Determination of the mass fraction of each substance in solution. The task of calculating the mass fraction of a substance in solution

The shares of the dissolved substance
ω \u003d m1 / m,
where M1 is the mass of the dissolved substance, and M is the mass of the whole solution.

If the mass fraction of the dissolved substance is needed, multiply the resulting number is 100%:
ω \u003d m1 / m x 100%

In tasks where you need to calculate the mass fractions of each of the elements included in the chemical, use Table D.I. Mendeleeva. For example, find out the mass fractions of each of the elements that are part of the hydrocarbon, which C6H12

m (C6H12) \u003d 6 x 12 + 12 x 1 \u003d 84 g / mol
Ω (C) \u003d 6 m1 (C) / M (C6H12) x 100% \u003d 6 x 12 g / 84 g / mol x 100% \u003d 85%
ω (H) \u003d 12 m1 (H) / M (C6H12) x 100% \u003d 12 x 1 g / 84 g / mol x 100% \u003d 15%

Helpful advice

Tasks for finding a mass fraction of substances after evaporation, dilution, concentration, mixing solutions solve using formulas derived from a mass fraction. For example, the task of evaporation can be solved using such a formula
ω 2 \u003d M1 / \u200b\u200b(M - Dm) \u003d (Ω 1 m) / (m - Dm), where ω 2 is a mass fraction of a substance in a fallen solution, DM is the difference between the masses before heating and after.

Sources:

• how to determine the mass fraction of the substance

There are situations when it is necessary to calculate mass liquidscontained in any container. It may be during training in the laboratory, and during the decision of the household problem, for example, during repair or painting.

Instruction

The easiest method is to resort to weighing. First weigh the container together with, then break the fluid into another container suitable, and weigh the empty container. And then it remains only to deduct from the greater value, and you will receive. Of course, it is possible to resort to this way, only dealing with the unusual liquids, which, after overflow, almost do not remain on the walls and the bottom of the first container. That is, it will remain the amount and then, but it will be so small that they can be neglected, it will not affect the accuracy of calculations.

And if the liquid is viscous, for example,? Like it then mass? In this case, you need to know its density (ρ) and the volume occupied (V). And then everything is already elementary. The mass (M) is calculated according to m \u003d ρv. Of course, before calculating, it is necessary to translate the factors into a single system of units.

Density liquids Can be found in the physical or chemical directory. But it is better to use the measuring instrument - a denseter (densitometer). And the volume can be calculated, knowing the shape and dimensions of the container (if it has a proper geometric shape). For example, if the same glycerin is in a cylindrical barrel with the base diameter D and height H, then the volume

ATTENTION!!!

Students 9 classes !!!

For the successful surcharge of the Chemistry Exam in some tickets you will need to solve the task. We invite you to consider, disassemble and consolidate in memory the solution of typical tasks in chemistry.

The problem of calculating the mass fraction of a substance in solution.

In 150 g of water was dissolved 50g phosphoric acid. Find a mass fraction of acid in the resulting solution.

Dano: M (H2O) \u003d 150g, M (H3PO4) \u003d 50g

To find : W (H3PO4) -?

Getting to solve the problem.

Decision: one). We find a mass of the resulting solution. To do this, simply lay water and the mass of phosphoric acid adhered to it.

m (solution) \u003d 150g + 50 g \u003d 200 g

2). To solve, we need to know the formula of the mass share. We write on the formula of the mass fraction of the substance in solution.

w. (substances) \u003dhttps://pandia.ru/text/78/038/images/image002_9.png "width \u003d" 19 "height \u003d" 28 src \u003d "\u003e * 100% \u003d 25%

Record the answer.

Answer: w (H3PO4) \u003d 25%

The task of calculating the amount of substance of one of the reaction products, if the mass of the starting material is known.

Calculate the amount of iron substance that will result in hydrogen interaction with 480g iron oxide (III).

