Instruction

1

Read carefully the task. Briefly on the left side of the page, record the data using letter symbols and formulas of chemicals, if any. Identify the problem that needs to be found.

2

Write down on the right side of the sheet a General formula for the mass fraction of the solute

ω = m1 / m,

where m1 is the mass of the solute, and m the mass of the entire solution.

If the content of the mass fraction of solute need to find the percentage, multiply the resulting number by 100%:

ω = m1 / m x 100%

ω = m1 / m,

where m1 is the mass of the solute, and m the mass of the entire solution.

If the content of the mass fraction of solute need to find the percentage, multiply the resulting number by 100%:

ω = m1 / m x 100%

3

In applications where the need to calculate the mass fraction of each of the elements included in the chemical substance, use the table of D. I. Mendeleev. For example, find the mass fraction of each of the elements included in the composition of the hydrocarbon, formula C6H12 which

m (C6H12) = 6 x 12 + 12 x 1= 84 g/mol

ω (C) = 6 m1(C) / m (C6H12) x 100% = 6 x 12 g / 84 g/mol x 100% = 85%

ω (N) = 12 m1(N) / m (C6H12) x 100% = 12 x 1 g / 84 g/mol x 100% = 15%

m (C6H12) = 6 x 12 + 12 x 1= 84 g/mol

ω (C) = 6 m1(C) / m (C6H12) x 100% = 6 x 12 g / 84 g/mol x 100% = 85%

ω (N) = 12 m1(N) / m (C6H12) x 100% = 12 x 1 g / 84 g/mol x 100% = 15%

4

Write down the answer to the problem.

Useful advice

The problem of finding the mass fraction of a material after evaporation, dilution, concentration, mixing the solutions solve using the formulas derived from the definition of mass fraction. For example, a task on evaporation can be solved by using this formula

ω 2= m1 / (m – Dm) = (ω 1• m) / (m – Dm) 2 where ω is the mass fraction of the evaporated substance in solution, Dm is the difference between the masses before and after heating.

ω 2= m1 / (m – Dm) = (ω 1• m) / (m – Dm) 2 where ω is the mass fraction of the evaporated substance in solution, Dm is the difference between the masses before and after heating.

# Advice 2 : How to calculate mass percentage

Mass fraction is the percentage of a component in a mixture or an element in the substance. Tasks for the calculation of the mass fraction of face not only schoolchildren and students. The ability to calculate the percentage concentration of the substance finds very practical application in real life - where required, preparation of solutions, ranging from construction to cooking.

You will need

- - the periodic table;
- formula to calculate the mass fraction.

Instruction

1

Calculate the mass

**fraction**by definition. As the mass of the substance consists of masses of elements that compose it, then**share**any item you have some of the mass of a substance. The mass fraction of the solution is equal to the ratio of the mass solute to the mass of the entire solution.2

The mass of solution is equal to the sum of the masses of the solvent (usually water) and substances. The mass fraction of the mixture is equal to the ratio of the mass of a substance to the weight of the mixture containing the substance. Multiply the result by 100%.

3

Find the mass

**percentage**yield using the formula ω=MD/MP, where MP and MD - value is estimated and obtained actual output of matter (mass), respectively. Calculate the estimated weight of the reaction equations, using the formula m=nM, where n is the chemical amount of substance, M is the molar mass of the substance (the sum of the atomic masses of all the elements in a substance), or formula m=Vρ, where V is the volume of the substance, ρ is its density. Number substances in turn if necessary, replace the formula n=V/Vm or also find from the equation of the reaction.4

Mass

**fraction**of element in compound calculate using the periodic table. Fold the atomic masses of all elements in the substance, if necessary damnosa on indices. You will get the molar mass of the substance. Find the molar mass of an element from the periodic table. Calculate the mass**percentage**by dividing the molar mass of the element by the molar mass of the substance. Multiply by 100%.Useful advice

Pay attention to the physical process, which is the place to be. By evaporation do not count mass fraction as solution (water or other liquid) no. Don't forget that with the concentration, otherwise called a partial evaporation, the mass fraction of a substance is increased. If you dilute a concentrated solution, the mass fraction decreases.