(1) neutral solution, pH = 7；;
(2) acidic solution, pH < 7, the smaller the pH value, the stronger the acidity;
(3) alkaline solution, pH > 7, the greater the pH value, the stronger the alkalinity.
Please pay attention to the following when using pH test paper:
The test paper should not be directly inserted into the solution.
The pH of concentrated sulfuric acid can't be measured by test paper.
The test paper shall not touch the test tube mouth, bottle mouth, catheter mouth, etc.
When determining the pH value of the solution, the test paper should not be wetted with distilled water in advance, because wetting the test paper is equivalent to diluting the tested solution, which will lead to inaccurate measurement. The correct method is to drop a glass rod soaked in the solution to be tested in the middle of the test paper. After the test paper changes color, compare it with the standard colorimetric card to determine the pH value of the solution.
After taking out the test paper, the container containing the test paper should be tightly covered to avoid being polluted by some gases in the laboratory.
It must be used at room temperature, otherwise it will lead to inaccurate results.