Question

What happens when a solution of an acid is mixed with a solution of a base in a test tube?
(i) The temperature of the solution increases.
(ii) The temperature of the solution decreases.
(iii) The temperature of the solution remains the same.
(iv) Salt formation takes place.

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

Hint:

Every neutralization reaction between a strong acid and a strong base releases a fixed amount of heat energy, approximately \(57.3\text{ kJ/mol}\).
This exothermic nature always causes the temperature of the reaction vessel to rise.

Answer 1

The Correct Option is D

Step 1: Picture what happens when acid meets base.
Pour an acid into a base and the $H^+$ ions from the acid rush to combine with the $OH^-$ ions from the base. \[ H^+ + OH^- \to H_2O \] This bond making step is called neutralisation, and bond making always lets out energy.
Step 2: Track the leftover ions.
Once the hydrogen and hydroxide ions have paired off into water, whatever positive and negative ions remain from the original acid and base pair up too, and that pairing is exactly what we call a salt. So salt formation is guaranteed in every acid base mixing, confirming statement (iv).
Step 3: Track the heat released.
Because energy is released while the new water bonds form, that energy shows up as heat in the test tube, so if you touch the tube it feels warmer than before, confirming statement (i). Statements (ii) and (iii), a temperature drop or no change, go against this exothermic nature and are wrong.
Step 4: Conclude.
Both the temperature rise and the salt formation happen together, matching options (i) and (iv). \[ \boxed{\text{(i) and (iv)}} \]