Question 11 Not yet answered Marked out of 1.00 P Flag question Indicators Pheno

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Question 11 Not yet answered Marked out of 1.00 P Flag question Indicators Phenolphthalein is a commonly used indicator that is colorless in the acidic form (pH 10.0). It is a weak acid with a pKa of 8.7. What is the ratio of the conjugate base concentration to the acid concentration, that is, [B HB] when the indicator switches to the acidic color? Hint given in feedback. Answer Question 12 Not yet answered Marked out of 1.00 Use the result to the above question to determine what percent is in the acidic form when the acid color is first apparent? Answer Flag question Question 13 Not yet answered What is B YHB] when the indicator switches to the basic color? Marked out of 1.00 Answer P Flag question Question 14 Not yet answered Use the result to the above question to determine what percent is in the basic form when the base color is first apparent? Not graded Answer Flag question

Explanation / Answer

Q1

if pH = 8.3

then

p H= pKa + log(B-/HB)

8.30 = 8.70 + log(B-/HB)

10^(8.3-8.7) = (B-/HB)

(B-/HB) = 0.398

Q2.

assume HB =1, so

B- = 0.398*1 = 0.398

% of HB = HB/Total * 100%

% of HB = 1/(1+0.398) * 100% = 71.5%

Q3

pH pink = 10

if

pKa = 8.7

then

pH = pKa + log(B-/HB)

10= 8.3 + log(B-/HB)

(B-/HB) = 10^(10-8.3) = 50.11

Q4

find % of acidic form

assume HB = 1, so B- = 1/50.11 = 0.0199

% acidic = (1)/(1+0.0199 ) * 100

% acidic = 98.048%

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