Strong acid–strong base mixing (each 1 N): In which case will the temperature rise be the greatest, assuming equal densities and similar heat capacities?

Introduction / Context:
Heat released during neutralisation of a strong acid by a strong base is approximately constant per mole of water formed (about −57 kJ per mol at dilute conditions). The observed temperature rise depends on how many moles react and the total heat capacity of the mixed solution. This question checks the intuitive balance between reaction extent and dilution.

Given Data / Assumptions:

• Both reactants are 1 N (1 equivalent per litre).
• Density ≈ 1 g/mL and similar specific heats for solutions.
• Temperature change ΔT ∝ heat released / heat capacity of mixture.
• Heat released ∝ moles reacted = min(equivalents of acid, equivalents of base).

Concept / Approach:
For 1 N solutions, equivalents = volume (L). The limiting reagent dictates moles of water formed. The temperature rise is roughly proportional to moles reacted divided by total volume (heat capacity scales with volume). We therefore evaluate the ratio r = min(Va, Vb) / (Va + Vb) for each mixture and pick the largest r.

Step-by-Step Solution:
(a) Va = 30 mL, Vb = 30 mL → reacted = 30; total = 60 → r = 30/60 = 0.50.(b) 20 and 25 → reacted = 20; total = 45 → r ≈ 0.444.(c) 15 and 35 → reacted = 15; total = 50 → r = 0.30.(d) 35 and 15 → reacted = 15; total = 50 → r = 0.30.Highest r occurs for option (a), hence the greatest ΔT.

Verification / Alternative check:
Exact ΔT would use ΔH_neut * n_reacted divided by m * cp; with constant cp and density, the ranking by r is sufficient and matches the above conclusion.

Why Other Options Are Wrong:
They either react fewer equivalents and/or have larger total volumes, decreasing the heat-release per unit mass of solution.

Common Pitfalls:
Ignoring that the limiting reagent controls moles of water formed; focusing only on reacted moles and forgetting dilution; mixing normality with molarity without tracking equivalents.

Final Answer:
30 c.c acid and 30 c.c base