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What would you observe in the following cases?
(i) Sodium and potassium are placed in cold water.
(ii) Burning magnesium is introduced into steam.
(iii) Copper hydroxide is heated.
(iv) Potassium nitrate is heated strongly.
(v) Copper nitrate is heated strongly.
(vi) Mercuric nitrate is heated strongly.

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Solution

(a) A violent reaction occurs when sodium and potassium are placed in cold water. They form the respective alkalis and liberate hydrogen gas.

2Na + 2H2O 2NaOH + H2Sodium Water Sodium Hydrogen gas hydroxide 2K + 2H2O 2KOH + H2 Potassium Water Potassium Hydrogen gas hydroxide

(b) Burning magnesium reacts with steam to form magnesium oxide and liberates hydrogen gas.

2Mg + H2O 2MgO + H2 Magnesium Steam Magnesium oxide Hydrogen gas

(c) On heating, copper hydroxide decomposes to form cupric oxide and water.

Cu(OH)2 decomposesheated CuO + H2OCopper hydroxide Cupric oxide Water

(d) On heating, potassium nitrate decomposes to form potassium nitrite and oxygen.

2KNO3 decomposeheat 2KNO2 + O2Potassium nitrate Potassium nitrite Oxygen gas

(e)When copper nitrate is heated strongly, it decomposes to form cupric oxide and liberates nitrogen dioxide and oxygen.

2Cu(NO3)2 (s) decomposeheat 2CuO(s) + 4NO2(g) + O2(g)Copper nitrate Cupric oxide Nitrogen dioxide Oxygen gas

(f) On heating, mercuric nitrate decomposes to form a metal, nitrogen dioxide and oxygen.

Hg(NO3)2 (s) decomposeheat Hg(l) + 2NO2(g) + O2(g)Mercuric nitrate Mercury Nitrogen dioxide Oxygen gas

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