Question

In each of the beakers marked A, B and C, 25 mL of water was taken. Small amounts of Sodium hydroxide, anhydrous Copper sulphate and Ammonium chloride were added to beakers A, B and C respectively. Increase of temperature in breakers A and B was observed while there was a fall of temperature in beaker C. Which of the following statements are correct?

I. Changes in beakers A and B are endothermic.

II. Changes in beakers A and B are exothermic.

III. Change in beaker C is endothermic.

IV. Change in beaker C is exothermic.

• A. I and II
• B. II and III
• C. I and IV
• D. I and III

Answer 1

The correct option is B

II and III

Explanation for correct options

II. Change in beaker A: The dissolution of Sodium hydroxide $\left(\mathrm{NaOH}\right)$ in water leads to the formation of its corresponding ions $\left({\mathrm{Na}}^{+}\right)$ and $\left({\mathrm{OH}}^{-}\right)$ along with the evolution of heat.

So this reaction is an example of an exothermic reaction.

Change in beaker B: The dissolution of anhydrous Copper sulphate in water also leads to the evolution of heat along with the formation of its corresponding ions.

Thus, this reaction is also an example of exothermic change.

III. Change in beaker C: The dissolution of Ammonium chloride is an example of endothermic change.

Explanation for incorrect options

I. Changes in beakers A and B are not endothermic.

IV. Change in beaker C is not exothermic.

The correct option is Option B. II and III.