Question

Which of the following statements about acid-base titrations are true?

(i) If 0.200MNaOH is used to titrate 50.0mL of 0.100M hydrochloric acid, it will take 25.0mL of NaOH to reach the equivalence point.

(ii) If 0.100MNaOH is used to titrate 50.0mL of 0.100M sulfuric acid (instead of 50.0mL of 0.100M hydrochloric acid), the pH at the equivalence point will be <7.00 because sulfuric acid is diprotic.

(iii) The pH=7.00 at the equivalence point for a strong acid – strong base titration.

statements (i) and (ii) are true.

statements (i) and (iii) are true.

statements (ii) and (iii) are true.

all three statements are true.

only one statement is true.

Answer 1

all three statements are true.

(i) If 0.200MNaOH is used to titrate 50.0mL of 0.100M hydrochloric acid, it will take 25.0mL of NaOH to reach the equivalence point.

HCl + NaOH ----> NaCl + H2O

1mole HCl = 1mole NaOH. Therefore, 0.2M*25mL = 0.1M*50mL

(ii) If 0.100MNaOH is used to titrate 50.0mL of 0.100M sulfuric acid (instead of 50.0mL of 0.100M hydrochloric acid), the pH at the equivalence point will be <7.00 because sulfuric acid is diprotic.

H2SO4 + 2NaOH ------>2Na2SO4 + 2H2O

1mole H2SO4 = 2moles NaOH. Therefore, 0.1M*50mL = 0.1*100mL but only 25mL is added. Hence amount of H2SO4 is more so pH<7

(iii) The pH=7.00 at the equivalence point for a strong acid – strong base titration.