2. Use fresh and pollution-free distilled water;
3. use a class A or class B 250ml volumetric flask, pour a small amount of distillation into the standard material bag, dissolve it and pour it into the volumetric flask;
4. Wash the standard material bag several times with a small amount of distilled water, and pour the residual liquid into the volumetric flask;
5. Add distilled water to the volumetric flask to 250 ml, shake it several times repeatedly, and put it for a few hours before it can be used.
Explanation of PH value nouns:
PH value, also known as hydrogen ion concentration index and pH value, is a scale of hydrogen ion activity in solution, which is also a measure of acid-base degree of solution in the usual sense. This concept is 1909 by Danish biochemist s? ren Peter Lauritz S? Rensen proposed. P stands for German Potenz, which means strength or concentration, and H stands for hydrogen ion (H). Sometimes pH is also written as pondus hydrogenii in Latin.
Under normal circumstances (around 25℃ and 298K), when pH <: 7, the solution is acidic, and when pH >; 7, the solution is alkaline, and when pH=7, the solution is neutral.
Note: The pH value is allowed to be less than 0, for example, the pH of hydrochloric acid (10 mol/L) is-1.
computing formula
The calculation formula of pH value is as follows:
Where [H] refers to the activity of hydrogen ions in solution (sometimes also written as [H3O], hydronium ion activity), and the unit is mole/liter. In dilute solution, the activity of hydrogen ions is approximately equal to the concentration of hydrogen ions, which can be used for approximate calculation.
At standard temperature and pressure, the aqueous solution with pH=7 (such as pure water) is neutral, because the product of the concentration of hydrogen ions and hydroxyl ions naturally ionized by water at standard temperature and pressure (ion product constant of water) is always1×1kloc-0/4, and the concentrations of both ions are14. PH less than 7 means that the concentration of H is greater than that of OH, so the solution is acidic, while pH greater than 7 means that the concentration of H is less than that of OH, so the solution is alkaline. Therefore, the smaller the pH value, the stronger the acidity of the solution; The greater the pH, the stronger the alkalinity of the solution.
Under the condition of non-aqueous solution or non-standard temperature and pressure, pH=7 may not mean that the solution is neutral, which needs to be determined by calculating the ionization constant of the solvent under this condition. For example, at the temperature of 373K( 100℃), pH=6 is a neutral solution.