Answer: 1. B. 1.3
2. D. self-ionization
3. A. acidic
4. HCl is a weak acid; \(CH_3COOH\) is a weak acid.
5. A. \(K_b=\frac{[OH^-][C_5H_5NH^+]}{[C_5H_5N]}\)
Explanation:
1. pH is the negative logarithm of hydrogen ion concentration.
\(pH=-log[H^+]\)
Given: \([H^+]=5.0\times 10^{-2}=0.05\)
\(pH=-log[0.05M]=1.30\)
2. An acid is a substance which donates \(H^+\) ions when dissolved in water.
A base is a substance which donates \(OH^-\) ions when dissolved in water.
Thus as water ionizes to give both ions, it acts as both acid and base.
\(H_2O\rightarrow H^++OH^-\) which is called as self ionization.
3. pH is the measure of acidity or alkalinity of a solution. \Acids have pH less than 7, neutral solutions have pH of 7 and basic solutions have pH more than 7.
As the given solution has a pH of 6.8 which is less than 7, it is an acidic solution.
4. Strong acids are those acids which undergo complete dissociation when dissolved in water.
\(HCl\rightarrow H^++Cl^-\)
Weak acids are those acids which do not undergo complete dissociation when dissolved in water.
\(CH_3COOH\rightleftharpoons CH_3COO^-+H^+\)
5. Dissociation constant is the ratio of product of concentration of products to the product of concentration of reactants each raised to their stochiometric coefficients.
\(C_5H_5N+H_2O\rightarrow C_5H_5NH^++OH^-\)
\(K_b=\frac{[OH^-][C_5H_5NH^+]}{[C_5H_5N]}\)
The concentration of water is ignored as it is in large excess and thus does not effect the dissociation of pyridine.
