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The pH is an acronym that stands for hydrogen potential, and works as a measure of the acidity or alkalinity of a dissolution, indicating the concentration of hydronium ions present in a solution.
It is shown that there is a complete correlation between the concentration of the hydrogen ions and the level of acidity of a substanceStrong acids have high concentrations of hydrogen ions, while weak acids have low concentrations.
Mathematically, the pH is defined as the decimal logarithm of the reciprocal of the activity of the hydrogen ion in a solution. The logarithm operation is used to linearize the trend, so that the number has a meaning in itself. The scale was introduced by the chemist Sorenson, who gave the scale its name until 1924.
The pH scale is set between the number 0 and 14: 0 is the acid end, while 14 is the alkaline end. The number 7, the intermediate, is what is known as neutral pH.
As measured?
For pH measurement, an easy-to-use chemical is often used, which is Litmus paper. It is a role that it changes its color depending on the solution in which it is immersed.
The most acidic substances will cause the paper to turn pink, while the most basic ones will cause it to turn blue. Some of the papers of this type have level markings, so that whoever uses it can decode the hydrogen potential level simply with color.
However, the role of Litmus is not completely effective, and in cases where it is not effective, a device known as pH meter, a sensor used in the chemical method to measure the pH of a solution. There, a cell for pH measurement consists of a pair of electrodes, one made of calomel and the other made of glass: this meter is a very sensitive voltmeter, and the electrodes connected to it will generate an electric current when immersed in solutions.
Examples of the pH of certain substances
| Lemon juice (pH 2) | Orange juice (pH 4) |
| Gastric juice (pH 1) | Beer (pH 5) |
| Detergent (pH 10.5) | Ammonia (pH 12) |
| Soapy water (pH 9) | Bleach (pH 13) |
| Sea water (pH 8) | Cola soft drink (pH 3) |
| Lime water (pH 11) | Hydrochloric acid (pH 0) |
| Milk of Magnesia (pH 10) | Battery (pH 1) |
| Human skin (pH 5.5) | Sodium hydroxide (pH 14) |
| Milk (pH 6) | Pure water (pH 7) |
| Vinegar (pH 3) | Blood (pH 8) |
How to keep the pH constant?
Sometimes the laboratory procedure requires preparing and storing a solution with constant pH. The preservation of this solution is more difficult than its preparation, because if it comes into contact with air it will absorb carbon dioxide and it will become more acidic, while if it is stored in a glass container it will become more alkaline due to the effect of impurities. detached from the glass.
The buffer solutions are those capable of keeping their pH stable against the addition of relatively small amounts of acids or bases powerful.
Solutions of this type are prepared with a weak acid and a salt of the same acid, or by using a weak base and a salt of the same base. Even cells in living organisms must maintain an almost constant pH, for the enzymatic action and metabolic.
It can serve you: Examples of Acids and Bases
