1. compare the change in ph when equal volumes of STRONG ACID are added to a mix

Question

1. compare the change in ph when equal volumes of STRONG ACID are added to a mixture of a weak ACID and its conjugate base compared to when added to deionized water.

2. compare the change in ph when equal volumes of STRONG BASE are added to a mixture of a weak ACID and its conjugate base compared to when added to deionized water.

3. compare the change in ph when equal volumes of STRONG ACID are added to a mixture of a weak BASE and its conjugate base compared to when added to deionized water.

4. compare the change in ph when equal volumes of STRONG BASE are added to a mixture of a weak BASE and its conjugate base compared to when added to deionized water.

Explanation / Answer

1)
when strong acid is mixed with a weak acid and its conjugate base; the ionization of the strong acid is suppressed as compared to it's ionization in deionized water (in deionized water the dissociation of the strong acid is higher, so the concentration of H+ ions is higher and so lower is the pH).
so the pH of the mixture of (strong acid+weak acid and conjugate base) will be more than that of the pH of mixture of (strong acid + deionized water).

2)
when a strong base is added to a mixture of weak acid and it's conjugate base, the OH- ions neutralize the H+ ions from weak acid. Following it the concentration of OH- decreases implies pOH increases and hence pH decreases.
when strong base is added to deionized water, concentration of OH- ions is higher than previous case as there are no H+ ions to neutralize OH- ions. So, conc of OH- ions is high implies pOH is less implies pH is high.

so the pH of (strong base+deionized water) > pH of (strong base + weak acid and it's conjugate base)

3)
when strong acid is mixed with a weak base and its conjugate acid; the H+ ions of the strong acid neutralize the OH- from the weak base implies the conc of H+ ions decreases and thus pH increases.
in deionized water the conc of H+ ions of the strong acid is higher since there are no OH- ions to neutralize them, so the concentration of H+ ions is higher and the pH is low.
so the pH of the mixture of (strong acid+weak base and conjugate acid) will be more than that of the pH of mixture of (strong acid + deionized water).

4)
when strong base is mixed with a weak base and its conjugate acid; the ionization of the strong base is suppressed as compared to it's ionization in deionized water (in deionized water the dissociation of the strong base is higher, so the concentration of OH- ions is higher and so lower is the pOH and pH will be higher).
in a mixture of strong base and its conjugate acid, pOH is high such that pH is low;
in the case when a strong acid is added to deionized water conc of OH- is high such that pOH is low and pH is high.
so the pH of the mixture of (strong base+weak base and conjugate acid) will be less than that of the pH of mixture of (strong base + deionized water).

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