It's strange the word "pH"
So, what is a notorious acidity, and how is it measured?
Imagine that we took a solution of a strong acid. This acid, in particular hydrochloric acid is (i.e. hydrogen chloride in water). HCl in contact with water is fully dissociated, i.e. splits into ions. Ie each particle of HCl in water gives one hydrogen ion (H +) and 1 chloride ion (Cl-). Imagine that the hydrochloric acid concentration was 1 mol / l (i.e. in 1 liter of a solution containing 1 mole of acid). This means that the concentration of hydrogen ions (or protons) is the same. If the concentration of hydrochloric acid was 0.1 mol / l, and then the concentration of protons is the same.
Slightly more complicated in the case of sulfuric acid. She, as you probably know, contains 2 hydrogen atoms (its formula H2SO4). In the sulfuric acid solution with a concentration of 1 mol / l concentration of protons will be 2 mol / L (after dissociation with one molecule of sulfuric acid, a hydrogen atom 2).
The proton concentration (ions H +) and determines the acidity of the medium. The higher it is, the more acidic environment. However, it so happened that in chemistry began to enjoy not only the concentration and negative logarithm of concentration.
What is a logarithm? Recall the construction of the power. For example, 10 2 = 10 * 10 = 100. Now we will try to solve the equation x 2 = 100. We know that to find x, it is necessary to take the square root of 100, and now we solve the equation x = 10 100. To find x, we must calculate the logarithm to the base ten hundred. Ie logarithm - is the degree to which you want to build a base to give the desired number. If the logarithm of the decimal, so the base is 10.
If the concentration is equal to 1, the logarithm of unity is zero. In fact, to get one, you want to raise ten to the power of 0 If the concentration is equal to 0.1, the logarithm is -1 (after 10 -1 = 0.1). However, the acidity was positive to the logarithm pririsovyvayut minus sign. Negative logarithm in physics and chemistry denoted by the letter p. Ie pH - it is simply the negative logarithm of hydrogen ion concentration (H +).
Of course, you may wonder what to do with the type of concentration 0.5 0.2 etc. To do this, there are scientific calculators which logarithm is denoted by an lg