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

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Correct Answer - Option 4 : (ii) and (iv)


Enthalpy of reaction:

  • The heat of reaction is also known as the Enthalpy of reaction. It is the amount to be added or removed during a chemical reaction to keep all of the substances present at the same temperature. 
  • It is used in calculating the amount of energy per mole either released or produced in a reaction.
  • The process is exothermic if ΔH is negative and the process is endothermic if ΔH is positive.
  • The heat of formation is the amount of heat absorbed or evolved when one mole of a compound is formed from its constituent elements.


  • Neutralization reaction occurs when a solution of an acid is mixed with a solution of a base in a test tube. 
  • The result of the reaction is the production of salt and water with the evolution of heat.

NaOH (strong base) + HCl (strong acid) → ​NaCl (salt) + H2O


  • When a strong base and a weak acid reacts, the resultant is a solution with pH greater than 7, that is, basic.
  • When a strong acid reacts with a weak base, the resultant solution has a pH lesser than 7, and the solution is acidic.
  • When both are strong, the resultant solution is neutral.
  • Whatever may be the case, the ultimate combination is the combination of a proton and a hydroxyl ion to give water. The combination takes place as follows:

H+ + OH H2O

  • The combination releases heat and this heat is known as the heat of neutralization.
  • When a strong acid and a strong base react, generally the heat of neutralization is constant about -57kJ/mol.
  • When one of the components is weak, the enthalpy of neutralization decreases.
  • As the reaction releases heat or is exothermic in nature, the temperature increases and the test tube becomes hot.
  • Hence, when a solution of an acid is mixed with a solution of a base in a test tube,  the temperature of the solution increases and salt formation takes place.

Hence, the correct option is both (ii) and (iv).

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