Question

A student weighs out 8.21 g of (NH4)2S, transfers it to a 500. mL volumetric flask, adds enough water to dissolve the solid and then adds water to the 500 mL mark on the neck of the flask. Calculate the concentration (in molarity units) of ammonium sulfide in the resulting solution?

Answer 1

Answer: 0.24 M

Explanation:

Molarity of a solution is defined as the number of moles of solute dissolved per Liter of the solution.

$Molarity=\frac{n\times 1000}{V_s}$

where,

n= moles of solute

$Moles=\frac{\text{Given mass}}{\text{Molar mass}}=\frac{8.21g}{68.154g/mol}=0.12mole$  

$V_s$ = volume of solution  in ml = 500  ml

Putting in the values:-

$Molarity=\frac{0.12\times 1000}{500}=0.24M$

Thus the molarity of $(NH_4)_2S$ is 0.24 M.