We write down known values \u200b\u200bin the task condition.

Dano: M (Fe2O3) \u003d 4

We also write down that it is necessary to find as a result of solving the problem.

To find : n (Fe) -?

Getting to solve the problem.

Decision: 1). To solve such problems, first need to record the reaction equation described in the task condition.

Fe2O3 + 3 H2HTTPS: //pandia.ru/text/78/038/images/image004_4.png "width \u003d" 12 "height \u003d" 26 src \u003d "\u003e, where N is the amount of substance, m - the mass of this substance, and M is the molar mass of the substance.

Under the condition of the problem, we are not known for the mass of the received iron, i.e., two values \u200b\u200bare unknown in the formula of the amount of substance. Therefore, we will look for the amount of substance in the amount of substance of iron oxide (III). The amounts of substance of iron and iron oxide (III) as follows.

https://pandia.ru/text/78/038/images/image006_4.png "height \u003d" 27 src \u003d "\u003e; where 2 sthechiometric coefficient from the reaction equation facing iron, and 1 is the coefficient facing oxide Iron (III).

hence N (FE) \u003d 2 N (Fe2O3)

3). We find the amount of iron (III) oxide substance.

n (Fe2O3) \u003d https://pandia.ru/text/78/038/images/image008_4.png "width \u003d" 43 "height \u003d" 20 src \u003d "\u003e - molar mass of iron oxide (III), which we calculate Based on the relative atomic masses of iron and oxygen, as well as given the number of these atoms in iron oxide (III): M (Fe2O3) \u003d 2x 56 + 3x 16 \u003d 112 + 48 \u003d 160 aluminum "HREF \u003d" / TEXT / CATEGORY / ALYUMINIJ / " Rel \u003d "Bookmark"\u003e Aluminum?

Write the task condition.

Given: M (AL) \u003d 54g

And also write down that we need to find as a result of solving the problem.

To find : V (h2) -?

Getting to solve the problem.

Decision: 1) Record the response equation by the condition of the problem.

2 Al + 6 HCl https://pandia.ru/text/78/038/images/image011_1.png "width \u003d" 61 "height \u003d" 20 src \u003d "\u003e n - the amount of the substance of this gas.

V (H2) \u003d VM * N (H2)

3). But in this formula, we do not know the amount of hydrogen substance.

four). Find the amount of hydrogen substance in the amount of aluminum substance according to the following ratio.

https://pandia.ru/text/78/038/images/image013_2.png "height \u003d" 27 src \u003d "\u003e; hence n (H2) \u003d 3 n (AL): 2, where 3 and 2 are stoichiometric coefficients , respectively, in front of hydrogen and aluminum.

5) .. PNG "width \u003d" 33 "height \u003d" 31 src \u003d "\u003e

n (Al) \u003d https://pandia.ru/text/78/038/images/image016_1.png "width \u003d" 45 "height \u003d" 20 src \u003d "\u003e * 6 mol \u003d 134, 4 l

We write the answer.

Answer: V (H2) \u003d 134, 4 l

The task of calculating the amount of the amount of the substance (or volume) of the gas required for the reaction with a certain amount of substance (or volume) of another gas.

What amount of oxygen substance will be required to interact with 8 moce of hydrogen under normal conditions?

We write the terms of the task.

Dano: n (h2) \u003d 8mol

As well as write out that it is necessary to find as a result of solving the problem.

To find : n (O2) -?

Getting to solve the problem.

Decision: one). We write the reaction equation by following the condition of the problem.

2 h2 + o2https: //pandia.ru/text/78/038/images/image017_1.png "width \u003d" 32 "height \u003d" 31 src \u003d "\u003e \u003d; where 2 and 1 are stoichiometric coefficients facing hydrogen and oxygen, respectively, in the reaction equation.

