A student is given a white solid that is known to be either sodium oxide (Na2O) or sodium peroxide (Na2O2). Which test would best distinguish between them?
Show the answer and explanation
Correct answer
B. Add dilute hydrochloric acid and test for the gas evolved.
Principle or equation
Sodium peroxide reacts with dilute acid to produce hydrogen peroxide, which can be detected, whereas sodium oxide reacts to produce only water and a salt.
Why this answer is correct
When dilute hydrochloric acid is added to sodium peroxide, oxygen gas is evolved due to decomposition of hydrogen peroxide, whereas sodium oxide gives only water and sodium chloride. The gas test (relights a glowing splint) distinguishes them.
Example
Add dilute HCl to each sample; if gas bubbles that relight a glowing splint are observed, the solid is Na2O2.
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