Question

A. Determine the quantity (g) of pure CaCl2 in 4.2 g of CaCl2•9H2O. Show your work.

B. Determine the quantity (g) of pure MgSO4 in 1.6 g of MgSO4•7H2O. Show your work.

Answer 1

A)

Molar mass of CaCl2.9H2O = 1*MM(Ca) + 2*MM(Cl) + 18*MM(H) + 9*MM(O)

= 1*40.08 + 2*35.45 + 18*1.008 + 9*16.0

= 273.124 g/mol

mass of CaCl2.9H2O = 4.2 g

we have below equation to be used:

number of mol of CaCl2.9H2O,

n = mass of CaCl2.9H2O/molar mass of CaCl2.9H2O

=(4.2 g)/(273.124 g/mol)

= 1.538*10^-2 mol

This should also be moles of CaCl2

Molar mass of CaCl2 = 1*MM(Ca) + 2*MM(Cl)

= 1*40.08 + 2*35.45

= 110.98 g/mol

we have below equation to be used:

mass of CaCl2,

m = number of mol * molar mass

= 1.538*10^-2 mol * 110.98 g/mol

= 1.71 g

Answer: 1.71 g

B)

Molar mass of MgSO4.7H2O = 1*MM(Mg) + 1*MM(S) + 11*MM(O) + 14*MM(H)

= 1*24.31 + 1*32.07 + 11*16.0 + 14*1.008

= 246.492 g/mol

mass of MgSO4.7H2O = 1.6 g

we have below equation to be used:

number of mol of MgSO4.7H2O,

n = mass of MgSO4.7H2O/molar mass of MgSO4.7H2O

=(1.6 g)/(246.492 g/mol)

= 6.491*10^-3 mol

This is also number of moles of MgSO4

Molar mass of MgSO4 = 1*MM(Mg) + 1*MM(S) + 4*MM(O)

= 1*24.31 + 1*32.07 + 4*16.0

= 120.38 g/mol

we have below equation to be used:

mass of MgSO4,

m = number of mol * molar mass

= 6.491*10^-3 mol * 120.38 g/mol

= 0.781 g

Answer: 0.781 g