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Calculate the Ka for a 0.50M weak acid solution that has a pH equal to 4.15.2.33 x 10-93.21 x 10-71.00 x 10-87.59 x 10-8

Question

Calculate the Ka for a 0.50M weak acid solution that has a pH equal to 4.15.

Options:

  1. 2.33 x 10^-9
  2. 3.21 x 10^-7
  3. 1.00 x 10^-8
  4. 7.59 x 10^-8
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Solution

The question seems to be a bit jumbled, but I'll try to provide a general method for calculating the Ka (acid dissociation constant) for a weak acid solution given its molarity and pH.

  1. First, you need to know the pH of the solution. In your case, it's given as 4.15.

  2. The pH is the negative logarithm of the concentration of H+ ions in the solution. So, to find the concentration of H+ ions, you would use the formula: [H+] = 10^(-pH). In this case, [H+] = 10^(-4.15).

  3. The Ka expression for a weak acid HA dissociating into H+ and A- is Ka = [H+][A-]/[HA]. In a weak acid solution at equilibrium, the concentrations of H+ and A- are equal, so the expression simplifies to Ka = [H+]^2/[HA].

  4. You're given that the initial concentration of the weak acid [HA] is 0.50M. After dissociation, the concentration of HA decreases by x, and the concentrations of H+ and A- each increase by x. Since [H+] = [A-] = x, and x is small compared to 0.50M (because the acid is weak and doesn't dissociate much), you can approximate [HA] as 0.50M.

  5. Substituting these values into the Ka expression gives Ka = (10^(-4.15))^2/0.50.

  6. Calculate this expression to find the Ka of the weak acid.

Please note that the numbers you provided after the pH value (2.33 x 10-93.21 x 10-71.00 x 10-87.59 x 10-8) are not clear in their purpose and so have not been used in this calculation. If they are relevant to the question, please provide more context.

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