3). Hence 2 N (O2) \u003d N (H2)

And the amount of oxygen substance is: n (O2) \u003d N (H2): 2

four). It remains for us to substitute the data from the condition of the problem.

n (o2) \u003d 8mol: 2 \u003d 4 mole

five). We write the answer.

Answer: n (o2) \u003d 4 mole

Instruction

The mass fraction of the substance is by the formula: w \u003d m (B) / m (cm), where W is the mass fraction of the substance, M (B) is the mass of the substance, M (cm) - the mass of the mixture. If dissolved, it looks like this: w \u003d m (B) / m (p-ra), where M (p-ra) is a mass of solution. A mass of the solution, if necessary, can also be found: m (p-ra) \u003d m (c) + m (p-la), where m (Р-la) is the mass of the solvent. If desired, a mass fraction can be multiplied by 100%.

If the problem is not given in the condition of the problem, it can be calculated using several formulas, the data can be used to choose the value in the condition. The first formula for: m \u003d v * p, where m is a mass, V - volume, P is density. The following formula looks like this: m \u003d n * m, where m is a mass, n - the amount of substance, M is the molar mass. The molar mass in turn consists of atomic masses of elements that are part of the substance.

For a better understanding of this material, we will solve the task. The mixture of copper and magnesium sawdust weighing 1.5 g was treated with excess. As a result of the reaction of hydrogen with a volume of 0.56 l (). Calculate the mass fraction of copper in the mixture.
In this problem passes, write its equation. Of two substances with an excess of hydrochloric acid, only magnesium: Mg + 2HCl \u003d MgCl2 + H2. To find a mass fraction of copper in a mixture, it is necessary to substitute the values \u200b\u200bto the following formula: W (Cu) \u003d M (Cu) / M (cm). The mass of the mixture is given, we will find a mass of copper: M (Cu) \u003d M (cm) - M (Mg). We are looking for a lot: M (Mg) \u003d n (Mg) * M (Mg). Find the amount of magnesium substance will help the reaction equation. We find the amount of hydrogen substance: n \u003d v / vm \u003d 0.56 / 22.4 \u003d 0.025 mol. According to the equation, it is clear that n (h2) \u003d n (Mg) \u003d 0.025 mol. We calculate the mass of magnesium, knowing that the molar is 24 g / mol: M (Mg) \u003d 0.025 * 24 \u003d 0.6 g. We will find a mass of copper: M (Cu) \u003d 1.5 - 0.6 \u003d 0.9 g. Calculate a mass fraction: w (Cu) \u003d 0.9 / 1.5 \u003d 0.6 or 60%.

Video on the topic

note

The mass fraction cannot be more than one or if it is expressed as a percentage, more than 100%.

Sources:

• "Handbook of Chemistry", G.P. Homchenko, 2005.
• Calculation of sales share in the region

The mass fraction shows in percent or in the fraction of the content of the substance in any solution or element in the composition of the substance. The ability to calculate a mass fraction is useful not only in chemistry lessons, but also when you want to prepare a solution or a mixture, for example, in culinary purposes. Or change the percentage, in your already existing ones.

Instruction

For example, you need a minimum of 15 cubic meters for the winter. Meters of birch firewood.
Look in the reference density of birch wood. This is: 650 kg / m3.
Calculate the mass, substituting the values \u200b\u200bin the same specific density formula.

m \u003d 650 * 15 \u003d 9750 (kg)

Now, based on the load capacity and capacity of the body, you can decide on the type of vehicle and the number of travel.

Video on the topic

note

A more older people are more familiar with the concept of specific gravity. The specific density of the substance is the same as the proportion.

The mass fraction of the substance shows its content in a more complex structure, for example, in a alloy or mixture. If the total mass of the mixture or alloy is known, then the heavy mass fractions of the components can be found their masses. Find a mass fraction of a substance, you can know its mass and mass of the whole mixture. This value can be expressed in dolleny values \u200b\u200bor percentages.

You will need

• libra;
• periodic table of chemical elements;
• calculator.

