Final answer:
To calculate the Ka value, use the pH of the solution and the known concentration of the weak acid, HNO₂. Calculate the concentration of H₃O⁺ using the pH value, and then use that concentration to calculate the Ka value using the formula Ka = ([H₃O⁺][NO₂⁻]) / [HNO₂].
Step-by-step explanation:
To calculate the Ka value, we need to use the pH of the solution and the known concentration of the weak acid, HNO₂. From the given information, the pH is 3.28. To find the concentration of H₃O⁺, we can take the logarithm of the inverse of the pH value:
[H₃O⁺] = 10^(-pH)
Once we have the concentration of H₃O⁺, we can use it to calculate the Ka value using the formula:
Ka = ([H₃O⁺][NO₂⁻]) / [HNO₂]