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An acid -base indicator has a Ka of 3.0 ...

An acid -base indicator has a `Ka of 3.0 xx 10^(-5) ` The acid form of the indicator is red and the basic form is blue. Then

A

pH is 4.05 when indicator is 75 % red

B

pH is 5.00 when indicator is 75% blue

C

pH is 5.00 when indicator is 75 % red

D

pH is 4.05 when indicator is 75% blue

Text Solution

Verified by Experts

The correct Answer is:
A, B
` K_a =([H^(+) ][In^(-)])/( [HIn]) `
` if 75% red rArr ([HI_n])/([In^(-)]) =(75)/(25) =3 `
` rArr [H^(+) ] =3 xx 10 ^(-5) xx 3 `
` pH =5- log 9 =4.05`
` if 75% blue rArr ([In^(-)])/([HI_n]) = 3 `
` [H^(+) ] = 10 ^(-5) rArr pH =5`
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Knowledge Check

  • An acidic indicator ionises as I_n H hArr In^(-) + H^(+) . The molecular and ions of the indicator show different colours. The indicator changed it colour if its acidic of basic form completely predominate. What is the percentage of basic form acidic indicator . (P^(ka) =6) is an aqeous NaCl soluition at 25% C

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    B
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    C
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