Calculate the pH of a solution that is 0.295 M in sodium formate (NaHCO₂) and 0.205 M in formic acid (HCO₂H). The K_aof formic acid is 1.77 × 10^-⁴. A) 4.963 B) 13.84 C) 10.10 D) 3.903 E) 3.587

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Formic acid is a weak acid, and when it is dissolved in water, it partially dissociates to give formate ions and hydronium ions. The balanced equation for this dissociation reaction is: HCO₂H + H2O ⇌ H3O+ + CO₂ The acid dissociation constant (Ka) for this reaction can be used to calculate the pH of the solution using the following formula: pH = -log[H3O+] Ka for formic acid is given as 1.77 × 10^-⁴. We can use this value to calculate the concentration of hydronium ions in the solution, which is necessary for finding the pH. The Ka expression is: Ka = [H3O+][CO₂-]/[HCO₂H] At equilibrium, the concentrations of formate and hydronium ions are equal to each other, i.e. [CO₂-] = [H3O+]. If x is the concentration of hydronium ions that result from the dissociation of formic acid, then the concentrations of formic acid and formate ions can be expressed as (0.205 - x) and (0.295 + x), respectively. Plugging these concentrations into the Ka expression and solving for x, we get: 1.77 × 10^-⁴ = x^2/(0.205 - x) x = 0.0136 M (to 3 significant figures) Therefore, the pH of the solution is: pH = -log(0.0136) = 3.903

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