in relating y = mx + b to the Henderson Hasselbach equation - p H = pK a+ log[A][HA] what is the slope ?

1. in relating y = mx + b to the Henderson Hasselbach equation - pH = pKa + log [A][HA]

what is the slope ? is it pKa or log{A/HA]

THIS is the original question

1. On a single graph, plot the initial pH as a function of base:acid molar ratio for both of the buffer systems (Acetic Acid/Acetate and Ammonium chloride/Ammonia). The initial pH is the pH measured for each solutions with the acid:base volume ratios 1:1, 4:1, 9:1, 1:4, 1:9 before any HCl or NaOH was added. Make a separate graph of initial pH as a function of the base-10 log of the molar ratio. Both buffer systems should be on the same axes. (Hint: it would be useful to setup the molar ratio as x = moles of base / moles of acid.) Which plot has a linear relationship? What is the slope of this line? Relate this to the Henderson-Hasselbach equation.