1. X (brown gas on heating green salt) = Ferrous Sulphate
($FeSO_4 \cdot 7H_2O$).
Y (brown gas) = Nitrogen Dioxide ($NO_2$).
Z
(residue) = Ferric Oxide ($Fe_2O_3$).
$2FeSO_4(s) \xrightarrow{\Delta} Fe_2O_3(s) + SO_2(g) + SO_3(g)$
2. M (kept under kerosene) = Sodium (Na) or Potassium (K).
Reason: They are highly reactive and catch fire on exposure to air.
$4Na + O_2 \rightarrow 2Na_2O$ (vigorous)
3. A (reddish brown metal, black on heating in air) = Copper
(Cu).
B (Black compound) = Copper Oxide (CuO).
$2Cu(s) + O_2(g) \xrightarrow{\Delta} 2CuO(s)$
On passing $H_2$: $CuO + H_2 \rightarrow Cu + H_2O$.
4. M (burns with dazzling white flame) = Magnesium (Mg).
N (white ash) = Magnesium Oxide (MgO). MgO is basic and turns red litmus blue (dissolves in
water to form Mg(OH)$_2$).
5. Metal X (displaces Cu from CuSO$_4$, turns blue to green)
= Iron (Fe).
$Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$
6. Aluminium is highly reactive but does not corrode easily because it forms
a thin, protective layer of Aluminium Oxide ($Al_2O_3$) on its surface which prevents further reaction.
7. Copper and Silver do not react with dilute acids because they are below
Hydrogen in the reactivity series. They cannot displace $H^+$ ions from acids.
8. Gold and Silver are used for jewellery because they are lustrous,
malleable, ductile, non-reactive and do not corrode.
9. Calcium floats on water because the Hydrogen gas evolved sticks to its
surface as bubbles, making it lighter.
$Ca(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq) + H_2(g)$
10. Zinc oxide is Amphoteric. It reacts with both acids and bases:
$ZnO + 2HCl \rightarrow ZnCl_2 + H_2O$
$ZnO + 2NaOH \rightarrow Na_2ZnO_2 + H_2O$
11. Alloys are homogeneous mixtures of two or more metals (or a metal and a
non-metal). They are harder and have lower melting points than pure metals. They resist corrosion better.
12. Galvanisation is coating iron with a thin layer of Zinc. Even if
scratched, Zinc is oxidised first (being more reactive), protecting Iron underneath. This is called
sacrificial protection.
