Acids bases and salts – Question bank
CLASSIFICATION OF ACIDS AND BASES
Based on Strength
Strong acid: HCl → H+ + Cl– is completely ionized (100%)
Examples : HCl, H2SO4, HNO3, HBr, HI, HClO4
Weak acid: CH3COOH ↔ CH3COO– + H+ is only partially ionized (1-2%)
Examples : HI, HCOOH, CH3COOH, H2CO3, H3PO4, (COOH)2
Strong Base: NaOH → Na+ + OH– is completely ionized (100%)
Examples: NaOH, KOH, LiOH, Ca(OH)2, Ba(OH)2, Mg(OH)2
Weak Base: NH4OH ↔ NH4+ + OH– is only partially ionized (1-2%)
Examples: NH4OH, N(CH3)3, C5H5N, Fe(OH)3, Al(OH)3
Based on basicity of the acid
Monobasic acid: One replaceable hydrogen is released on ionization
Examples : HCl, HNO3, HBr, HI, HClO4
Dibasic acid: Two replaceable hydrogens are released in 2 steps
Examples : H2SO4, H2SO3, H2CO3, (COOH)2
Based on acidity of the base
Monoacidic base: One replaceable hydroxyl ion is released on ionization
Examples : NaOH, KOH, LiOH, CsOH
Diacidic base: Two replaceable hydroxyl ions are released in 2 steps
Examples :Ca(OH)2, Ba(OH)2, Mg(OH)2, Fe(OH)2
CHARACTERISTIC REACTIONS OF ACIDS
a) Reaction with active metals ( Mg, Al, Zn, Fe, Sn)
Active metals dissolve in acids forming respective salt and release of hydrogen gas
2HCl + Zn → ZnCl2 + H2
2HCl + Fe → FeCl2 + H2
2HNO3 + Mg → Mg(NO3)2 + H2
6HCl + 2Al →2AlCl3 + 3H2
b) Reaction with metal oxides
Acids react with basic metal oxides
2HCl + ZnO → ZnCl2 + H2O
2HNO3 + CuO → Cu(NO3)2 + H2O
2HNO3 + PbO → Pb(NO3)2 + H2O
H2SO4 + Na2O → Na2SO4 + H2O
c) Reaction with metal carbonates/bicarbonate
Acids react with metal carbonates/bicarbonates to form salt and release carbon dioxide gas
2HCl + ZnCO3 → ZnCl2 +H2O + CO2
H2SO4 + Na2CO3 → Na2SO4 +H2O + CO2
HCOOH + NaHCO3 → HCOONa +H2O + CO2
2HNO3 + CaCO3 → Ca(NO3)2 +H2O + CO2
CHARACTERISTIC REACTIONS OF BASES
a) Reaction with non metal oxides
Ca(OH)2 + CO2 → CaCO3 + H2O
c) Reaction with ammonium salts
NaOH + NH4Cl → NaCl + H2O + NH3
Ca(OH)2 + NH4Cl → CaCl2 + H2O + NH3
2KOH + (NH4)2SO4 → K2SO4 + 2H2O + 2NH3
NaOH + NH4NO3 → NaNO3 + H2O + NH3
pH SCALE
pH = – log10 [H+]
Acidity or alkalinity can easily be measured using the pH scale. The scale ranges from 0 (most acidic) to 14 (most alkaline).
The pH of a solution can be easily found out using indicators that change color with pH of solution to which they are added.
| Acid | Neutral | Basic | |
| Litmus | Red | No change | Blue |
| Universal | Red | Green | Purple |
| Methyl Orange | Red | orange | Yellow |
| Phenolphthalein | colorless | colorless | Pink |
SALTS
They are ionic compounds that are electrically neutral. Salts are formed during neutralization reaction between acid and base. They are also formed in reaction of acid with active metal and neutralization reactions of acids with metal oxides, metal carbonate and metal hydroxide.
NEUTRALIZATION REACTION
Acid and base reacts to form salt and water with liberation of heat
HCl + NaOH → NaCl + H2O
HCl + KOH → KCl + H2O
H2SO4 + 2KOH → K2SO4 + 2H2O
2HCl + Zn(OH)2 → ZnCl2 + 2H2O
2HNO3 + Ba(OH)2 → Ba(NO3)2 + 2H2O
3HNO3 + Fe(OH)3 → Fe(NO3)3 + 3H2O
H2CO3 + 2KOH → K2CO3 + 2H2O
HNO3 + NaOH → NaNO3 + H2O
HBr + KOH → KBr +H2O
HCl + NH4OH → NH4Cl +H2O
2H3PO4 + 3Ca(OH)2 → Ca3(PO4)2 + 6H2O
H2SO4 + 2NH4OH → (NH4)2SO4 + 2H2O
2HCl + Mg(OH)2 → MgCl2 + 2H2O
H3PO4 + 3NaOH → Na3PO4 + 3H2O
H2SO4 + Mg(OH)2 → MgSO4 + 2H2O
H3PO4 + 3NH4OH → (NH4)3PO4 + 3H2O