c= 1.4 X [tex]10^-^4[/tex] is the composition and ph of an ideal buffer prepared from lactic acid ([tex]CH_3CHOHCO_2H[/tex]), where the hydrogen atom highlighted in boldface is the acidic hydrogen atom.
A buffer is a solution that can resist pH change upon the addition of an acidic or basic components.
Equilibrium equation
[tex]C_3H_6O_3[/tex] ⇄[tex]C_3H_5O_3^-[/tex] +[tex]H^+[/tex]
Assuming a degree of dissociation [tex]\alpha[/tex] =[tex]\frac{1}{10}[/tex]
And the initial concentration of [tex]C_3H_6O_3[/tex] =c
At equlibrium ;
Concentration of [tex]C_3H_6O_3[/tex] = [tex]c - c\alpha[/tex]
[tex]C_3H_5O_3^-[/tex] = [tex]c\alpha[/tex]
[[tex]H^+[/tex]] = [tex]c\alpha[/tex]
[tex]Ka =\frac{c\alpha X c\alpha }{c-c\alpha }[/tex]
[tex]\alpha[/tex] is very small so 1-[tex]\alpha[/tex] can be neglected and the equation is;
[tex]Ka = c\alpha X \alpha[/tex]
[H^+] = [tex]c\alpha[/tex] =[tex]\frac{k\alpha }{\alpha }[/tex]
pH = -log [[tex]H^+[/tex]]
pH = -log[tex]Ka[/tex] +log [tex]\alpha[/tex]
[tex]Ka[/tex] = 1.38 X [tex]10^{-4}[/tex]
[tex]\alpha[/tex] = [tex]\frac{1}{10}[/tex]
pH = 3.86 -1
pH =2.86
Composition ;
C=[tex]\frac{1}{\alpha }[/tex] X [tex][H^+][/tex]
[tex][H^+][/tex] =0.0014
c= 0.0014 X [tex]\frac{1}{10}[/tex]
c= 1.4 X [tex]10^-^4[/tex]
Hence, c= 1.4 X [tex]10^-^4[/tex] is the composition and ph of an ideal buffer prepared from lactic acid ([tex]CH_3CHOHCO_2H[/tex]), where the hydrogen atom highlighted in boldface is the acidic hydrogen atom.
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