Helllo I have been given the following question. I have been able to work out all the concentration needed to substitute in to the Ka equation expect for the [A-]. I know that it’s mols is equal to the mols of KOH (0.0604 mols) but I do not know how to go from its mols to its concentration. In the mark scheme they have multiplied the mols by 4 to get the concentration as 0.242. But where is the 4 coming from? I only need help with the conjugate salt ion concentration.
“A buffer solution is prepared by dissolving 3.39g of potassium hydroxide in 250 cm² of 0.376 moldm-3 butanoic acid. This buffer solution has a pH of 5.07 at 25°C.
Calculate the acid dissociation constant, Ka, of butanoic acid at 25 °C. Assume that the volume of the solution remains constant at 250 cm-3 when the potassium hydroxide is dissolved”