To determine the concentration of an acid in an aqueous solution, an acid-base titration is commonly performed. A strong base solution with a known concentration, usually NaOH or KOH, is added to neutralize the acid solution according to the color change of the indicator with the amount of base added.[7] The titration curve of an acid titrated by a base has two axes, with the base volume on the x-axis and the solution's pH value on the y-axis. The pH of the solution always goes up as the base is added to the solution.
Sam was looking over his notes from his science experiment. He looked at the graph he had made while titrating an acid with a base.  He noticed that on the first day there was less base in the acid and the ph was lower. On the second day he added more base and the y-axis on his graph increased.
Was the x-axis increased or decreased the second day.