You will need

- calculator.

Instruction

1

Any solution consists of a solute and solvent. In most cases the solvent is water. To calculate the percentage

**concentration**(or mass fraction of the solute), you must use the formula:W = m (solute) / m (**solution**) x 100% W – mass fraction of solute (or percent concentration), %From the same formula, we can deduce the mass of solute if you know the mass**of the solution**and percent concentration**of a solution**.2

Example No. 1. Calculate the mass fraction (percentage) of salt (NaCl) if the mass of (NaCl) 5 g, and the mass

**of the solution**(NaCl) 100 g. In this problem, it remains only to substitute in the formula proposed in the condition parameters:W = m (b.-VA) / m (R-RA) x 100 % W (NaCl) = m (NaCl) / m (**solution**NaCl) x 100 % W (NaCl) = 5 g / 100 g x 100 % = 5 %Answer: W (NaCl) = 5 %3

Example No. 2. Calculate the mass percent ( % ) potassium bromide (KBr), if the mass of salt (KBr) 10 g, and the weight of water, 190 g Before using formula to calculate percentage concentration, calculate the mass

**of the solution**, which consists of water and dissolved substances:m (**solution**) = m (solute) + m (water) Consequently:m (R-RA KBr) = 10 grams + 190 grams = 200 godstate in the basic formula are found and specified in the condition parameters:W = m (b.-VA) / m (R-RA) x 100 % W (KBr) = m (KBr) / m (**solution**KBr) x 100 % W (KBr) = 10 g / 200 g x 100 % = 5% Answer: W (KBr) = 5 %4

Example No. 3. Calculate the percentage

**concentration**of acetic acid (CH3COOH), if the mass of the acid (CH3COOH) and 30 g, and the mass of water 170 g. Calculate the mass**of the solution**, which consists of water and acetic acid:m (**solution**) = m (solute) + m (water) Consequently:m (R-RA CH3COOH) = 30 g + 170 g = 200 godstate in the formula of required parameters:W = m (b.-VA) / m (R-RA) x 100 %W (CH3COOH) = m (CH3COOH) / m (**solution**CH3COOH) x 100 % W (CH3COOH) = 30 g / 200 g x 100 % = 15% Answer: W (CH3COOH) = 15 %# Advice 2 : How to calculate the concentration of the solution

Concentration - the quantity that determines the number present in the solution of the substance. Most commonly used in a chemistry experiment, it is important that the solution was prepared correctly), sometimes it finds application in other Sciences, and sometimes in everyday life (to prepare the most accurate solution of salt, sugar, soda, etc.).

You will need

- A textbook in analytical or General chemistry any author.

Instruction

1

It should be noted that the composition of the solution (or concentration of dissolved substances in the solution) is expressed in different ways: dimensional and dimensionless quantities. Dimensionless quantities (fractions, percentages) to the concentrations are not relevant, because the concentration - the value dimension. In chemistry mainly use 3 types of concentrations: molar concentration or molarity, molalla concentration or the molality and the equivalent normal concentration.

The molar concentration or molarity is the ratio of the amount of a substance to the volume of the solution. The formula is Cm = n/V where n is amount of substance, mol V is the volume of solution, l is Also the concentration can be denoted by the letter M after the number. So, for example, 5 M HCl means that Cm(HCl) = 5 mol/l, i.e. 5 mol HCl are in 1 liter of water. Note: if the task is not specified quantity of the substance, but given his weight, we can use the formula n = m/Mr where m is the mass of the substance, g, Mr - molecular weight (calculate using table D. I. Mendeleeva), n - amount of substance, mol. This concentration varies with the increase or decrease of temperature.

The molar concentration or molarity is the ratio of the amount of a substance to the volume of the solution. The formula is Cm = n/V where n is amount of substance, mol V is the volume of solution, l is Also the concentration can be denoted by the letter M after the number. So, for example, 5 M HCl means that Cm(HCl) = 5 mol/l, i.e. 5 mol HCl are in 1 liter of water. Note: if the task is not specified quantity of the substance, but given his weight, we can use the formula n = m/Mr where m is the mass of the substance, g, Mr - molecular weight (calculate using table D. I. Mendeleeva), n - amount of substance, mol. This concentration varies with the increase or decrease of temperature.

2

Molalla concentration or molality - the ratio of the amount of a substance to the mass of the solvent. Calculated by the formula m = n/ M (solution), where n - amount of substance, mol, M (solution) - mass of solution, kg. m(HCl)= 5 mol/kg (H2O) means that 1 kg of water corresponds to 5 mol of HCl. A solvent is not necessarily water (it depends on the conditions of the task), amount of substance can be calculated (method specified in the first paragraph), at a temperature of molalla concentration does not change.

