Michael C. answered • 01/24/23
Focus on understanding rather than memorization
The first step to tackling this problem is understanding what is given and what is being asked for. The question stem gives us a buffer solution, with the concentration of the acid and its conjugate base and is asking us to find the solutions pH. When a question stem mentions pH, pKa, and or buffer solutions, the first equation in your mind should be the Henderson-Hassebalch equation.
pH = pKa + log( [A-]/[[HA] )
A key detail to remember here is what is the conjugate base and what is the acid. Since sodium acetate is a salt, we know that acetate is an anion (has a negative charge) and will be our conjugate base. This is because once acetic acids fulfills its role as an acid (donating a proton) it will carry a negative charge.
Now that we have these details figured out, we can plug in the values into our equation and solve:
pH = 4.75 + log ( 1M / .5M ) = 4.75 + .3 = 5.05
