Answer:The ratio of the concentrations of [tex]HA[/tex] and [tex]A^-[/tex] when the buffer has a pH of 7.02 is 0.69
Explanation:
The dissociation constant for formic acid = [tex]K_a=1.8\times 10^{-4}[/tex]
Concentration of HA= 0.5 mM
Concentration of [tex]A^-[/tex]= 0.1 mM
pH = 6.16
First we have to calculate the value of [tex]K_a[/tex].
Using Henderson Hesselbach equation :
[tex]pH=pK_a+\log \frac{[A^-}{[HA]}[/tex]
Now put all the given values in this expression, we get:
[tex]6.16=pK_a+\log (\frac{[0.1]}{0.5})[/tex]
[tex]pK_a=6.86[/tex]
To calculate the ratio of the concentrations of [tex]HA[/tex] and [tex]A^-[/tex] when the buffer has a pH of 7.02.
Using Henderson Hesselbach equation :
[tex]7.02=6.86+\log \frac{[A^-]}{[HA]}[/tex]
[tex]7.02=6.86+\log \frac{[A^-]}{[HA]}[/tex]
[tex]\frac{[A^-]}{[HA]}=1.44[/tex]
[tex]\frac{[HA]}{[A^-]}=0.69[/tex]
Thus the ratio of the concentrations of [tex]HA[/tex] and [tex]A^-[/tex] when the buffer has a pH of 7.02 is 0.69