Question

What is the action of heat on the following compound?
i.$N{a_{{\text{2}}}}C{O_3}{\text{ }}$ and $CaC{O_3}$ ​
ii.$MgC{l_2}.6{H_2}O$ and $CaC{l_2}.6{H_{2}}O$
iii.$Ca{(N{O_3})_2}$ and $NaN{O_2}$

Answer 1

We can solve these questions by understanding the effect of heat on different compounds. Carbonates on heating will give out carbon dioxide. Hydrated salts on heating will produce water and get dehydrated. Nitrates will give out nitrogen dioxide on the application of heat. This may vary in certain cases.

Complete answer: (i) In the case of carbonates, we can say that it will produce carbon dioxide gas when heated. One of the prominent exceptions for this is $N{a_{{\text{2}}}}C{O_3}{\text{ }}$ which doesn’t give any reaction to the application of heat. This is because the bond in sodium carbonate is strong and stable compared to other carbonates.
$CaC{O_3}$ will give us carbon dioxide on heating.
$CaC{O_{3}}\xrightarrow{{heat}}CaO + C{O_2}$
(ii) Hydrated salts become dehydrated on the application of heat. For the given examples the reaction will proceed as follows:
$CaC{l_2}.6{H_{2}}O\xrightarrow{{heat}}CaC{l_2} + 6{H_{2}}O$
$MgC{l_2}.6{H_2}O\xrightarrow{{heat}}MgO + 2HCl + 5{H_{2}}O$
(iii) Nitrates will give us different products depending on the compound when it is heated. Calcium nitrate will give us nitrogen dioxide and oxygen gas when heated.
$2Ca{(N{O_3})_{2}}\xrightarrow{{heat}}2CaO + 4N{O_{2}} + {O_2}$
Sodium nitrate on heating will decompose into sodium nitrite and liberate a colourless odourless oxygen gas.
$2NaN{O_3}\xrightarrow{{heat}}2NaN{O_2} + {O_{2}}$

Note:
Different inorganic salts will react differently towards heat and this is being manipulated in the qualitative analysis of salts or salt analysis. Carbonates can produce $C{O_{2}}$ which turns lime water milky. Most of the metal nitrates will decompose to give brownish colour $N{O_{2}}$ . Sulphates will give sulphur trioxides on heating and ammonium chloride will on heating sublimes.