Instruction

Determine the mass fraction of the substance that is in the mixture through the mass of the mixture and the substance itself. To do this, with the help of weights, determine the masses constituting the mixture or. Then fold them. Take the resulting mass for 100%. To find a mass fraction of a substance in a mixture, divide it M mass on a mixture M mixture, and the result multiply by 100% (Ω% \u003d (m / m) ∙ 100%). For example, in 140 g of water dissolve 20 g of cook salt. To find a mass fraction of salt, fold the masses of these two substances M \u003d 140 + 20 \u003d 160, then find a mass fraction of the substance Ω% \u003d (20/160) ∙ 100% \u003d 12.5%.

If you want to find a mass fraction of an element in a substance with a well-known formula, use the periodic table of elements. On it, find the atomic masses of the elements that in substances. If one in the formula several times, multiply its atomic mass on this number and fold the results obtained. This will be the molecular weight of the substance. To find a mass fraction of any element in such substance, divide its mass number in this chemical formula M0 on the molecular weight of this substance M. The result Multiply by 100% (Ω% \u003d (m0 / m) ∙ 100%).

For example, determine the mass fraction of chemical elements in copper cune. Copper (copper sulfate), has a Cuso4 chemical formula. Atomic masses of elements included in its composition are equal to Ar (Cu) \u003d 64, Ar (S) \u003d 32, Ar (O) \u003d 16, the mass numbers of these elements will be equal to M0 (Cu) \u003d 64, M0 (S) \u003d 32, M0 (O) \u003d 16 ∙ 4 \u003d 64, taking into account that the molecule contains 4 atoms. Calculate the molecular weight of the substance, it is equal to the sum of the mass numbers of the components of the molecule of substances 64 + 32 + 64 \u003d 160. Determine the mass fraction of copper (Cu) as part of the copper sulfate (Ω% \u003d (64/160) ∙ 100%) \u003d 40%. By the same principle you can determine the mass fractions of all elements in this substance. Mass fraction of sulfur (S) Ω% \u003d (32/160) ∙ 100% \u003d 20%, oxygen (o) Ω% \u003d (64/160) ∙ 100% \u003d 40%. Note that the sum of all mass fractions of the substance should be 100%.

1. What shows the mass fraction of the substance in solution?
Mass fraction - the ratio of the mass of the dissolved substance to the mass of the solution.

2. How can I prepare a solution with a given mass fraction of a dissolved substance? Give an example.

3. What is the difference between the concepts "saturated solution" and "concentrated solution"?

4. In 513 g of distilled water dissolved 27 g of salts. Calculate the mass fraction (as a percentage) of the dissolved substance in the resulting solution.

5. When evaporation, 25 g of the solution was obtained by 0.25 g of salts. Determine the mass fraction of the dissolved substance and express it in percent.

6. 500 g of solution with a mass fraction of sodium hydroxide 0.2 is given. Calculate the mass of the substance that is obtained by evaporation of this solution.

7. By 200 g of solution, a mass fraction of a substance in which is 0.3, 100 g of water was added. Calculate the mass fraction of the dissolved substance in the resulting solution.

8. Calculate a mass of 5.5 liters of sulfuric acid, if the density of such a solution at 20 ° C is 1.06 g / ml.

9. Calculate the density of the solution of hydrochloric acid, if 560 g of such a solution occupies a volume of 500 ml.

Test tasks

1. Indicate the correct statement.
1) a solution containing a multi-solid substance is called concentrated.
2) a solution containing a multi-solid substance is called diluted.
1)

2. In 325 g of water dissolved 25 g of salts. Mass fraction of salt in the resulting solution is equal to
1) 0,71% 2) 7,1% 3) 14,2% 4) 1,42%
2)

3. Install the correspondence between the physical size and formula for its calculation.
1) Mass fraction of the element in the connection
2) mass fraction of substance in solution
3) density

1) -B, 2) -B, 3) -A