In an acid-base titration, 0.1 M HCl solution was added to the NaOH solution of unknown strength. Which of the following correctly shows the change of pH of the titraction mixture in this experiment?
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Acid is added to base, so pH starts high and falls, with a sharp drop at the equivalence point.
The flask contains NaOH (strong base), so the initial pH is high (about 13). As 0.1 M HCl is added, pH decreases slowly, falls steeply near the equivalence point (pH 7), and then levels off at a low value approaching that of the acid. Graph (B) rises with volume, which is the curve for adding base to an acid, so it is wrong. Graph (D) shows a smooth exponential decay with no sharp equivalence-point jump. Graph (C) has an unphysical kink at the end. Graph (A) shows a high flat pH, a sharp fall, then a low flat pH, as required. In the printed option order, (A) is option (2). Answer: (2) (A)
