Qualitative analysis

Question

A saturated solution of KCl was prepared at X°C. If 30cm3 of this solution required 22.5cm3 of silver trioxonitrate (iv) solution, containing 34g in 100cm3 solution, for complete precipitation, calculate the solubility of KCl at X°C in

a)  mol/dm3

b)  g/dm3

Answer 1

KCl + AgNO3 --> KNO3 + AgCl

 

concentration of AgNO3 = 34g/(108+15+48 = 171g = molar mass of AgNO3)/0.1 litres = 340/171 M = 1.99 M

22.5 cm3 of AgNO3 solution will contain 340/171 *22.5/1000 moles = 0.045 moles. This will react will 0.045 moles of KCl according to the reaction sequence shown above. Since 0.045 moles were contained in 30 cm^3 solution, concentration in moles/liter or moles/dm^3 is 0.045/(30*0.001) = 1.5M or 1.5 moles/dm^3

To get concentration in g/dm^3, multiply this result by the molar mass of KCl, i.e. 1.5M*74g/mol = 111g/dm^3