State giving reasons if:
(a) Zinc metal and aluminium metal can be distinguished by heating the metal powders separately in two different test tubes with concentrated sodium hydroxide solution.
(b) Zinc nitrate and lead nitrate can be distinguished by adding ammonium hydroxide solution to the salt solution.
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(a) No, zinc and aluminium cannot be distinguished by this method. Both metals react with concentrated sodium hydroxide solution to form soluble sodium salts and liberate hydrogen gas, which burns with a pop sound.
Zn + 2NaOH ⟶ Na2ZnO2 + H2
2Al + 2NaOH + 2H2O ⟶ 2NaAlO2 + 3H2
(b) Yes, they can be distinguished. With zinc nitrate, ammonium hydroxide gives a white precipitate of Zn(OH)2 which is soluble in excess of ammonium hydroxide. With lead nitrate, a white precipitate of Pb(OH)2 is formed which is insoluble in excess of ammonium hydroxide.