Task 435.
How many milliliters of concentrated hydrochloric acid (p \u003d 1.19 g / ml) containing 38% (wt.) National Assembly, you need to take 1 l 2N. Solution?
Decision:
M (nsi) \u003d m e (nsi) \u003d 36.5 g / mol.
Calculate the mass of NSI in 1 l 2n of its solution: 2 . 36.5 \u003d 72.99.
We calculate the mass of the 38% solution by the formula:

where

The volume of the solution that must be taken to prepare 1 l 2N solution calculation by the formula:

m (P-PA) \u003d p. . V,

where p.

Answer: 161.28 ml.

Task 436.
To 100 ml of 96% (by weight) H 2 SO 4 (density of 1.84 g / ml) added 400 ml of water. It turned out a solution with a density of 1.220 g / ml. Calculate its equivalent concentration and mass fraction of H 2 SO 4.
Decision:
Mass of a solution of 100 ml of 96% solution will find by the formula:

m (P-PA) \u003d P . V,

where p. - density, and v - the volume of the solution, we get:

m (P-PA) \u003d 1.84 . 100 \u003d 184

The mass of sulfuric acid in this solution is found by the formula:

where
- mass fraction dissolved substance; m (V-BA) - mass of dissolved substance; M (p-ra) - mass of solution.

We calculate the mass of the solution obtained at a mixture of 100 ml of 96% solution with 400 ml of water, we obtain:

m "(P-PA) \u003d (100 + 400) . 1,220 \u003d 610

We define the molar weight of the equivalent H2SO) 4 of the ratio:

M e (c) - the molar mass of the equivalent of acid, g / mol; M (c) - a molar mass of acid; Z (b) - equivalent number; Z (acids) is equal to the number of ions H +, H 2 SO 4 (((((2.

Then the equivalent concentration of the solution will find by the formula:

where
m (b) is a mass of dissolved substance, M e (B) - the molar mass of the equivalent of a dissolved substance, V - the volume of the solution (in L or ml).

Calculate the mass fraction of the resulting solution:

Answer: 7,2n; 28.96%.

m (P-PA) \u003d P . V,

where p. - density, and v - the volume of the solution, we get:

m (P-PA) \u003d 1.18 . 1000 \u003d 1180

Calculate the mass of hydrochloric acid in the solution by the formula:

where
- mass fraction of a dissolved substance; m (V-BA) - mass of dissolved substance; M (p-ra) - mass of solution.

We define the molar weight of the equivalent of HCl from the ratio:

M e (c) - the molar mass of the equivalent of acid, g / mol; M (c) - a molar mass of acid; Z (b) - equivalent number; Z (acid) is equal to the number of ions H +, H 2 SO 4 → 2.

Answer: 11.8H

Task 438.
What volume is 10% (by weight) of sulfuric acid ( p. \u003d 1.07 g / ml) will be required to neutralize a solution containing 16.0 g of NaOH?
Decision:
The neutralization reaction equation NaOH solution H 2 SO 4 solution has the form:

H 2 SO 4 + 2NAOH ↔ Na 2 SO4 + 2H 2 O

From the reaction equation it follows that the neutralization of 1 mol NaOH is spent 0.5 moles NaOH, it means that the equivalent mass of sulfuric acid in this reaction is 49 g / mol (m / 2 \u003d 98/2 \u003d 49).

Now we calculate the mass of sulfuric acid necessary for neutralization of 16 g NaOH from the proportion:

Mass of a solution containing 19.6 g of H 2 SO 4, calculate the formula:

where
- mass fraction of a dissolved substance; m (V-BA) - mass of dissolved substance; M (p-ra) - mass of solution.

The volume of the solution is calculated by the formula:

m (P-PA) \u003d P . V,

where - density, and V - the volume of the solution, we get:

Answer: 183.18 ml.

The mass fraction of the element ω (e)% is the ratio of the mass of this element M (e) in a taking molecule of the substance to the molecular weight of this substance Mr (V-BA).

The mass fraction of the element is expressed in fractions of one or in percent:

ω (e) \u003d m (e) / mr (V-BA) (1)

Ω% (e) \u003d m (e) · 100% / mr (in-BA)

The sum of the mass fractions of all elements of the substance is 1 or 100%.

