Question

A few grams of sodium carbonate is added to \(1\ L\) of water. What is the pH or pH range of the solution?

• A. \(7-14\)
• B. \(7.0\)
• C. \(1.0\)
• D. \(1-4\)

Hint:

Salts formed from a strong base and weak acid produce basic solutions in water.

Answer 1

The Correct Option is A

Step 1: Classify the salt.
Sodium carbonate \( Na_2CO_3 \) is formed from a strong base (NaOH) and a weak acid \( (H_2CO_3) \).
Step 2: Predict the nature of the solution.
A salt of a strong base and weak acid produces a basic (alkaline) solution in water, because the anion hydrolyses to release \( OH^- \).
Step 3: Write the hydrolysis reaction.
The carbonate ion reacts with water: \[ CO_3^{2-} + H_2O \rightleftharpoons HCO_3^{-} + OH^{-} \] The production of \( OH^- \) raises the pH above 7.
Step 4: Determine the pH range.
Since the solution is basic, the pH is greater than 7. It must lie between 7 and 14.
Step 5: Eliminate the wrong options.
pH = 7 means neutral (wrong). pH 1 or 1-4 means acidic (wrong). Only the range 7-14 matches a basic solution.
Step 6: State the answer.
The pH of sodium carbonate solution lies between 7 and 14. \[ \boxed{7 \text{ to } 14} \]