Problem description:
What is the PH value of vinegar? Recently, some people say that vinegar is alkaline, please consult.
Analysis:
PH value: vinegar 2.9
pH value
PH value, also known as hydrogen ion concentration index, is a measure of hydrogen ion activity in solution and also a measure of acid-base degree of solution in general sense. This concept is Danish biochemist S? Len Peter Laurits's? Renson proposed. P stands for German potenz, which means strength or concentration, and H stands for hydrogen ion (H+). Sometimes pH is also written in Latin as pondus hydrogenii.
Generally speaking, the pH value is a number between 0 and 14. When pH; 7, the solution is alkaline, when pH=7, the solution is neutral.
definition
The pH value of some common substances.
Acid solution of lead-acid battery
Gastric acid 2.0
Lemon juice 2.4
Coke 2.5
Vinegar 2.9
Orange juice or apple juice 3.5
Beer costs ￡ 4.50
Coffee 5.0
Tea 5.5
acid rain
Saliva of cancer patients 4.5-5.7
Milk 6.5
Pure water 7.0
Saliva of healthy people 6.5-7.4
Blood 7.34-7.45
Seawater 8.0
Hand sanitizer 9.0- 10.0
Household ammonia detergent 1 1.5
Bleach 12.5
Household lye 13.5
Whether it is acidic or alkaline, you can calculate it yourself by the following methods:
The calculation formula of pH value is as follows:
Where [H+] refers to the activity of hydrogen ions in solution (sometimes 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 approximately calculated.
At standard temperature and pressure, aqueous solution with pH=7 (such as pure water) is neutral, because the concentrations of hydrogen ions and hydroxyl ions naturally ionized by water at standard temperature and pressure are 1× 10-7. A small pH value means that the solution is acidic, while an increase in pH value means that the solution is alkaline.
Usually, the pH value of the aqueous solution we see is between 0 and 14, but for the non-aqueous solution system or strong acid and alkali, the pH value may be less than 0 or greater than 14.
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 a temperature of 373k( 100℃), pH=6 is a neutral solution.
measure
There are many ways to measure the pH value of a solution:
When pH indicator is added to the solution to be tested, different indicators will change color according to different pH values, and the range of pH value can be determined according to the study of indicators. When titrating, an accurate pH standard can be made.
Use pH test paper, including a lot of test paper and precision test paper. Dip a little solution to be tested on the test paper with a glass rod, and then get the pH value of the solution according to the color change of the test paper and the comparison with the colorimetric chart. The above table is equivalent to a color chart.
Use a pH meter, which is an instrument for measuring the pH value of a solution. It measures the pH value of the solution through a pH selective electrode (such as a glass electrode). The acidity meter can be accurate to two decimal places.
Tired
POH is a concept corresponding to pH, indicating the activity of hydroxyl ions in solution, and its definition is as follows:
At 298k(25℃), the ionic product of water KW = [H+] [OH-] =10-14. Because logkw = log [h+]+log [oh-], pOH= 14-pH at this time.
App application
According to the definition of pH value, pH value is a measure of the acidity and alkalinity of the solution, which needs to be controlled in many ways. These places need to know the pH value of the solution:
In medicine, the pH value of human blood is usually between 7.35 and 7.45. If it fluctuates, it is a pathological phenomenon. The pH value of saliva is also used to judge the condition.
Chemistry and chemical engineering: Many chemical reactions need to be carried out at a specific pH value, otherwise the expected products cannot be obtained.
Agriculture: Many plants have the habit of liking acidic soil or alkaline soil, such as tea planting. Controlling the pH value of soil can make the planted plants grow better.