F.4 Chem pls help !!!

Q1a. Why is an alkaline salt alkaline? why is acidic salt acidic?

Ans: An easier way to check whether a salt is acidic or alkaline is to look at the cation and anion of that salt.
If cation is stronger alkaline while anion is weak acidic, then it is an alkaline salt.
And vice versa for acidic salt.

e.g. K2CO3 => K+ is a strong cation (which form KOH, a strong alkaline in water),
while CO3(2-) is a weak anion (H2CO3 is a weak acid). So, it is an alkaline salt.



Q1b. when K2CO3 reacts with an acid it produces CO2 as well. Isn't that alkali reacts with acid to produce salt and water only?

Ans: An alkaline salt is a SALT. It is NOT an alkaline even though its pH is >7, which is alkaline (means alkalinity 鹼度是鹼性).

So, the equation: ALKALI + ACID → SALT + WATER
does not apply to alkaline SALT.
For example:
potassium hydroxide + nitric acid → potassium nitrate + water
KOH + HNO3 → KNO3 + H2O

If the alkaline salt is K2CO3, a carbonate, the applicable equation is:
CARBONATE SALT + ACID → SALT + WATER + CARBON DIOXIDE
where CARBON DIOXIDE is produced
For example:
Potassium carbonate + Nitric acid → Potassium nitrate + Water + Carbon dioxide
K2CO3 + 2HNO3 → 2KNO3 + H2O + CO2



Q.2. Redox equation for concentrated hydrochloric acid and potassium permanganate solution.

Ans: Mn in KMnO4 is 7+. In acidic solution of permanganate, Mn(7+) will reduce to Mn(2+) and water.

Half equation for the oxidizing agent (permanganate ion):
MnO4(-) + 8H(+) + 5e- → Mn(2+) + 4H2O ... (1)

Half equation for the reducing agent (Chloride ion):
2Cl(-) → Cl2 + 2e- ... (2)

Balancing the 2 ionic equations, (1) x2 and (2) x5 to eliminate electrons:
(1)x2: 2MnO4(-) + 16H(+) + 10e- → 2Mn(2+) + 8H2O
(2)x5: 10Cl(-) → 5Cl2 + 10e-
==> 2MnO4(-) + 16H(+) + 10Cl(-) → 2Mn(2+) + 8H2O + 5Cl2

To get the overall balanced equation, with 2K(+) + 6Cl(-) ions:
==> 2K(+) + 2MnO4(-) + 16H(+) + 10Cl(-) + 6Cl(-) → 2KCl + 2MnCl2 + 8H2O + 5Cl2
==> 2KMnO4(aq) + 16HCl(aq) → 2KCl(aq) + 2MnCl2(aq) + 8H2O(l) + 5Cl2(g)