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:
- 2.33 x 10^-9
- 3.21 x 10^-7
- 1.00 x 10^-8
- 7.59 x 10^-8
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.
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First, you need to know the pH of the solution. In your case, it's given as 4.15.
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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).
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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].
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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.
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Substituting these values into the Ka expression gives Ka = (10^(-4.15))^2/0.50.
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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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