Chapter 15, Problem 1STP

Interpretation Introduction

Interpretation:The solution with the greatest number of ions needs to be determined.

Concept introduction: Electrolytes dissolve in water and get dissociated to form ions.

Number of moles of ions $=$ (concentration of the solution) $\times$ (volume of the solution in liter)

Since the number of moles of ions $\propto$ number of ions, the greater the number of moles of ions higher will be the number of ions.

Answer to Problem 1STP

Option “A” is correct.

Explanation of Solution

  $\begin{array}{c}\text{Moles of sodium phosphate}=\text{(1}{\text{.50 mol L}}^{\text{-1}}\text{)}\times \left(\text{2}\text{.0 L}\right)\\ \text{=3 mol}\end{array}$

  $\text{Sodium phosphate}$ in water dissociated as follows: ${\mathrm{Na}}_{3}P{O}_4(s)\rightleftharpoons 3{\text{Na}}^{+}(aq)+{\text{ PO}}_4^{3-}(aq)$

Total number of ions $=(3+1)=4$

Total number of moles of ions $=\left(4\times 3\right)=12$

Conclusion

  $\begin{array}{c}\text{Moles of sodium chloride}=\text{(1}{\text{.50 mol L}}^{\text{-1}}\text{)}\times \left(\text{3}\text{.0 L}\right)\\ =\text{4}\text{.5 mol}\end{array}$

Sodium chloride in water dissociated as follows: $\text{NaCl}(s)\rightleftharpoons {\text{ Na}}^{+}(aq)+{\text{ Cl}}^{-}(aq)$

Total number of ions $=\left(1+1\right)=2$

Total number of moles of ions $=\left(2\times 4.5\right)=9$

  $\begin{array}{c}\text{Moles of pottasium fluoride}=\text{(2}{\text{.0 mol L}}^{\text{-1}}\text{)}\times \left(\text{2}\text{.0 L}\right)\\ =\text{4}\text{.0 mol}\end{array}$

  $\text{Pottasium fluoride}$ in water dissociated as follows: $\text{KF}(s)\rightleftharpoons {\text{ K}}^{+}(aq)+{\text{ F}}^{-}(aq)$

Total number of ions $=\left(1+1\right)=2$

Total number of moles of ions $=\left(2\times 4.0\right)=8$

  $\begin{array}{c}\text{Moles of sodium sulfate}=\text{(3}{\text{.00 mol×L}}^{\text{-1}}\text{)}\times \left(\text{1}\text{.0 L}\right)\\ =\text{3}\text{.0 mol}\end{array}$

  $\text{Sodium sulfate}$ in water dissociated as follows: ${\text{Na}}_{\text{2}}{\text{SO}}_{\text{4}}(s)\rightleftharpoons {\text{ 2Na}}^{+}(aq)+{\text{ SO}}_4^{2-}(aq)$

Total number of ions $=\left(2+1\right)=3$

Total number of moles of ions $=\left(3\times 3.0\right)=9$

Hence, it is obvious that option B, C and D cannot be the answer.