1. what is: A. the conjugate base of carbonic acid, H2CO3? B. Conjugate acid of
ID: 304344 • Letter: 1
Question
1. what is: A. the conjugate base of carbonic acid, H2CO3? B. Conjugate acid of the HSO4- ion? And how do you know this. Explain.
2. You add 0.235 g of KOH to 200.0 mL of water at 25 degrees celcius. What is [H30+] in this solution? (the answer is 4.77*10^-13 I just dont know how to solve it).
3. An acid-base equilibrium system is created by dissolving 0.20mol CH3COOH in water and diluting the resulting solution to a volume of 1.0 L. What is the effect of adding 0.020 mol CH3COO-(aq) to this solution? How will pH change? (calculate the pH before and after the addition Ka of CH3COOH is 1.76*10^-5)? How will conentrations of CH3COOH and CH3COO- at equilibrium change?
Explanation / Answer
1) H2CO3 ----> HCO3-(conjugate base) + H+
HSO4- ----> SO4^-2(conjugate base) + H+
2) Molarity of KOH solution(M) = (w/M)*(1000/V)
= (0.235/56.1)*(1000/200)
= 0.0209 M
so that, [OH-] = 0.0209 M
[H3O+] = kW/[OH-]
= (1.0*10^-14)/(0.0209)
= 4.77*10^-13 M
3) concentration of CH3COOH = 0.2/1 = 0.2 M
pH before
pH = 1/2(pka-logC)
= 1/2(4.75-log0.2)
= 2.72
concentration of ch3coo- = 0.02/1 = 0.02 M
pH after addition
pH = pka + log(CH3COO-/CH3COOH)
pka of CH3COOH = -logKa
= -log(1.76*10^-5)
= 4.75
pH = 4.75+log(0.02/0.2)
= 3.75
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