Titration analysis method-acid-base titration (2)

2.

To use acid-base titration for analysis and determination, it is necessary to understand the change law of pH value during the acid-base titration process, especially the change of pH value near the stoichiometric point, so that it is possible to select the appropriate indicator and accurately determine the titration end point

The curve that represents the change of pH value during the titration is called the acid-base titration curve

This type of titration includes the mutual titration of HCI, H ₂ SO ₄ and NaOH, KOH, etc.

Now take the 0.

Table 2.

In order to show the change trend of pH value in the titration process more intuitively, plot the pH value of the solution against the added amount of NaOH or the percentage of titration to obtain an S-shaped titration curve as shown in Figure 2.

Figure 2.

The reason why the pH value changes in an S-shaped curve during the titration is that: at the beginning, the amount of acid in the solution is large, and the addition of 90% NaOH solution changes the pH value by 1.

The most practical part of the S-shaped curve is the titration jump range before and after the stoichiometric point, which provides the possibility for the choice of indicator.

In order to select the indicator in a larger range, generally the wider the jump range of the titration curve, the better

Figure 2.