Question

Three beakers labelled as $A,B$ and $C$ each containing 25 mL of water were taken. A small amount of $NaOH$, anhydrous $CuS{O}_4$ and $NaCl$ were added to the beakers $A,B$ and $C$ respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers $A$ and $B$, whereas in case of beaker $C$, the temperature of the solution falls. Which one of the following statement(s) is(are) correct ?
(i) In beakers $A$ and $B$, exothermic process has occurred.
(ii) In beakers $A$ and $B$, endothermic process has occurred.
(iii) In beaker $C$ exothermic process has occurred.
(iv) In beaker $C$ endothermic process has occurred.

• A. (i) only
• B. (ii) only
• C. (i) and (iv)
• D. (ii) and (iii)

Answer 1

The correct option is C (i) and (iv)

$Concept:$ When heat is released $\text{(Exothermic process)}$ surrounding gets warm means temperature rises.
When heat is absorbed $\text{(Endothermic process)}$ surrounding gets cold means temperature falls.
In beaker $A$:
$NaOH+H_{2}O\to N{a}^{+}+O{H}^{-}+H_{2}O+heat$

In beaker $B$:
$CuS{O}_4\left(s\right)+5H_{2}O\left(l\right)\to CuS{O}_4.5H_{2}O\left(s\right)+heat$

Therfore in both $A$ and $B$ exothermic reactions are taking place resulting in rise in temperature.
On the other hand in beaker $C$, an endothermic reaction is taking place as heat is being absorbed, resulting in a decrease in temperature.
$NaCl+H_{2}O+heat\to N{a}^{+}+C{l}^{-}+H_{2}O$