2.Glycolic acid is often used in “facial peels” and has a Ka of 1.5x10^-4. If a movie star is to have a solution of pH 2.1 applied to her face at night, what concentration of glycolic acid solution should be made up (assuming that it is a monoprotic acid, and that it dissolves freely in water)
HG ==> H^+ + G^-
Ka = (H^+)(G^-)/)HG) = 1.5 x 10^-4
Convert pH 2.1 to (H^+), substitute into Ka expression for (H^+) and (G^-) and solve for (HG). That will give you concn HG in moles/L.
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To determine the concentration of the glycolic acid solution, we need to use the formula for the acidity constant (Ka):
Ka = [H+][A-] / [HA]
Where [H+] represents the concentration of hydrogen ions (protons), [A-] represents the concentration of the conjugate base (glycolate anion in this case), and [HA] represents the concentration of the acid (glycolic acid). Since glycolic acid is a monoprotic acid, the concentration of hydrogen ions will be the same as the concentration of glycolic acid.
Given that the pH of the solution is 2.1, we can determine the concentration of hydrogen ions using the formula:
pH = -log[H+]
2.1 = -log[H+]
Taking the antilog of both sides:
[H+] = 10^(-pH)
[H+] = 10^(-2.1)
[H+] ≈ 7.943 x 10^(-3) M
Since the concentration of hydrogen ions is equal to the concentration of glycolic acid, the concentration of glycolic acid should be approximately 7.943 x 10^(-3) M.