3

Equivalent or normal concentration - the ratio of the number of equivalents of solute to volume of solution. Denote the normal concentration can be CH or the letter n after the number. For example, 3 n Hcl - means solution, per liter which is 3 equivalent of hydrochloric acid. The calculation of the equivalent - is a separate issue, which if necessary can be found in a school textbook in chemistry. This concentration is often used in analytical chemistry when you need to find out which volume ratios to mix solutions: the solute should have no residue to react, i.e. C1*V1 = C2*V2 where C1 and V1 are concentration and volume of one solution and C2 and V2 are the concentration and volume of another solution. Using these types of concentrations, it is possible to solve the problem.

# Advice 3 : How to calculate the concentration of a substance

The concentration of the solution is a measure of how much mass or other

**substances**contained in a certain volume or mass of solution. Even the most remote from chemistry, one is faced with this concept at every step: for example, buying in the store 9% vinegar for home canning, or 20% cream to add to coffee. How is calculated the concentration of the solution?Instruction

1

Suppose 200 or 300 milliliters of water dissolve 58.5 grams of sodium chloride, that is familiar to all of salt. Then, Prilepa water brought the total weight of the solution up to one kilogram. It is easy to guess that the solution in this case will contain 58.5 grams of salt and 941,5 grams of water. What will be the mass fraction of salt?

2

To calculate it is easy, for this amount of salt, divide by the total mass of solution and multiply by 100%, it will look like the following:(58,5/1000) * 100% = 5,85%.

3

Formulate the task a little differently. The same amount of salt dissolved in water, then brought the solution volume up to one liter. What will be the molar concentration of the solution?

4

Remember the definition of molar concentration. This is the number of moles of dissolved

**substance**contained in one liter of solution. What is the mol of salt? Its formula is NaCl, the molar mass is approximately 58.5 per. In other words, in one liter of solution you have contains exactly one mole of salt. You will receive a 1.0 molar solution.5

Now go back to the original conditions of the problem where the total weight of the solution amounted to exactly one kilogram. How do you find the molality of this solution?

6

And here, too, there is nothing difficult. Above you have already figured out that 58.5 grams of common salt have 941, 5 grams of water. Substituting the known values into the formula m = v/M, where M is the value of the molality and v is the number of moles

**of the substance**in the solution, and M is the mass of solvent in kilograms, we get:1,0/0,9415 = 1,062 Moralny solution.Useful advice

The concentration can be expressed in many different ways. For example, using the concepts of "mass fraction", "molarity" (i.e., how many moles of a substance is in 1 liter solution), molality (number of moles of a substance is in 1 kilogram of solvent), etc.

# Advice 4 : How to calculate the initial concentration

In the course of a reaction some substances are transformed into others while changing its composition. Thus, the "source

**concentration**"is**the concentration of**substances prior to the occurrence of a chemical reaction, that is, converting them into other substances. Of course, this transformation is accompanied by a decrease in their number. Accordingly, it reduced the**concentration**of the starting materials, until a zero value if the reaction has proceeded to the end, irreversibly, and the components were taken in equal amounts.Instruction

1

Say you have the following task. Was leaking some kind of chemical reaction in which a starting material taken as A and B, turned into products, for example, relatively To and G. That is, the reaction took place according to the following scheme: A + B = B + G. If the concentration of substance B is equal to 0.05 mol/l, and the substance G to 0.02 mol/l, was established a kind of chemical equilibrium. You need to determine what the initial concentrations A0 and B0, if the equilibrium constant Kr is equal to the amount of 0.04?

2

To solve this problem take the equilibrium concentration of the substance And the value of "x" and the concentration of a substance In for "y". And also remember that the equilibrium constant Kr is calculated by the following formula: [V][G]/[A][B].

3

In the course of solving we get the following calculation: 0,04 = 0,02 y /x of 0.05. That is, by simple calculation you will get that y = 0.1 x.

4

Now once again look closely at the above chemical equation. From this it follows that one mole of the substances A and B were formed on one pray compounds In G. Based on this, the initial molar concentration of a can be represented as follows:A0 = x + 0,02 A0 = x + y

5

Remember that the value of "y" as you just defined, is equal to one level of 0.1 x. Transforming these equations in the future, you will get: x + 0,02 = 1.1 x. From this it follows that x = 0.2 mol/l, and then the initial concentration [A0] is equal to 0,2 + 0,02 = 0.22 mol/l.

