Acid-base titration is a titration analysis method based on proton transfer reaction between acid and alkali in water. It can be used to determine acid, alkali and amphoteric substances, and it is a method for capacity analysis through acid-base reaction. Using acid as titrant can determine alkali, and using alkali as titrant can determine acid, which is a very widely used analytical method. The most commonly used acid standard solution is hydrochloric acid, and sometimes nitric acid and sulfuric acid are also used. The reference substance for calibrating them is sodium carbonate.

As can be seen from the titration curve:

(1) Only alkaline indicators (phenolphthalein or thymolphthalein, etc. ) and indicators that change color in the acidic range (such as methyl orange, methyl red, etc.). ) cannot be selected. Because the jump range is small, the pH value is between 7.75 and 9.70; The metering point is in the alkaline zone.

(2) The accurate judgment of weak acid titration is C Ka >；; 10-8。 Because the bigger the Ka, the larger the jump range. Ka < At 10-8, however, has no obvious jump, so it is impossible to determine the end point with indicators; In addition, the greater the concentration of acid, the greater the jump.