How to calculate a caption

How to calculate a caption

The caption is an expression of concentration of solution of substance, is used in analytical chemistry. Designates the mass of the dissolved substance in solution unit of volume. It is possible to determine a solution caption in analytical chemistry by a titrimetrichesky method.

It is required to you

- handle;
- note paper;
- calculator;
- Periodic Table (Mendeleyev's table).

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At the mentioned method volumes of two solutions which reacted among themselves, one of which – analyzed, and the second – a titrant or titrovanny solution - with known concentration are measured. For a titrant there is a concept of a conditional caption or caption on the defined substance. This amount of the analyzed substance, ottitrovanny 1 ml of solution. In a training course of chemistry there are some types of tasks on calculation of a caption of solution.

In the first type of tasks you will need to transfer concentration of solution from other units to a caption. Concentration is the relation of the size of the dissolved substance set by the weight, number of moles, volume to the size of solution or solvent. At the decision lean on that for definition of a caption from basic data it is necessary to receive the mass of the dissolved substance and size of volume of solution in which it is.

Example 1: define a caption of 15% of solution of sulfuric acid. Density of solution is 1,10 g/ml.
Concentration of solution is expressed in a mass fraction of substance. The mass fraction is the relation of mass of the dissolved substance and solution. Calculate the weight of one liter of solution - 1100 grams. Define the mass content of sulfuric acid in it: 1100*0,15=165g. Calculate a solution caption: 165 g / 1000 ml=0,165 g/ml.

Example 2: it is required to find a caption of 0,15 N of solution of sulfuric acid. The normality of solution is a quantity of an equivalent of the dissolved substance on solution liter, unit – mol-ekv/l. The equivalent is an amount of substance equivalent 1 I ask hydrogen ions in chemical reactions. One liter of solution contains 0,15 mol of an equivalent of sulfuric acid.

Using Mendeleyev's table, find the molar mass of H2SO4 – 98 g/mol. An equivalent of sulfuric acid – 1/2. Calculate the molar mass of an equivalent of H2SO4: 98/2=49 g/mol. Find, 0.15 mol of an equivalent of sulfuric acid how many weigh: 0,15*49=7,35 g.
Define a solution caption: 7,36 g / 1000мл=0,00736 g/ml.

It is necessary to find a conditional caption in the second type of tasks. For the decision calculate the mass of the dissolved substance and volume of solution with which it reacted from initial sizes.

Example 3: calculate a caption of solution of 0,1 N of AgNO3 solution on NaCl. Equivalents of AgNO3 and NaCl are equal to unit. Find the molar mass of NaCl — 58,5g/mol. Find amount of nitrate of silver in 1 ml of solution — 0,0001 mol. Therefore, amount of chloride of the sodium reacting with 1 ml of solution — 0,0001 mol. Increase the molar mass of NaCl by amount of substance and receive a conditional caption of solution of nitrate of silver — 0,000585 g/ml — the mass of NaCl reacting with 1ml AgNO3 solution.

The third type of tasks - on calculation of a caption of solution from the values received by a titrimetrichesky method. For their decision lean on the equation of reaction of the analysis. From it find, in what proportion of substance interact with each other.


Example 4: define a HCl solution caption if on neutralization of 20 ml of acid 18 ml 0,13 N of NaOH solution were required. Equivalents of HCl and NaOH are equal to unit. Find amount of chloride of sodium in 18 ml: 0,13*0,018=0,00234 mol. Therefore, the amount of the reacted hydrochloric acid too will be 0,00234 mol. Calculate the molar mass of HCl – 36,5 g/mol. Find the mass of the received amount of hydrochloric acid: 0,00234*36,5=0,08541 g. This mass of substance contains in 20 ml of solution. Find a solution caption: 0,08541/20=0,0042705 g/ml.