Question

P and Q are aqueous solutions of sodium chloride and sodium hydroxide, respectively. Which of these will turn:

1. blue litmus red?
2. red litmus blue?

Answer 1

1. Neither solution will turn blue litmus red. Solution P (NaCl) is a neutral salt formed from a strong acid (HCl) and a strong base (NaOH). When dissolved in water, it dissociates into Na⁺ and Cl⁻ ions, which do not react with water. As a result, the concentration of H⁺ and OH⁻ ions in water remains equal, making the solution neutral. Solution Q (NaOH) is basic, so it won't turn blue litmus red either.
2. Sodium hydroxide solution (Q) will turn red litmus paper blue because it is a strong base and releases excess hydroxide ions (OH⁻) in water.