Question

What is the molarity of SO4^2- in a solution prepared by mixing 2.17 g of alum, KAl(SO4)2•12H2O, with 175 mL of water? The molecular weight of alum is 474.39 g/mol. Report your answer to three significant figures.

Answer 1

Answer: The concentration of sulfate ions in the solution is 0.0522 M

Explanation:

To calculate the the molarity of solution:, we use the equation:

$\text{Molarity of the solution}=\frac{\text{Mass of solute}\times 1000}{\text{Molar mass of solute}\times \text{Volume of solution (in mL)}}$

Given mass of alum = 2.17 g

Molar mass of alum = 478.39 g/mol

Volume of solution = 175 mL

Putting values in above equation, we get:

$\text{Molarity of solution}=\frac{2.17\times 1000}{474.39\times 175}\\\\\text{Molarity of solution}=0.0261M$

The chemical equation for the ionization of alum follows:

$KAl(SO_4)_2.12H_2O\rightarrow K^++Al^{3+}+2SO_4^{2-}+12H_2O$

1 mole of alum produces 1 mole of potassium ions, 1 mole of aluminium ions, 2 moles of sulfate ions and 12 moles of water

So, concentration of sulfate ions = $(2\times 0.0261)=0.0522M$

Hence, the concentration of sulfate ions in the solution is 0.0522 M