Match each chemical solute with its characteristic solubility curve behavior in water as t… — JAMB UTME

Match each chemical solute with its characteristic solubility curve behavior in water as temperature increases.

Potassium nitrate ( $KNO_3$ )Solubility increases steeply with an increase in temperature
Sodium chloride ( $NaCl$ )Solubility remains virtually constant across temperature changes
Hydrated sodium sulfate ( $Na_2SO_4 \cdot 10H_2O$ )Solubility increases up to $32.4^\circ\text{C}$ and then continuously decreases
Calcium hydroxide ( $Ca(OH)_2$ )Solubility decreases steadily as temperature increases

Answer

Potassium nitrate (

KNO_3

) matches with steep solubility increase; Sodium chloride (

NaCl

) matches with virtually constant solubility; Hydrated sodium sulfate (

Na_2SO_4 \cdot 10H_2O

) matches with an increase up to

32.4^\circ\text{C}

followed by a decrease; Calcium hydroxide (

Ca(OH)_2

) matches with decreasing solubility.

Each salt exhibits a specific relationship between temperature and solubility governed by its enthalpy of solution and hydration state. Potassium nitrate has a steep positive curve due to endothermic dissolution. Sodium chloride shows a flat curve due to negligible heat of solution. Hydrated sodium sulfate displays a sharp break at

32.4^\circ\text{C}

marking the transition to anhydrous

Na_2SO_4

. Calcium hydroxide shows a continuous drop in solubility because its dissolution is exothermic.

Step-by-Step Solution

Analyze the thermal effect of dissolution for endothermic salts with no phase transitions.

Potassium nitrate (

KNO_3

) absorbs substantial thermal energy upon dissolving, yielding a steep positive slope on a solubility graph.

According to Le Chatelier's principle, increasing temperature shifts endothermic dissolution equilibria toward increased solute dissolution.

Evaluate salts with negligible heats of solution.

Sodium chloride (

NaCl

) exhibits a nearly horizontal curve, showing minimal change in solubility over a wide temperature range.

The lattice energy and hydration energy of

NaCl

are nearly equal, resulting in negligible temperature dependence.

Identify salts undergoing chemical dehydration or phase changes.

Glauber's salt (

Na_2SO_4 \cdot 10H_2O

) shows a sudden sharp break (kink) at

32.4^\circ\text{C}

Below

32.4^\circ\text{C}

, the decahydrate dissolves endothermically. Above

32.4^\circ\text{C}

, it dehydrates to anhydrous

Na_2SO_4

, which dissolves exothermically.

Analyze exothermic dissolution processes.

Calcium hydroxide (

Ca(OH)_2

) exhibits a downward-sloping solubility curve.

Exothermic processes release heat upon dissolution; raising the temperature suppresses dissolution and causes precipitation.

Key Concept

Effect of Temperature and Enthalpy of Solution on Solubility Curves

Estimated Time:1m 30s

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