Is the pH greater than, equal to, or less than 7 after the neutralization of each of the following pairs of acids and bases? (a) NaOH and benzoic acid (C₆H₅CO₂H)

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Identify the nature of the acid and base involved in the reaction. NaOH is a strong base, and benzoic acid (C6H5CO2H) is a weak acid.

Understand that when a strong base reacts with a weak acid, the resulting solution will be basic because the conjugate base of the weak acid will partially hydrolyze, increasing the OH- concentration.

Write the balanced chemical equation for the neutralization reaction: NaOH + C6H5CO2H \rightarrow NaC6H5CO2 + H2O.

Recognize that the product, sodium benzoate (NaC6H5CO2), is the salt formed from the reaction and can undergo hydrolysis in water to form C6H5CO2- and OH-.

Conclude that the pH of the solution will be greater than 7 due to the basic nature of the solution after the reaction.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Neutralization Reaction

A neutralization reaction occurs when an acid reacts with a base to produce water and a salt. In this process, the acidic and basic properties cancel each other out, typically resulting in a solution that is closer to neutral pH, which is 7. The specific pH of the resulting solution depends on the strength of the acid and base involved.

Strong vs. Weak Acids and Bases

Strong acids and bases completely dissociate in water, while weak acids and bases only partially dissociate. In the case of NaOH, a strong base, it fully dissociates to produce hydroxide ions. Benzoic acid, being a weak acid, does not fully dissociate, which affects the pH of the solution after neutralization.

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is considered neutral, below 7 is acidic, and above 7 is basic. The final pH after a neutralization reaction can be influenced by the relative strengths of the acid and base, determining whether the solution will be acidic, neutral, or basic.

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Textbook Question

The following pictures represent solutions of Ag2CrO4, which also may contain ions other than Ag+ and CrO42- that are not shown. Solution 1 is in equilibrium with solid Ag2CrO4. Will a precipitate of solid Ag2CrO4 form in solutions 2-4? Explain.

(1) (2) (3) (4)

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