Baking powder on heating produces carbon dioxide , which turns lime water milky. But washing soda on heating doesn\’t produce any such gas , thus, it has no effect on lime water. So, when the gas produced by heating samples can be checked by passing through lime water . If the lime water turns milky then the evolved gas is CO2 and the heated substance is baking powder.
Baking soda is one of the component of bakingpowder. Baking powder is made by the mixing of baking soda,tartric acid and starch
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Bakingsoda is used to make baking powder
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 100°C. The gas so formed turns lime water milky, which confirms the presence of carbon dioxide gas.2NaHCO3 + Heat → Na2CO3 + CO2 + H2OWhen Washing soda (Na2CO3) is heated it does not produce carbon dioxide even at high temperature, such as 200°C or 300°C. However sodium carbonate gives sodium oxide and carbon dioxide when heated at about 1000°CNa2CO3.10H2O + Heat → Na2CO3 + 10H2OThe 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.

If baking powder is heated it gives soda ash along with carbondioxide and water. If washing soda is heated its gives sodium carbonate by losing its water of crystallization, i.e by losing 10 molecules of water.