PH describes the pH of the aqueous solution, and is expressed by pH. Under the thermodynamic standard conditions, the aqueous solution with pH=7 is neutral, pH; 7 cases were alkaline.

The pH range is 0~ 14, which is only suitable for dilute solution. The pH value of the solution with hydrogen ion concentration or hydroxide ion concentration greater than 1mol/L is directly expressed by concentration.

Measure the pH value of the solution:

Add a pH indicator to the solution to be tested. According to different pH values, different indicators will change color. For example, if an acidic solution is dropped into litmus test solution, litmus test solution will turn red. When alkaline solution is dropped into litmus test solution, litmus test solution will turn blue (litmus test solution will not change color when it meets neutral liquid). By studying the indicator, the range of pH value can be determined.

Dropping colorless phenolphthalein solution into acidic or neutral solution will not change color; Dropping colorless phenolphthalein solution into alkaline solution will turn red. When adding pH indicator to the colored solution to be tested, the pH indicator that can produce obvious color difference should be selected.