hkcee chemistry

1.
HCO3- is alkaline. The term 「alkaline」 means that the solution of HCO3- has a pH greater than 7.

HCO3- in water can give both H+(aq) and OH-(aq) in the following reactions:
HCO3-(aq) ≒ H+(aq) + CO32-(aq) …… (*)
HCO3-(aq) + H2O(l) ≒ H2CO3(aq) + OH-(aq) …… (**)
Reaction (**) has a greater tendency than reaction (*).

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2.
Soda lime (NaOH•CaO) can absorb both CO2­ or H2O.

In Biology experiments on photosynthesis, CaO used can absorb both CO2 and water vapour in the air. The plant gets CO2 from the air, but gets water from the soil. The absorption of water vapour by soda lime gives no effect on photosynthesis. Therefore, most Biology teachers would neglect the absorption of water vapour by soda lime.

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3.
This depends on whether an aqueous solution or solid iron(II) salt is used.

When the solution of an iron(II) salt is used, the solvent (water) in the solution would dilute the concentrated HNO3. Actually, the reaction is between iron(II) ions and moderately concentrated HNO3. Therefore, NO gas is formed.
3Fe2+ + 4H+ + NO3- → 3Fe3+ + 2H2O + NO

When the solid of an iron(II) salt is used, the concentrated HNO3 would not be diluted. The reaction between iron(II) ions and concentrated HNO3 gives NO2 gas.
Fe2+ + 2H+ + NO3- → Fe3+ + H2O + NO2