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The p-Block Elements

Multiple Choice Questions

501.

Aqueous solution of ferric chloride is acidic due to

ionization
polarization
dissociation
hydrolysis

502.

The correct order of heat of formation of halogen acids is

HI > HBr > HCl > HF
HF > HCl > HBr > HI
HCl > HF > HBr > HI
HCl > HBr > HF > HI

503.

The hydroxide insoluble in NH₄OH + NH₄Cl is

Al(OH)₃
Ca(OH)₃
Zn(OH)₂
Mg(OH)₂

504.

Precipitate of AgCl is soluble in liquid NH₃ the compound forms

Ag(NH₄)₂OH
Ag(NH₄)₂Cl
Ag(NH₃)₂OH
Ag(NH₃)₂Cl

505.
In qualitative analysis, in III group NH₄Cl is added before NH₄OH because

to increase the concentration of NH $_{4}^{+}$ ions

to increase the concentration of Cl^- ions

to reduce the concentration of OH^- ions

to increase the concentration of OH^- ions

to reduce the concentration of OH^- ions

In the presence of strong electrolyte, degree of dissociation of weake electroylte ( having common on) gets suppressed due to common ion effect.

${NH}_{4} Cl being a strong electrolyte, dissociates as {NH}_{4} Cl \to {NH}_{4}^{+} + {Cl}^{-} and {NH}_{4} OH as {NH}_{4} OH ⇌ {NH}_{4}^{+} + {OH}^{-}$

Due to the presence of common ion, the degree of dissociation of NH₄OH decrease. Thus, less
OH^- ions are produced which are sufficient only for the precipitation of hydroxides of III group
radicals and not ofhigher group radicals.