Mathematical deduction ... this uses mathematics, but pH mutation is determined by the principle of analytical chemistry.

Firstly, it is clear that pH is the negative logarithm of [H]+ (hydrogen ion concentration), and pH= 1 means it is-1 power mol/L (that is, 0. 1 mol/L), and pH=7 is 10.

In analytical chemistry, the error of 0. 1% is acceptable, that is, the actual measuring point is 99.9%- 100. 1%. You can calculate it according to this titration range. For example, titrate 20 ml of 0. 1 mol/L sodium hydroxide (NaOH).

Well, you can try to calculate and draw a titration curve with NaOH dosage as abscissa and pH as ordinate. You will find that the pH value of the first 18mL (90% dosage) only changed by 1.28, and the pH value of the next 1.8mL, that is, 9% (total 19.8ml, 99%) changed again. The change is small. Then add 0. 18mL, that is, 0.9% (the total amount is 19.98mL, 99.9%, which can be regarded as the end point of the first measurement, and the error is -0. 1%, that is, the lower limit of the error), and the pH change is 1.0. Next,

The next 0. 1% (the total amount is 100%, the stoichiometric point), and the pH=7 is changed from 4.3 to 7.0, and then 0. 1% (the total amount is 100. 1%, the upper limit of error, and.

So the errors of 4.3-9.7 are all less than 0. 1%, which is the allowable error of analytical chemistry, and this range is the titration end point.

Because the pH value changes greatly near the stoichiometric point, it is called pH mutation.

Other titrations also have this mutation.