Discuss the factors affecting acid strength by examples.
At experimentally, the strength of acid base decided by the value of $\mathrm{pH}$.
Theoretically the extent of dissociation of an acid depends on the strength and polarity of the $\mathrm{H}$ - $A$ bond. i.e. $\left[\mathrm{H}^{+}\right]$and strength will be decide.
$(i)$ When strength of $\mathrm{H}-\mathrm{A}$ bond decreases, that is, the energy required to break bond decreases, $HA$ becomes a stronger acid.
$(ii)$ When the $\mathrm{H}-\mathrm{A}$ bond becomes more polar, i.e. the electronegativity difference between the atoms $\mathrm{H}$ and A increases and there is marked charge separation, clavate of the bond becomes easier there by increasing the acidic. Thus, polarity of bond $\alpha$ difference of electronegativity $\alpha$ Acidity.
$(iii)$ The strength of $\mathrm{H}-\mathrm{A}$ in only one period : In the row of the periodic table, $\mathrm{H}-\mathrm{A}$ bond polarity becomes the deciding factor for determining the acid strength. As the electronegativity of a increases, the strength of acid also increases. For example, $\rightarrow$ Electronegativity A increases $\rightarrow \mathrm{CH}_{4}<\mathrm{NH}_{3}<\mathrm{H}_{2} \mathrm{O}<\mathrm{HF} \rightarrow$ Acid strength increases $\rightarrow$ The acidic strength in group : In the group of the periodic table, $H$ - $A$ bond strength is a more important factor in determining acidity than its polar nature. As the size of $\mathrm{A}$ increases down the group. $\mathrm{H}-\mathrm{A}$ bond strength decreases and so the acid strength increases. For example,
$\rightarrow$ Size increases of $\mathrm{A} \rightarrow \mathrm{HF} \ll \mathrm{HCl} \ll \mathrm{HBr} \ll \mathrm{HI} \rightarrow$ Acid strength increases $\rightarrow$
Calculate the $pH$ of the solution in which $0.2 \,M\, NH _{4} Cl$ and $0.1 \,M\, NH _{3}$ are present. The $pK _{ b }$ of ammonia solution is $4.75$
$50\ ml$ of $0.02\ M$ $NaHSO_4$ is mixed with $50$ $ml$ of $0.02\ M\ Na_2SO_4$. Calculate $pH$ of the resulting solution.$[pKa_2 (H_2SO_4) = 2]$
Values of dissociation constant, $K_a$ are given as follows
Acid | $K_a$ |
$HCN$ | $6.2\times 10^{-10}$ |
$HF$ | $7.2\times 10^{-4}$ |
$HNO_2$ | $4.0\times 10^{-4}$ |
Correct order of increasing base strength of the base $CN^-,F^-$ and $NO_2^-$ will be
A weak acid $HA$ has a $K_a$ of $1.00 \times 10^{-5} $. If $0.100\,mol$ of this acid is dissolved in one litre of water the percentage of acid dissociated at equilibrium is closest to.....$\%$
$5\%$ ionization is occur in $0.01$ $M$ $C{H_3}COOH$ solution. Calculate its dissociation constant.