A 0.20-molar solution of a weak monoprotic acid, HA, has a pH of 3 00. The ioniz

Question

A 0.20-molar solution of a weak monoprotic acid, HA, has a pH of 3 00. The ionization constant of this acid is A) 5.0 times 10^-7 B) 2.0 times 10^7 C) 5.0 times 10^-6 D) 5.0 times 10^-3 E) 24 times 10^-3 As the number of oxygen atoms increases in a series of oxygen acids, such as HXO_3 HXO_2, HXO_3, ... which of the following is generally true? A) The acid strength varies unpredictably. B) The acid strength decreases only if X is a nonmetal. C) The acid strength decreases only if X is a metal. D) The acid strength decreases whether X is a nonmetal or a metal. E) The acid strength increases. Which of the following does NOT behave as an electrolyte when it is dissolved in water? A) CH_3OH B) K_2CO_3 C) NH_4Br D) HI E) Sodium acetate_3CH_3COONa When phenolphthalein is used as the indicator in a titration of an HCI solution with a solution of NaOH, the indicator undergoes a color change from clear to red at the end point. This color change occurs abruptly because A) Phenolphthalein is a very strong acid that is capable of rapid dissociation B) The solution being titrated undergoes a large pH change near the end point of the titration C) Phenolphthalein undergoes an irreversible reaction in basic solution D) OH^- acts as a catalyst for the decomposition of phenolphthalein E) Phenolphthalein is in the rate-determining step of the reaction between H_3O^+ and OH^- H_2PO_4- + HBO_3^2- HPO_4^2- + H_2BO_3^- The equilibrium constant for the reaction represented above is greater than 1. Which of the following gives the correct relative strengths of the acids and bases? A)H_2PO_4^- > H_2BO_3^- B) H_2BO_3^- > H_2PO_4^- > H_2PO_4 D) H_2BO_3^- > H_2PO_4^- E) H_2PO_4^- = H_2BO_^- HBO_3^2- >HPO_4^2- HBO_3^2- >HPO_4^2- HPO_4^2- > HBO_3^2- HPO_4^2- > HBO_3^2- HPO_4^2- = HBO_3^2- All of the following species can function as Bronsted - Lowry bases in solution EXCEPT A) H_2O B) NH_3 C) S^2- D) NH_4^+ E) HCO_3^- In the titration of a weak acid of unknown concentration with a standard solution of a strong base, a pH meter was used to follow the progress of the titration. Which of the following is true for this experiment? A) The pH is 7 at the equivalence point B) The pH at the equivalence point depends on the indicator used. C) The graph of pH versus volume of base added rises gradually at first and then much more rapidly. D) The graph of pH versus volume of base added shows no sharp rise. E) The [H^+] at the equivalence point equals the ionization constant of the acid. A) a solution with a pH less than 7 that is not a buffer solution B) a buffer solution with a pH between 4 and 7 C) a buffer with a pH between 7 and 10 D) a solution with a pH greater than 7 that is not a buffer solution E) a solution with a pH of 7 Ionization constants: CH_3COOH K = 1.8 times 10^-5 NH_3 K = 1.8 times 10^-5 H_2CO_3: K_2 = 4 times 10^-7; K_21 = 4 times 10^-11 A solution prepared to be initially 1 M in NaCl and 1 M in HCI. A solution prepared to be initially 1 M in Na_2CO3 and 1 M in CH_3COONa A solution prepared to be initially 0.5 M in CH_3COOH and 1 M in CH_3COONa If the acid dissociation constant, K_a, for an acid HA is 8 times 10^-4 25 degree C, what percent of the acid is dissociated in a 0.50 M solution of HA at 25 degree C? A) 0.08% B) 0.2% C)1% D) 2% E)4%

Explanation / Answer

Solution-
The equation is HA <==> H+ + A-,

And hence Ka = [H+][A-]/[HA].

[A-] = [H+] (from the balanced equation),

[HA] = 0.2 - [H+] = 0.199M approx=0.2

Ka = (1x10^-3)^2/0.2 = 5 x 10^-6.

Hence option C is correct

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