The most simple and obvious method (though not very accurate) is to use special test strips that you can buy in the store. We need to put on a strip a drop of acid and after a while to compare the color and intensity of the developed color with the samples indicated on the package. The brighter, vivid red color will be in the sample, the stronger the acid, and Vice versa.
If there is no indicator paper or need a more accurate result, then come to the aid of "the dissociation constant", that is a measure of the ability of a substance (in this case, acid) to break down into ions in aqueous solution. Acids dissociate into a hydrogen cation (proton) and an anion acid residue. The higher this value is, i.e. the more ionic the collapse proceeds, the stronger the acid. Dissociation constants of most acids can be found in any chemical Handbook.
Note that for polybasic acids (e.g. sulphuric, carbonic, phosphoric and others), dissociation which takes place in several stages, operate with different constants for each stage of dissociation.
The acid strength can also be determined by how occur some chemical reaction. For example, if you mix hydrochloric acid with phosphate of potassium, it forms potassium chloride and phosphoric acid. If you mix sulphuric acid with carbonate of sodium, the formed sodium sulfate and carbonic acid (which is so unstable that immediately disintegrate into water and carbon dioxide). In fact, and in another case more strong acids (hydrochloric and sulphuric) have displaced the weaker (phosphate and coal) from their salts. This rule is universal: strong acid displaces the weak always from its salts.
Advice 2 : How to determine the degree of oxidation of a substance
The degree of oxidation , the conditional charge of the atom in the compound, calculated on the assumption that it consists only of ions. Some elements have a constant degree of oxidation, while others are able to change it. In order to identify substances having different connections, different values will use a special algorithm.
The degree of oxidation is written above the symbol of the element, the stitch sign is placed, and then the value. It can be negative, positive or equal to zero. The sum of all degrees of oxidation in the substance is equal to zero. Some substances have a constant degree of oxidation for all compounds. For example, in metals it is always positive and equal to their valency (ability to attach or to replace a certain number of atoms or groups of atoms). The alkali metals have a degree of oxidation of +1, while alkaline earth is +2. Hydrogen always has a degree of oxidation of +1, except the hydrides, there is -1 (for example, KH(-1)). The degree of oxidation of the oxygen equal to -2 exceptions: peroxide (BaO2(-1)) and fluoride oxygen(O(+2)F). Fluorine always has -1(DQ(-1)).
If the substance consists of one or more atoms of the same name, i.e. it is simple, its degree of oxidation equal to zero. For example, H2, Ag, O2, Na, etc.
Complex substance in the first place set value of the degree of oxidation of the elements, which it is not changed. Then we make an equation with one unknown, i.e. the degree of oxidationthat you need to find, denoted by X. for Solve this equation, we obtain the desired value. It should be noted that in the presence of a complex substance of several atoms of the same element, the degree of oxidation in the preparation of the equations is multiplied by the number of items. Consider the examples.
If you need to find the degree of oxidation of sulphur in the substance Na2SO4 doing so: first, we arrange the known values are Na(+1)2SO(-2)4. We denote the degree of oxidation of sulfur for X, we write the equation, remembering about the fact that the sum of all the degree of oxidation is always zero: 2+X-8 = 0. Solve: X = 8-2 = +6. Therefore, the degree of oxidation of sulfur is +6.
Another example: AgNO3. Place: Ag(+1)NO(-2)3. We obtain the equation: 1+X-6 = 0. Calculated: X = 6-1 = +5. The desired value is found.
The degree of oxidation can have fractional values, for example in magnetic iron ore Fe2O3 is +8/3.