6

What substance B? The initial concentration B0 is much easier. To determine the equilibrium

**concentration**of the substance necessary to allow the equilibrium concentration of the product-substance of G. That is, [B0] = 0,05 + 0,02 = 0,07 mol/l. the Answer will be: [A0] = 0.22 mol/l, [B0] = 0,07 mol/l. the task is solved.# Advice 5 : How to find the percentage concentration

Concentration is the value which characterizes the qualitative composition of the solution. Concentration is called the number of the solute or its mass to the total volume or mass of fluid. Thus, the most important characteristics are the mass and volume fraction.

You will need

- - the mass of the solute;
- - the mass of the solution.

Instruction

1

Mass fraction, it is the same percentage concentration is a dimensionless quantity, which is equal to the ratio of the mass solute to the total weight of the liquid. Most often it is expressed as a percentage, which you multiply the resulting ratio by one hundred. Formula percentage

**concentration**can be recorded in the following way: ω = m in-VA/m R-RA*100%. The first value is the mass of the substance, and the second mass of the solution as a whole.2

Often in the task given percentage concentration of a substance, based on which you want to find the mass of substance / mass of solution. It is very simple, just need to convert the original formula. To find the mass of a substance it will be as follows: m VA = m R-RA* ω/100. The mass of the solution can be found as follows: divide the mass of the substance in percent

**concentration**and then multiply the result by one hundred. The unit mass of a substance and the mass of solution – grams.3

To find the percentage concentration if the solution was obtained with the use of hydrated, you should use a different solution algorithm. The crystalline has the structure of IU(x)-TA(y)*nH2O. In the problem statement, which appears as a crystalline, should contain information about the mass of the hydrated and the dry mass metal-x-acid-y. In this case, the percentage concentration will be equal to the mass of the solution multiplied by the molar mass of hydrated divided by mass of crystalline, multiplied with the ratio dry substance and the molar mass of the anhydrous substance.

Useful advice

Counting the weight of the solution, note that it consists of two quantities: the mass of solvent and mass of a substance dissolved in it. The omission of this fact is a large number of errors during these tasks.

# Advice 6 : 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.

# Advice 7 : How to calculate mass percent

Mass

**percent**is the ratio of the mass of any component of the solution, alloy or mixture to the total weight of the substances in this solution, expressed in**percentage**Ah. The higher**the percentage**, the more the content of a component.Instruction

1

Remember the task set before the great scientist Archimedes king Hieronim, and slightly modify it. Suppose Archimedes found that the roguish goldsmith had stolen some of the gold, replacing it with silver. As a result, the alloy from which were made the Royal crown, consisted of 150 cubic centimeters of gold and 100 cubic centimeters of silver. Task: find the mass

**percentage**of gold in the alloy.2

Remember the density of these precious metals. 1 cubic cm of gold contains 19.6 grams of 1 cubic cm of silver is 10.5 grams. To simplify, you can round these values to 20 and 10 grams, respectively.

3

Next, perform the calculation: 150*20 + 100*10 = 4000 gram, that is 4 pounds. This is the alloy used for fabrication of the crown. Since the problem says nothing about the "waste" will get the response: 150*20/4000 = 3/4 = 0,75. Or in another way, 75%. That was the mass

**percentage**of gold in a supposedly "pure gold" the crown of Hiero.4

And if you were dealing with a solution? For example, you have been given this task: to determine the mass

**percentage**of salt (sodium chloride) in it dvuhosnom solution.5

And there is absolutely nothing complicated. Remember, what is the molarity. This is the number of moles of substance in 1 liter of solution. Mol, respectively, the amount of a substance whose mass (in grams) equal to its mass in atomic units. You have only to write the formula of common salt, and learn a lot of its components (in atomic units), looking at the periodic Table. The mass of sodium is 23.e.m. the mass of chlorine is 35.5.e.m. The amount you get of 58.5 grams/mol. Accordingly, the mass of 2 moles of salt = 117 grams.

6

Therefore, in 1 liter of 2M aqueous solution of sodium chloride contains 117 grams of the salt. What is the density of this solution? According to the table of densities, find that it is approximately equal to 1.08 g/ml. Therefore, in 1 liter of this solution will contain about 1080 grams.

7

And then the problem is solved in one step. By dividing the mass of salt (117 grams) the total weight of the solution (1080 g), we get: 117/1080 = 0,108. Or in

**the percentage of**Oh is 10.8%. This is the mass**percentage**of salt in its 2M solution.Note

Mass percentage of sodium chloride will remain unchanged, regardless of the number of the solution.

Useful advice

When solving the problem with the gold alloy you used the rounded value of the density of gold and silver. If you want more precision, this is unacceptable.

