The basic strength of sodium hydroxide solution may decrease if it is left open for a long time. What is the main reason?
Answer and explanation
Correct answer: It reacts with carbon dioxide from air
The governing concept is the reaction of a strong base with an acidic oxide. Sodium hydroxide absorbs carbon dioxide from air and reacts as 2NaOH + CO2 → Na2CO3 + H2O. Some hydroxide ions are therefore converted into carbonate, reducing the available OH− concentration and the solution’s effective basicity. Thus option A is correct; the other changes do not occur in this situation.
Frequently asked questions
What is the correct answer to this question?
It reacts with carbon dioxide from air
Why is this the correct answer?
The governing concept is the reaction of a strong base with an acidic oxide. Sodium hydroxide absorbs carbon dioxide from air and reacts as 2NaOH + CO2 → Na2CO3 + H2O. Some hydroxide ions are therefore converted into carbonate, reducing the available OH− concentration and the solution’s effective basicity. Thus option A is correct; the other changes do not occur in this situation.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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