Which one of these net ionic equations represents the reaction of a strong base

Question

Which one of these net ionic equations represents the reaction of a strong base with a weak acid? A) H^+(aq) + OH^-(aq) rightarrow H_2O(aq) B) H^+(aq) + CH_3NH_2(aq) rightarrow CH_3NH_3^+(aq) C) OH^-(aq) + HCN(aq) rightarrow H_2O(aq) + CN^-(aq) D) HCN(aq) + CH_3NH_2(aq) rightarrow CH_3NH_3^+(aq) + CN^-(aq) What is the pH of an aqueous solution that contains 3.7 tunes 10^20 H_2O^+ ions per liter of solution? A) 2.70 B) 3.35 C) 3.21 D) 10.65 E) 11.30 The pH of a certain solution is 3.0. HOw many H^+(aq) ions are there in 1.0 L of the solution? A) 0.01 ions B) 100 ions C) 2 ions D) 6.0 times 10^21 ions E) 6.0 times 10^20 ions Assuming equal concentrations of conjugate base and acid, which one of the mixtures is suitable for making a buffer solution with an optimum pH of 3.3-3.4 A) CH_3COONa/CH_3COOH (K_a = 1.8 times 10^-5) B) NH_3/NH_4CI (K_a = 5.6 times 10^-10) C) NaOCI/HOCI (K_a = 3.2 times 10^-8) D) NaNO_2/HNO_2 (K_a = 4.5 times 10^-4) The OH^- concentration in a 3.75 times 10^-3 M Ca(OH)_2 solution is A) 7.5 times 10^-3 M. B) 1.5 times 10^-2 M. C) 1.3 times 10^-12 M. D) 1.0 times 10^-7 M. E) 1.0 times 10^-14 M.

Explanation / Answer

1)

A is net ionic reaction of strong acid and strong base

B is for Strong acid and weak base

C is strong base and weak acid

D is for weak acid and weak base

Answer: C

2)

number of ion = 3.7*10^20

number of mol = number of ion / Avogadro’s number

= (3.7*10^20) / (6.022*10^23)

= 6.144*10^-4

volume is 1 L

So,

[H3O+] = number of mol / volume

= (6.144*10^-4 mol)/1L

= 6.144*10^-4 M

pH = -log [H3O+]

= -log (6.144*10^-4)

= 3.21

Answer: C

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