 2.127 / 18 = 0.118 mol

therefore there are 7.98 H2O to each NiSO4 -> 8 H2O to each NiSO4