As a rule, for calculating the mass fraction of the element, a portion of a substance equal to the molar mass of the substance is taken, then the mass of this element in this portion is equal to its molar mass multiplied by the number of atoms of this element in the molecule.

So, for substance A x in Y in fractions from one:

Ω (a) \u003d Ar (e) · x / mr (V-BA) (2)

From the proportion (2), we derive the calculated formula to determine indexes (x, y) in chemical formula Substances, if the mass shares of both elements and the molar mass of the substance are known:

X \u003d Ω% (A) · Mr (V-BA) / AR (E) · 100% (3)

Dividing Ω% (A) on Ω% (B), i.e. By converting formula (2), we get:

ω (a) / ω (c) \u003d x · ar (a) / y · ar (c) (4)

The calculated formula (4) can be converted as follows:

X: y \u003d ω% (a) / ar (a): ω% (B) / AR (B) \u003d x (a): y (B) (5)

The calculated formulas (3) and (5) are used to determine the formula of the substance.

If the number of atoms in the molecule of the substance for one of the elements and its mass fraction can be determined by the molar mass of the substance:

Mr (V-BA) \u003d Ar (e) · x / w (a)

Examples of solving problems for calculating mass fractions of chemical elements in complex substance

Calculation of mass fractions chemical elements In a complex substance

Example 1. Determine the mass fractions of chemical elements in sulfuric acid H 2 SO 4 and express them as a percentage.

Decision

1. Calculate relative molecular weight Sulfuric acid:

Mr (H 2 SO 4) \u003d 1 · 2 + 32 + 16 · 4 \u003d 98

2. Calculate the mass fractions of the elements.

To do this, the numerical value of the mass of the element (taking into account the index) is divided into a molar mass of the substance:

Given this and denoting the mass fraction of the element of the letter Ω, the calculation of mass fractions is carried out like this:

ω (H) \u003d 2: 98 \u003d 0.0204, or 2.04%;

ω (s) \u003d 32: 98 \u003d 0.3265, or 32.65%;

Ω (O) \u003d 64: 98 \u003d 0.6531, or 65.31%

Example 2. Determine the mass fractions of chemical elements in Al 2 O 3 alumina and express them as a percentage.

Decision

1. Calculate the relative molecular weight of aluminum oxide:

Mr (Al 2 O 3) \u003d 27 · 2 + 16 · 3 \u003d 102

2. Calculate the mass fractions of the elements:

ω (AL) \u003d 54: 102 \u003d 0.53 \u003d 53%

ω (O) \u003d 48: 102 \u003d 0.47 \u003d 47%

How to calculate the mass fraction of the substance in the crystal hydrate

The mass fraction of the substance is the ratio of the mass of this substance in the system by the mass of the entire system, i.e. ω (x) \u003d m (x) / m,

where ω (x) is the mass fraction of the substance X,

m (X) - Mass of the substance X,

m - the mass of the entire system

Mass fraction is a dimensionless value. It is expressed in fractions from one or percentage.

Example 1. Determine the mass fraction of crystallization water in barium chloride dihydrate BACL 2 · 2H 2 O.

Decision

Molar mass BACL 2 · 2H 2 O is:

M (BACL 2 · 2H 2 O) \u003d 137+ 2 · 35.5 + 2 · 18 \u003d 244 g / mol

From the BACL 2 · 2H 2H formula, it follows that 1 mol of barium chloride dihydrate contains 2 mol H 2 O. From here, you can determine the mass of water contained in BACL 2 · 2H 2 O:

m (H2O) \u003d 2 · 18 \u003d 36

We find a mass fraction of crystallization water in barium chloride dihydrate BACL 2 · 2H 2 O.

ω (H 2 O) \u003d M (H 2 O) / M (BACL 2 · 2H 2 O) \u003d 36/244 \u003d 0.1475 \u003d 14.75%.

Example 2. From the sample rock breed Weighing 25 g containing a mineral AG 2 S Mineral is highlighted by silver weighing 5.4 g. Determine the mass proportion of argentita in the sample.

