Question

Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C, when passed through lime water, turns it milky. Identify A, B and C and hence write the molecular mass of B.

Answer 1

Hint: Baking powder ($NaHC{O_3}$ ) which is also sold for cooking, contains around 30% of bicarbonate, and various acidic ingredients which are activated by the addition of water, without the need for additional acids in the cooking medium. Many forms of baking powder contain sodium bicarbonate combined with calcium acid phosphate, sodium aluminium phosphate, or cream of tartar. Baking soda is alkaline; the acid used in baking powder avoids a metallic taste when the chemical change during baking creates sodium carbonate.

Complete step by step answer:
Salt A is the sodium bicarbonate whose molecular formula is \[NaHC{O_3}\] ​ commonly used in the bakery products, which on heating gets converted into another salt B (\[N{a_{2}}C{O_3}\] ​) which is known as the sodium carbonate.
\[2NaHC{O_3} \to N{a_2}C{O_3} + {H_2}O + C{O_{2}}\]

\[C\] is gas that is \[C{O_2}\] or carbon dioxide.

Salt B i.e. sodium carbonate is itself used for the removal of hardness of water and a gas C i.e. carbon dioxide gas is evolved.
When the gas C (\[C{O_2}\] ​) is passed over lime water, the lime water turns milky and a white precipitate,\[CaC{O_3}\] , calcium carbonate​ is formed.
Molecular mass of B, i.e. \[N{a_2}C{O_3} = \;(23 \times 2) + (12 \times 1) + (16 \times 3) = 106\;g\]

Note:
The simple definition of hardness of water is the amount of dissolved calcium and magnesium ions or compounds of these ions in the water. Hard water is high in dissolved minerals, largely calcium and magnesium. When hard water is heated, such as in a home water heater, solid deposits of calcium carbonate are formed as precipitate.