Question

How many moles (of molecules or formula units) are in each sample?

31.45 g CF2Cl2
21.0 kg Fe (NO3) 2
0.3542 g C8H18
129 kg CaO

Answer 1

1) No of moles = mass/molar mass

given mass of CF2Cl2 = 31.45g

molar mass of CF2Cl2 = 120.913g/mol

No of moles of CF2Cl2 = 31.45g/120.913g/mol = 0.2601mol

2) given mass of Fe(NO3)2 = 21.0kg = 21000g

molar mass of Fe(NO3)2 = 179.859g/mol

No of moles of Fe(NO3)2 = 21000g/179.859g/mol = 116.76 mol

3) given mass of C8H18 = 0.3542g

molar mass of C8H18 = 114.232g/mol

No of moles of C8H18 = 0.3542g/114.232g/mol = 0.003101 mol

4) given mass of CaO = 129kg = 129000g

molar massof CaO = 40.078g/mol

no of moles of CaO = 129000g/40.078g/mol = 3219 mol