1. (a) Carbon Dioxide ($CO_2$). (b)
$CaCO_3(s) + 2HCl(aq) \rightarrow CaCl_2(aq) + H_2O(l) + CO_2(g)$
(c) X is a Metal Carbonate (like Limestone), which is Basic in nature.
2. (a) Calcium Oxychloride ($CaOCl_2$). (b) It contains Chlorine ($Cl_2$),
which is loosely held and escapes as a gas. (c) It reacts with $CO_2$ in air:
$CaOCl_2 + CO_2 \rightarrow CaCO_3 + Cl_2$
3. (a) NaCl: Neutral (Strong Acid + Strong Base). (b) $NH_4Cl$: Acidic
(Strong Acid + Weak Base). (c) $Na_2CO_3$: Basic (Weak Acid + Strong Base).
4. In Test Tube A (HCl). HCl is a strong acid and dissociates completely,
providing more $H^+$ ions. Acetic acid is weak and dissociates partially.
5. (a) X is Hydrogen ($H_2$), Y is Carbon Dioxide ($CO_2$). (b) Hydrogen
reduces hot CuO to Copper:
$CuO(s) + H_2(g) \xrightarrow{\Delta} Cu(s) + H_2O(l)$
6. Approximately pH 1-2 (or around 1.5).
7. Milk of Magnesia ($Mg(OH)_2$) or Baking Soda
($NaHCO_3$).
8. Antacid neutralises the excess acid. The reaction is
called Neutralisation.
9. No. NaOH is a strong base and is highly corrosive. It
will damage the stomach lining. Only mild bases (weak alkalis) can be used as antacids.
10. $Ca_3(PO_4)_2$ (Calcium Phosphate) or
$Ca_{10}(PO_4)_6(OH)_2$ (Hydroxyapatite).
11. Bacteria in the mouth break down sugars from food to
produce acids (like lactic acid).
12. Toothpastes are generally basic (pH > 7). They
neutralise the acid formed in the mouth after eating, preventing enamel corrosion.
13. Yes, it is suitable. A pH of 8.0 means it is mildly
basic, which helps neutralise the acid in the mouth.
14. (a) Blue crystals turn white (due to loss of water of crystallisation).
(b) It is a Chemical change (composition changes). (c) On adding water, the white powder turns blue again,
showing the formation of $CuSO_4 \cdot 5H_2O$.
15. Both A and R are True, and R is the correct explanation of A.
16. The water molecules are chemically bonded within the crystal lattice.
They are not like surface moisture (adsorbed water) and are part of the crystal structure.
17. Strong Acids: Hydrochloric acid (HCl), Nitric acid ($HNO_3$), Sulphuric
acid ($H_2SO_4$). Weak Acids: Citric acid, Acetic acid ($CH_3COOH$), Formic acid (HCOOH).
18. Turmeric (in curry) is a natural indicator. In contact with soap (which
is basic), its yellow colour turns reddish-brown. On washing with water (neutral), the colour reverts to
yellow.
19. The concentration of $OH^-$ ions increases, as more NaOH dissolves and
releases more hydroxide ions.
20. (Solvay Process)
$NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3$
$2NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2$
