Question

How many total moles of ions are released when the following sample dissolves completely in water?

6.31 g of CuSO₄ ·5H₂O:

Answer 1

Molar mass of CuSO4.5H2O,

MM = 1*MM(Cu) + 1*MM(S) + 9*MM(O) + 10*MM(H)

= 1*63.55 + 1*32.07 + 9*16.0 + 10*1.008

= 249.7 g/mol

mass(CuSO4.5H2O)= 6.31 g

number of mol of CuSO4.5H2O,

n = mass of CuSO4.5H2O/molar mass of CuSO4.5H2O

=(6.31 g)/(249.7 g/mol)

= 2.527*10^-2 mol

number of molecules = number of mol * Avogadro’s number

number of molecules = 2.527*10^-2 * 6.022*10^23 molecules

number of molecules = 1.522*10^22 molecules

This is the number of molecules of CuSO4.5H2O in 6.31 g of CuSO4.5H2O

CuSO4.5H2O dissociates as:

CuSO4.5H2O —> Cu2+ + SO42- + 5 H2O

so,

1 unit of CuSO4.5H2O gives 2 ions

So,

total number of ions = 2*number of formula unit

= 2 * 1.522*10^22 molecules

= 3.044*10^22

Answer: 3.044*10^22