A student adds dilute hydrochloric acid to a white powder and passes the evolved gas through lime water. The lime water turns milky. Which ion is most likely present in the powder?
Answer and explanation
Correct answer: Carbonate ion
Carbonate ions react with dilute HCl to release carbon dioxide: \(\mathrm{CO_3^{2-}+2H^+\rightarrow CO_2+H_2O}\). The \(\mathrm{CO_2}\) reacts with lime water, \(\mathrm{Ca(OH)_2}\), and forms an insoluble white precipitate of \(\mathrm{CaCO_3}\). This precipitate makes the lime water appear milky. Chloride, sulfate, and nitrate ions do not release \(\mathrm{CO_2}\) with dilute HCl. Exam tip: gas evolution followed by milky lime water is the standard test for a carbonate ion.
Frequently asked questions
What is the correct answer to this question?
Carbonate ion
Why is this the correct answer?
Carbonate ions react with dilute HCl to release carbon dioxide: \(\mathrm{CO_3^{2-}+2H^+\rightarrow CO_2+H_2O}\). The \(\mathrm{CO_2}\) reacts with lime water, \(\mathrm{Ca(OH)_2}\), and forms an insoluble white precipitate of \(\mathrm{CaCO_3}\). This precipitate makes the lime water appear milky. Chloride, sulfate, and nitrate ions do not release \(\mathrm{CO_2}\) with dilute HCl. Exam tip: gas evolution followed by milky lime water is the standard test for a carbonate ion.
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.
