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Equilibrium

Question
CBSEENCH11008424

A Weak acid, HA has a Ka of 1.00 x 10-5. If 0.100 mole of this percentage of acid dissociated at equilibrium is closest to:

  • 99.0%

  • 1.00%

  • 99.9 %

  • 0.100%

Solution

B.

1.00%

HA space leftwards harpoon over rightwards harpoon space straight H to the power of plus space plus space straight A to the power of minus
straight K subscript straight a space space equals space fraction numerator left square bracket straight H to the power of plus right square bracket left square bracket straight A to the power of minus right square bracket over denominator left square bracket HA right square bracket end fraction space equals space fraction numerator left square bracket straight H to the power of plus right square bracket over denominator left square bracket HA right square bracket end fraction
left square bracket straight H to the power of plus right square bracket space equals space square root of straight K subscript straight a left square bracket HA right square bracket end root space equals space square root of 1 space straight x space 10 to the power of negative 5 end exponent space 0.1 end root
space equals square root of 1 space straight x 10 to the power of negative 6 end exponent end root space equals space 1 space straight x space 10 to the power of negative 3 end exponent

straight alpha space equals space fraction numerator actual space ionization over denominator molar space concentration end fraction space equals space fraction numerator 10 to the power of negative 3 end exponent over denominator 0.1 end fraction space equals space 10 to the power of negative 2 end exponent
percent sign space of space acid space dissociated space space equals space 10 to the power of negative 2 end exponent space straight x space 100
space equals space 1 percent sign