A) Magnesium burning Cool ice melting C) River sand sedimentation in water
D) mixing powders of sulfur and iron E) boiling water

2. The molar weight of the iron is equal
A) 26 g / mol Cool 56 g / mol c) 52 g / mol d) 112 g / mol e) 56

3. In the 2NA2S formula, the number of sodium and sulfur atoms are equal
A) 1 and 2 Cool 4 and 1 c) 2 and 4 d) 4 and 2 E) 2 and 1

4. MN (VII) oxide formula
1. MnO2 Cool Mn2O7 C) Mn2O3 D) MNO3 E) MNO

5. In the P + O2 reaction scheme? P2O5 you need to put coefficients
A) 4, 5, 2 cool 2, 1, 1 c) 2, 5, 2 d 5, 4, 2 e) 2, 4, 5

6. The substitution reaction equation is -
A) 4NA + O2 \u003d 2 Na2O Cool Caco3 \u003d Cao + CO2? C) zn + cus \u003d zns + cu
D) 2mg + O2 \u003d 2MGO E) 2H2 + O2\u003e 2 H2O

7. The iron nail is immersed in a solution of copper (II) chloride (II) is covered with a red copper chain. This is an example of a reaction:
A) Cool exchange decomposition c) substitution d) compound E) non-reaction

8. Symbol of the chemical element of manganese
A)? E Cool MG C) O D) MN E) MR

9. About the chemical element, and not about a simple substance of nitrogen in terms of expression
A) Nitrogen is part of Air COOL into nitric acid HNO3 enters nitrogen
C) nitrogen formula N2 D) liquid nitrogen is sometimes used for freezing products
E) nitrogen inert gas
10. Aluminum is not typical of physical property.
A) Cool conductor Cool thermal conductivity C) Silver-white color
D) ability to magnify e) gas under normal conditions

11. Sign of a sign that allows you to call the rust of the nail chemical reaction - this is:
A) heat release Cool gas allocation c) color change
D) odor appearance e) precipitation

12. Iron sulphide is a complex substance, and not a mixture because
A) It can be divided by a magnet to iron and sulfur
Cool it can be divided by distillation to iron and sulfur
C) consists of atoms of a different chemical element and it cannot be divided physical methods on iron and sulfur
D) it is insoluble in water E) gas under normal conditions

13. 3.01 * 10 23 iron atoms make up
A) 2 mole Cool 3 mol c) 1 mol d) 0.5 mol e) 1.5 mol

14. 69 g sodium constitute
A) 3 mole Cool 1 mol c) 6.3 mol d) 1.5 mol e) 0.5 mol

15. Filtering can be divided mixture:
A) Copper and iron chips Cool sugar and water C) chalk and water
D) water and acetic acid E) water and gasoline

16. The interaction of magnesium with oxygen refers to reactions:
A) decomposition Cool exchange C) compound d) of substitution e) non-reaction

17. K. chemical phenomena relate:
A) grinding marble Cool evaporation of water C) melting ice d) melting copper E) coal combustion

19. What is the valence of aluminum?
A) 1 Cool 2 C) 3 d) 4 E) 5

20. Digital Measuring Molar Mass:
A) grams of Cool gram / mol c) mol d) petograms E) no unit units

21. NaHCO3 molar mass is equal to:
A) 156 Cool 156 g / mol c) 84 g / mol d) 84 e) 84 l

22. For the decomposition reaction:
A) 2H2 + O2\u003e 2 H2O COOL 2NA + 2H2O\u003e 2NAOH + H2
C) C + O2\u003e CO2 D) 2NH3\u003e N2 + 3H2
E) AGNO3 + HCL\u003e AGCL + HNO3

23. Mass fraction of oxygen in sulfuric acid H2SO4 is approximately:
A) 16% Cool 33% c) 65% d) 2% E) 17%

25. In which of these rows is only metals?
A) K, Zn, Fe Cool Si, Ca, Bi C) Al, C, CR D) W, OS, in E) P, AU, PB

26. The mass fraction of sulfur in the substance SO2 is equal to:
A) 32% Cool 64% C) 50% d) 80% E) 12%

27. The zinc sulfide mass formed when heated 10 g of sulfur with zinc is equal to:
A) 12 g Cool 30.31 g c) 25.6 g D) 10.5 g E) 32.4 g

28. Crypton chemical element symbol
A) Ca Cool kr c) k d) CD E) C

29. The substance is
A) air b) copper c) mirror D) granite E) milk

30. In the list of physical properties is too much
A) Cool density burning C) thermal conductivity
D) boiling point E) melting point