What is the pH after 0.028 moles of NaOH is added to a 100.0mL buffer solution c
ID: 500482 • Letter: W
Question
What is the pH after 0.028 moles of NaOH is added to a 100.0mL buffer solution containing 0.45M HOBr and 0.55M NaOBr ? Ka HOBr = 2.5 x 10-9
QUESTION 2
Which of the following occurs when NaOH is added to a buffer containing (CH3)3N and (CH3)3NH+?
Select all that apply.
The concentraion of
The pH will decrease.
The concentraion of
(CH
The pH will increase.
The concentraion of
1 points
QUESTION 3
When NaOH is added to a HF / NaF buffer, what happens to the following values?
Concentration of HF
Concentration of F-?
pH
Decreases
Increases
1 points
QUESTION 4
Of the following, which is the best base to create a buffer with a pH = 8.0?
Aniline, Kb = 4.3 x 10-10
Pyridine, Kb = 1.7 x 10-9
Ethylamine, K
Hydrazine, K
The concentraion of
The pH will decrease.
The concentraion of
(CH
The pH will increase.
The concentraion of
Explanation / Answer
1) What is the pH after 0.028 moles of NaOH is added to a 100.0mL buffer solution containing 0.45M HOBr and 0.55M NaOBr ? KaHOBr = 2.5 x 10-9
When NaOH is added to the buffer it will react with HOBr to give NaOBr
The moles of HOBr initially present = Molarity X volume (L) = 0.45 X 0.1 = 0.045 moles
Moles of NaOBr initialy present = Molarity X volume (L) = 0.55 X 0.1 = 0.055 moles
On adding 0.028 moles of NaOH
Moles of HOBr left = 0.045 - 0.028 = 0.017 moles
Moles of NaOBr present after addition = 0.055 + 0.028 = 0.083 moles
the pH of buffer will be
pH = pKa + log [salt] / [acid]
pKa = -logKa = -log(2.5 x 10-9) = 8.602
pH = 8.602 + log [NaOBr] / [HOBr] = 8.602 + log [0.083/0.017] = 9.291
2) Which of the following occurs when NaOH is added to a buffer containing (CH3)3N and (CH3)3NH+?
On addition of NaOH,
The concentration of (CH3)3NH+ will decrease
The concentration of (CH3)3N will increase
The pH will increase
3) When NaOH is added to a HF / NaF buffer, what happens to the following values
The Concentration of F- will increase
The concentration of HF will decrease
The pH will increase
4) Of the following, which is the best base to create a buffer with a pH = 8.0
The best buffer will be from pKa near to the desired pH
Kb of ethylamine is s 4.3 x 10-4 (so the Ka = 2.3 X 10-11)
Kb of hydrzine is 1.3*10^-6 (so ka = 7.69 X 10-9) pKa = 8.11
so this will be best
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