# Advice 8 : How to calculate the concentration

With the concept of the concentration of people is found not only in science but also in everyday life. For example, the mass fraction of fat listed on food products (milk, butter etc.) are not that other, as percentage concentration. Also it has another molar, normal and molalla concentration. And any of them easily calculated.

You will need

- - handle;
- paper;
- - the periodic table;
- calculator.

Instruction

1

To find the mass fraction (percentage

**concentration**) of a substance, divide its mass by the total mass of the solution (mixture). The result will be in fractions of a unit, which can then convert into a percentage that will also be true. For example, given the task: to prepare the solution took 150 g of water and 50 g sugar. You must calculate the percentage**concentration**of the solute. For the solution first, write the formula and then find the optimum value:ω (sugar)= m(sugar)/m(solution) = 50/ (150+50) =0,25 * 100% = 25%the solution contains 25% sugar.2

When calculating the molar concentration, you need the amount of substance divided by the total volume of the solution. The unit of measure in this case would be mol/L. the Formula for calculation is as follows: C = n(solute)/V, where C is the molar concentration (mol/l);n – amount of substance (mol);V is the total volume of the mixture (liter).

3

Normal concentration is expressed in gram equivalent/liter and represents the number of equivalents of a certain substance in 1 l of solution, which is, in chemical reactions, 1G of hydrogen or 8 g of oxygen. Suppose you want to calculate the normality of 70% sulfuric acid, the density of which is equal to 1,615 g/l. the conditions of the problem it is clear that 100 g of solution contains 70 grams of acid. So first find the volume of a given solution: V = 100/1,615 = accounting period 61.92 (ml). Then calculate the mass of H2SO4 in 1 liter of solution: m(H2SO4) = 1000*70/61,92 = 1130,49 (g). And then calculate the normality, considering that the acid is dibasic:SN = m*z/ M =1130,49*2/98 = N of 23.06.

4

If you want to calculate molalou

**the concentration**of the solution (molality), use the following formula: Cm = n/m, gdes – molalla concentration is measured in mol/kg;n – number of a certain substance in moles;m is the total mass of the solution in kilograms.Unlike molarity molalla concentration depends on the temperature conditions of the reaction.Useful advice

In analytical chemistry are often used instead of concentration titer. It shows the amount of a certain substance in each milliliter of solution.

# Advice 9 : How to find the concentration of acid

The concentration of the

**acid**– value that indicates what proportion of this substance is a certain quantity or volume of its solution. It can be expressed in different ways: in the form of a mass fraction, molarity, molality, etc. In laboratory practice, it is often necessary to determine**the concentration of****acid**.You will need

- - graduated measuring Cup;
- - laboratory scales;
- - glass pipette;
- - litmus;
- the alkali solution.

Instruction

1

Suppose you have a container label H2SO4. That is, once it becomes clear that it contains sulfuric acid. But no more information there. How do you determine its

**concentration**? You can do this by using the table of densities of solutions. There are many directories where the values of the density of the solution of chemicals depending on their concentration.2

Take a graduated measuring Cup, weigh it on a laboratory scale. Denote the mass of the empty Cup as m1. Using a glass pipette add it some volume V of sulfuric

**acid**. Again weigh the Cup, indicate its mass as m2. The density of the**acid**is given by: (m2 – m1)/V.3

According to the table of densities, set

**the concentration**of the solution. Assume that during the described experience, you calculated the density of sulfuric**acid**: 1,303 grams/milliliter. It corresponds to 40% concentration.4

As determined by the concentration of the

**acid**? There are sensitive and very accurate method called direct titration. It is based on the neutralization**of the acid**by the alkali solution whose concentration is known. For example, in the case of sulfuric acid: H2SO4 + 2NaOH = Na2SO4 + 2H2O.5

The reaction scheme shows that to neutralize one mole

**of acid**will need two moles of sodium hydroxide. On this basis, knowing the volume of the investigated solution**of acid**volume of alkali used for its neutralization and**the concentration of the**alkali, we can calculate**the concentration of****acid**.6

But how to determine the exact amount of alkali needed to neutralize the

**acid**? With the indicator changing color. For example, litmus. The experience is so. Over a vessel with known volume of**acid**(which also add a few drops of indicator), attach a graduated burette with the alkali solution.7

Record the reading of the upper level of alkali, then carefully loosening the tap of the burette, drop by drop start to add it to the acid. Your task is to turn off the tap in the moment when the red indicator will disappear. Record the reported lower level of alkali and calculate what its volume left for the neutralization of the

**acid**.8

And then, knowing the magnitude of the volume and the precise

**concentration**of lye is easy to calculate how many moles of alkali are reacted. Accordingly, the number of moles of**acid**was 2 times less. Knowing the initial volume of the**acid**, you will find its molar**concentration**.