A student dissolves equal amounts of the following salts in water and measures their pH values:

Salt X: Sodium chloride (NaCl)
Salt Y: Sodium acetate (CH₃COONa)

Which of the following options correctly matches the nature of the solutions formed?

Appeared in: RRB Nsg Superintendent -29 April 2025 (Shift-1st)

Explanation

Sodium chloride (NaCl) is a salt derived from a strong acid (HCl) and a strong base (NaOH). When dissolved, its ions do not react with water, resulting in a neutral solution with a pH of approximately 7.
Sodium acetate (CH₃COONa) is a salt derived from a weak acid (acetic acid) and a strong base (NaOH). The acetate ion hydrolyzes water, producing hydroxide ions (OH⁻), which makes the solution basic with a pH greater than 7.
X - Neutral; Y - Basic matches the defining clue or classification criterion in the stem.
Supporting mechanism: The option aligns with the governing rule, pattern, sequence, classification, or exam logic being tested.
Key differentiator: It fits the one fact that separates the correct response from the closest distractor.

Option A: This option incorrectly states that a NaCl solution is acidic. Salts of strong acids and strong bases are neutral.
Option B: This option incorrectly states that a sodium acetate solution is neutral. Salts of weak acids and strong bases are basic due to hydrolysis.
Option D: This option reverses the properties of both salts. NaCl is neutral, not basic, and sodium acetate is basic, not acidic.

Visual 1: Diagram - Illustrating the hydrolysis of the acetate ion (CH₃COO⁻). The diagram would show an acetate ion reacting with a water molecule, pulling off a hydrogen ion to form acetic acid (CH₃COOH) and leaving a hydroxide ion (OH⁻), thus explaining the increase in pH.
Visual 2: Chart - A pH scale from 0 to 14. Pointers would indicate the position of the NaCl solution at pH 7 (Neutral) and the CH₃COONa solution at a pH value greater than 7 (Basic).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Salt Hydrolysis and pH of Solutions as background academic context rather than a clinical decision trigger.
Understanding the pH of solutions is fundamental for safe nursing practice, especially in the context of IV fluid administration. Isotonic saline (0.9% NaCl) has a pH close to neutral, making it compatible with blood plasma.
The body's acid-base balance is maintained by buffer systems, which often consist of a weak acid and its conjugate base (salt), similar to the acetic acid/sodium acetate pair. The bicarbonate buffer system (H₂CO₃/HCO₃⁻) is a critical example in blood.
What if? - If the question asked for the pH of ammonium chloride (NH₄Cl), the answer would be acidic. NH₄Cl is a salt of a weak base (NH₄OH) and a strong acid (HCl). The ammonium ion (NH₄⁺) would hydrolyze water to produce H⁺ ions, lowering the pH.

How to Approach the Question

Step 1: Analyze each salt to identify the parent acid and base from which it is formed.
Step 2: For Salt X (NaCl), identify the parent acid as HCl (strong acid) and the parent base as NaOH (strong base).
Step 3: Apply the rule: a salt of a strong acid and a strong base produces a neutral solution (pH ≈ 7).
Step 4: For Salt Y (CH₃COONa), identify the parent acid as CH₃COOH (weak acid) and the parent base as NaOH (strong base).
Step 5: Apply the rule: a salt of a weak acid and a strong base produces a basic solution (pH > 7) due to the hydrolysis of the anion.
Step 6: Combine the findings: X is Neutral, and Y is Basic. Select the option that matches this conclusion.

Concept Tested & Keywords

Concept Tested: Salt Hydrolysis and pH of Solutions
Stem keywords: dissolves, salts, pH values, Sodium chloride (NaCl), Sodium acetate (CH₃COONa)
Lead-in keywords: correctly matches

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Practise the full RRB Nsg Superintendent -29 April 2025 (Shift-1st)

Attempt every question from this paper in a timed mock, then review the full solution for each one.