Question

How would you distinguish between baking powder over washing soda by heating?

• A. Carbon dioxide is evolved in the reaction
• B. Carbon dioxide is not evolved in the reaction
• C. Hydrogen is evolved in the reaction
• D. They can be heated at high temperatures

Answer 1

Answer: (A)

Carbon dioxide is evolved in the reaction

The production of carbon dioxide is main characteristic of baking soda that makes it suitable for baking.Baking soda gives carbon dioxide and water vapour on heating at even low temperature such as ${1000}^{o}C$. The gas so formed turns lime water milky, which confirms the presence of carbon dioxide gas. When Washing soda ($N{a}_{2}C{O}_3$) is heated it does not produce carbon dioxide even at high temperature, such as ${200}^{0}C$ or ${300}^{o}C$. However sodium carbonate gives sodium oxide and carbon dioxide when heated at about ${1000}^{o}C$.

The gas produced by heating of the samples can be checked by passing through lime water. If the lime water turns milky then the evolved gas is carbon dioxide and the heated substance is baking powder.

$2NaHC{O}_3\stackrel{Heat}{\to }N{a}_{2}C{O}_3+H_{2}O+C{O}_2$

$N{a}_{2}C{O}_3.10H_{2}O\stackrel{Heat}{\to }N{a}_{2}C{O}_3+10H_{2}O$