Question

List the following aqueous solutions in order of increasing boiling point: 0.131 m C6H12O6 (glucose), 0.034 m LiBr, 0.050 m Zn(NO3)2. (The molal boiling-point-elevation constant for water is 0.51°C/m. Also, explain why?

Answer 1

The molal boiling point elevation constant for water is 0.51C/m

The increase in boiling point = i (vant hoff factor) * 0.51 * m(molality)

Vant hoff factor of glucose = 1, since it is not an ionic compound which will dissociate into ions

Hence boiling point elevation = 1 * 0.51 * 0.131

Vant hoff factor of LiBr= 2, since it is an ionic compound which will dissociate into ions

Hence boiling point elevation = 2 * 0.51 * 0.034

Vant hoff factor of Zn(NO3)2= 3, since it is an ionic compound which will dissociate into ions

Hence boiling point elevation = 3 * 0.51 * 0.050

Therefore, the correct order is

0.050 m Zn(NO3)2 > 0.131 m C6H12O6 (glucose) > 0.034 m LiBr