###### Equations

Equations P and Q represent two reactions which describe methods of preparing $$CO_2$$

$$P) CH_4+2O_2$$$$CO_2+2H_2O$$

$$Q) CaCO_3$$$$CaO+CO_2$$

Answer 2 (P – combustion; Q – decomposition). Combustion reaction: the products of this reaction are always carbon dioxide and water. Decomposition reaction: any compound breaks into parts.

###### Formulae

The formulae of compounds W, X and Y are shown. These are ions with a positive charge.

W $$FeSO_4*7H_2O$$

X $$Na_2CO_3*10H_2O$$

Y $$BeC_2O_4*H_2O$$

Which statement is correct?

W contains 14 atoms of hydrogen and 11 atoms of oxygen;

X contains 20 atoms of hydrogen and 13 atoms of oxygen;

Y contains 2 atoms of hydrogen and 5 atoms of oxygen.

###### Reactions

Chemical reaction with the release of heat is called:

The reaction is exothermic.

###### Equations

In the scheme of  transformations:  $$SiO_2 (+ X) \to K_2SiO_3 (+ Y) \to BaSiO_3$$, X and Y substances are, respectively

The correct answer is 3 ($$KOH$$$$BaCl_2$$)

$$SiO_2 + 2KOH \to K_2SIO_3 + H_2O$$

$$K_2SIO_3 + BaCl_2 \to BaSiO_3 + 2KCl$$

###### Equations

In the scheme of  transformations:  $$Al_2(SO_4)_3 \to X_1 \to X_2 \to AlCl_3, X_1 and X_2$$ substances are, respectively

The correct answer is 4 ($$Al(OH)_3, A_2O_3$$).

$$Al_2(SO_4)_3 + 6NaOH \to 2Al(OH)_3 + 3Na_2SO_4$$

$$2Al(OH)_3 \to Al_2O_3 + 3H_2O$$

$$Al_2O_3 + 6HCl \to 2AlCl_3 + 3H_2O$$

###### Equations

Which reactions are the reactions of ion exchange?

This reaction is $$KOH + HCl \to KCl + H_2O$$

###### Amount of substance

The greatest amount of sodium ions is formed by dissociation of 1 mole solution of

3 mole of sodium ions are formed by dissociation of 1 mole of sodium phosphate.

$$Na_3PO_4 \leftrightarrow 3Na^+ + PO_4^{3-}$$

###### Amount of substance

The greatest amount of ions is formed by dissociation of 1 mole solution of:

5 mole of ions are formed by dissociation of 1 mole $$Al_2(SO_4)_3$$

$$Al_2(SO_4)_3 \leftrightarrow 2 Al ^{3+} + 3SO_4^{2-}$$

###### Amount of substance

The compound of type $$Na_2MO_4$$ forms each element of two:

The correct answer is $$S, Cr$$

$$Na_2SO_4$$$$Na_2CrO_4$$

###### Amount of substance

Calculate the number of hydrogen molecules which occupy a volume of 5 liters of hydrogen (standard conditions).

The number of molecules: $$N = n* N_A, N_A = 6.02 * 10^{23} mol^{-1}$$

$$n=V/V_m, V_m = 22,4 l*mol^{-1}; n = 5/22,4 = 0,22 mol$$.

$$N = 0,22* 6.02 * 10^{23} = 1,32*10^{23}$$ molecules.

###### Amount of substance

Determine the amount of substance of sulfur oxide (IV), if its volume (standard conditions) was 28 liters. Enter that number in the answer field.

$$V_m = 22,4 l*mol^{-1}$$

$$n(SO_2) = V/V_m = 28/22,4 = 1,25 mol$$

###### Amount of substance

Molecular oxygen takes (standard conditions) volume 7.28 liters. Calculate the mass of gas. Enter that number in the answer field.

$$m(O) = n*A_r, V_m = 22,4 l*mol^{-1}, A_r(O) = 16 g* mol^{-1},$$

$$n=V/V_m = 7,28/22,4 = 0,325 mol,$$

$$m(O) = 0,325* 16 = 5,2 g$$

###### Formulae

The compound composition $$K_2EO_3$$ forms each of the two elements:

The correct answer is 2 ($$N, S$$)

$$K_2NO_3, K_2SO_3$$

###### Formulae

What compounds exhibit the same degree of the oxidation of iron?

The correct answer is 1 ($$Fe^{2+}O, Fe^{2+}CO_3$$

###### Formulae

Among the presented substances: $$CH_4, H_2S, CH_3COOH, NH_3, H_5IO_6, K_2HPO_4$$ acids are:

The correct answer is 2 ($$H_2S, CH_3COOH, H_5IO_6$$)