Solutions and Colligative Properties 2 Question 15
15. Consider separate solution of $0.500 \mathrm{M} \mathrm{C}{2} \mathrm{H}{5} \mathrm{OH}(a q)$, $0.100 \mathrm{M} \mathrm{Mg}{3}\left(\mathrm{PO}{4}\right){2}(a q), 0.250 \mathrm{M} \mathrm{KBr}(a q)$ and $0.125 \mathrm{M}$ $\mathrm{Na}{3} \mathrm{PO}_{4}(a q)$ at $25^{\circ} \mathrm{C}$. Which statement is true about these solution, assuming all salts to be strong electrolytes?
(a) They all have the same osmotic pressure (2014 Main)
(b) $0.100 \mathrm{M} \mathrm{Mg}{3}\left(\mathrm{PO}{4}\right)_{2}(\mathrm{aq})$ has the highest osmotic pressure
(c) $0.125 \mathrm{M} \mathrm{Na}{3} \mathrm{PO}{4}(a q)$ has the highest osmotic pressure
(d) $0.500 \mathrm{M} \mathrm{C}{2} \mathrm{H}{5} \mathrm{OH}(a q)$ has the highest osmotic pressure
Show Answer
Solution:
- PLAN This problem includes concept of colligative properties (osmotic pressure here) and van’t Hoff factor. Calculate the effective molarity of each solution.
i.e. effective molarity $=$ van’t Hoff factor $\times$ molarity
Effective molarity $=0.5$
$$
