In the context of acids and bases, what happens to the $pH$ of a solution when equal concentrations of a strong acid and a strong base are mixed?

• A. The $pH$ becomes basic, above $7$.
• B. The $pH$ remains unchanged.
• C. The $pH$ becomes acidic, below $7$.
• D. The $pH$ becomes neutral, around $7$.

Answer: (D)

Verified step by step guidance

1. Understand the concept of neutralization: When a strong acid and a strong base are mixed in equal concentrations, they undergo a neutralization reaction. This means that the hydrogen ions (H⁺) from the acid react with the hydroxide ions (OH⁻) from the base to form water (H₂O).
2. Consider the properties of strong acids and bases: Strong acids completely dissociate in water to release H⁺ ions, and strong bases completely dissociate to release OH⁻ ions. This complete dissociation is crucial for the neutralization process.
3. Write the chemical equation for the neutralization reaction: For example, if hydrochloric acid (HCl) is mixed with sodium hydroxide (NaOH), the reaction is: ${H\mathrm{Cl}}_{(aq)}+{\mathrm{Na}\mathrm{OH}}_{(aq)}\to {\mathrm{Na}\mathrm{Cl}}_{(aq)}+{HO}_{(l)}$
4. Analyze the result of the reaction: The products of the neutralization reaction are water and a salt (in this case, sodium chloride, NaCl). Water is neutral with a pH of 7, and the salt does not affect the pH significantly in this context.
5. Conclude the effect on pH: Since the strong acid and strong base neutralize each other, the resulting solution is neutral, with a pH around 7. This is why the correct answer is that the pH becomes neutral, around 7.