Respuesta :
The question is incomplete, here is the complete question:
A student prepares a 0.21 mM aqueous solution of trimethylacetic acid. Calculate the fraction of trimethylacetic acid that is in the dissociated form in his solution. Express your answer as a percentage. You will probably find some useful data in the ALEKS Data resource. Round your answer to 3 significant digits.
Answer: The percent of dissociation of trimethylacetic acid is 19.5 %
Explanation:
We are given:
Concentration of trimethylacetic acid = 0.21 mM = 0.00021 M (Conversion factor: 1 mole = 1000 millimoles )
The chemical equation for the dissociation of trimethylacetic acid follows:
[tex]C_4H_9COOH\rightleftharpoons C_4H_9COO^-+H^+[/tex]
Initial: 0.00021
At eqllm: 0.00021-x x x
The expression of [tex]K_a[/tex] for above equation follows:
[tex]K_a=\frac{[C_4H_9COO^-][H^+]}{[C_4H_9COOH]}[/tex]
We know that:
[tex]K_a\text{ for }C_4H_9COOH=1\times 10^{-5}[/tex]
Putting values in above expression, we get:
[tex]1\times 10^{-5}=\frac{x\times x}{(0.00021-x))}\\\\x=0.000041,-0.000051[/tex]
Neglecting the negative value of 'x' because concentration cannot be negative.
To calculate the fraction of dissociation, we use the equation:
[tex]\text{Percent of dissociation}=\frac{[H^+]}{[C_4H_9COOH]}\times 100[/tex]
Putting values in above equation, we get:
[tex]\text{Percent of dissociation}=\frac{0.000041}{0.00021}\times 100\\\\\text{Percent of dissociation of trimethylacetic acid}=19.5%[/tex]
Hence, the percent of dissociation of trimethylacetic acid is 19.5 %
