Anonymous
Anonymous asked in Science & MathematicsChemistry · 5 months ago

Chemistry Question (URGENT)?

The acid dissociation constant, Ka is more suitable than the pH of the acid solution as a measure of the strength of an acid although both value may be used to represent its acidity. Explain by using chemical equation or ionic equation.

1 Answer

Relevance
  • 5 months ago
    Best answer

    pH vs Ka .....

    The pH of a solution is essentially a measure of the concentration of the hydrogen ions. The concentration of H+ can be "all over the map" regardless of whether the acid is strong or weak. The pH is simply the H+ concentration.

    .... pH = -log[H+]

    The Ka of an acid shows the degree to which an acid ionizes in water. The greater the value of Ka, the greater the degree of ionization. Acids with large values of Ka are strong acids and ionize completely. Weak acids have Ka values less that 1. Weak acids are only partially ionized. Be sure to understand the difference between "strong" and "weak" as it applies to acids and bases. Strong acids and bases ionize completely. Weak acids and bases ionize partially. "Strong" and "weak" do not refer to concentration.

    HCl(aq) --> H+ + Cl- ......... HCl is a strong acid ........ Ka is large

    0.02M ........0 ...... 0 ........... before ionization

    ...0........0.02M ...0.02M ..... after ionization

    HC2H3O2 --> H+ + C2H3O2^- ........ acetic acid is a weak acid, Ka = 1.76x10^-5

    1.00M ............0 ...........0 .................. before ionization

    1.00M ........ 0.0042 ...0.0042M ........ after ionization

    Notice that even though acetic acid is more concentrated than 0.02M HCl, the concentration of H+ is greater for the HCl solution than the acetic acid solution. The pH told us nothing about how strong or weak the acids are.

Still have questions? Get answers by asking now.