The pH of a solution of sodium hydroxide is 9. What will be its pH when this solution is diluted?
The pH of a solution of sodium hydroxide is 9. What will be its pH when this solution is diluted?
The correct option is A Less than 9
Explanation for correct answer
The pH of a solution depends on the concentration of hydrogen ions or hydroxide ions in it. The pH of acids is directly calculated from the concentration of hydrogen ions in them. To find the pH of a basic solution, the pOH of the solution is subtracted from 14. The pOH of a basic solution is inversely proportional to the concentration of hydroxide ions in it.
When a basic solution is diluted, the concentration of hydroxide ions per liter of its solution decreases. This causes an increase in the pOH of the solution. As the pOH increases, the pH of the solution decreases. Therefore, the pH of a basic solution decreases with dilution.
Therefore, when a Sodium hydroxide having pH 9 is diluted, the pH of the diluted solution will be less than 9.
Explanation for incorrect answers
Since the pH of the Sodium hydroxide solution decreases with dilution, the pH of the diluted solution cannot be 9 or greater than 9. Therefore, option (B), (C) and (D) are incorrect.
Therefore, the correct option is (A) Less than 9.
Less than 9
Explanation for correct answer
The pH of a solution depends on the concentration of hydrogen ions or hydroxide ions in it. The pH of acids is directly calculated from the concentration of hydrogen ions in them. To find the pH of a basic solution, the pOH of the solution is subtracted from 14. The pOH of a basic solution is inversely proportional to the concentration of hydroxide ions in it.
When a basic solution is diluted, the concentration of hydroxide ions per liter of its solution decreases. This causes an increase in the pOH of the solution. As the pOH increases, the pH of the solution decreases. Therefore, the pH of a basic solution decreases with dilution.
Therefore, when a Sodium hydroxide having pH 9 is diluted, the pH of the diluted solution will be less than 9.
Explanation for incorrect answers
Since the pH of the Sodium hydroxide solution decreases with dilution, the pH of the diluted solution cannot be 9 or greater than 9. Therefore, option (B), (C) and (D) are incorrect.
Therefore, the correct option is (A) Less than 9.
