###### State of matter

True or not the following propositions about pure substances and mixtures?

A. A mixture of salt and sand is heterogeneous.

B. When dissolving salt formed heterogeneous mixture in water.

A mixture of salt and sand is heterogeneous.

###### State of matter

Which of given properties belong to gas?

Properties of gas: occupy the entire amount provided, easily compressed, do not have their own form.

###### State of matter

The molecules are densely packed, are strongly attracted to each other, and each molecule fluctuates around a certain point.

What is this?

This is a solid.

###### Atom

The relative charge on a proton is

The relative charge on a proton is +1.

###### Atom

True or not the following propositions about substances purification techniques and methods of separation of mixtures:

A. Pure water can be cleaned from oil impurities by distillation.

B. The first step in the separation of any mixture of solids is dissolving in the water.

Both propositions are true

###### Atom

True or not the following propositions about methods of water purification?

A. For the purification of water from the impurities of wood chips it is passed through a bed of river sand.

B. From salt impurities water can be purified by filtration.

For the purification of water from the impurities of wood chips it is passed through a bed of river sand.

###### Atomic structure

In which series of chemical elements the radius of the atom decreases?

In serie $$Al-Mg-Na$$the radius of the atom decreases.

###### Atomic structure

Nitrogen and phosphorus atoms have the same

Nitrogen and phosphorus atoms have the same number of electrons in the outer electronic layer

###### Atomic structure

Which chemical element corresponds to the scheme submitted by the electron shells?

The correct answer is 2 period, VIIA group

###### Relative formula masses and molar volumes of gases

Calculate the mass of sodium hydroxide required for the complete neutralization of 245 g of the solution with a mass fraction of 20% sulfuric acid.
Enter the mass in grams.

This reaction is: $$2NaOH + H_2SO_4 \to Na_2SO_4 + H_2O$$

The mass of purifier $$H_2SO_4: m(H_2SO_4) = 245 * 0,2 = 49 g.$$

The amount of substance $$H_2SO_4: n(H_2SO_4) = m/M_r = 49/98 = 0,5 mol$$

The amount of substance $$NaOH: 2:1$$(coefficients in reaction) $$= n:0,5; n (NaOH) = 1mol$$

The mass of $$NaOH: m(NaOH) = n*M_r = 1* 40 = 40 g$$

The correct answer is 40 g.

###### Relative formula masses and molar volumes of gases

What is the mass fraction of nitrogen in the aluminum nitrate?

The relative molecular mass of $$Al(NO_3)_3: M_r = A_r (Al) + 3*(A_r(N) + 3*A_r(O)) = 213 g*mol^{-1}$$

The relative atomic mass of nitrogen is 14.

The mass fraction of nitrogen in the aluminum nitrate: $$(14*3/213)*100 = 19,7 %$$

###### Relative formula masses and molar volumes of gases

Which diagram of allocation of mass fractions of elements corresponds to the quantitative composition of potassium nitrate?

The relative molecular mass of $$KNO_3: M_r = A_r (K) + (A_r(N) + 3*A_r(O) = 101 g*mol^{-1}$$

The relative atomic mass of potassium is 39.

The mass fraction of potassium in the potassium nitrate: $$(39/101)*100 = 38,6 %$$

The relative atomic mass of nitrogen is 14.

The mass fraction of nitrogen in the potassium nitrate: $$(14/101)*100 = 13,9 %$$

The relative atomic mass of oxygen is 16.

The mass fraction of oxygen in the potassium nitrate: $$(16*3/101)*100 = 47,5 %$$

###### Chemical formulae and chemical equations

Which equation corresponds to a decomposition reaction?

The correct answer is 4 ($$2AgI \to 2Ag + I_2$$)

###### Chemical formulae and chemical equations

The reaction of which solutions produces gas?

The correct reaction is $$K_2CO_3 + 2HCl \to 2KCl + CO_2(g) + H_2O$$

###### Chemical formulae and chemical equations

To 150 g of sodium carbonate solution was added a solution of calcium chloride until no more precipitate. the precipitate weight was 12.0 g
Calculate the mass fraction of sodium carbonate in the initial solution.

The reaction: $$Na_2CO_3 + CaCl_2 \to 2NaCl + CaCO_3(s)$$

The amount of substance $$CaCO_3: n(CaCO_3) = m/M_r = 12/100 = 0,12 mol$$

The amount of substance $$Na_2CO_3: n(Na_2CO_3) = 0,12 mol$$

The mass of $$Na_2CO_3: m(Na_2CO_3) = n*M_r = 0,12 * 106 = 12,72 g$$

The mass fraction of $$Na_2CO_3$$ in the initial solution: $$\omega = (12,72/150) * 100 = 8,5 %$$

###### Ionic compounds

Between which elements an ionic bond is formed?

Cl and Na form an ionic bond.

###### Ionic compounds

In which of the presented reactions carbon is reduced?

In reaction $$2CO + O_2 \to 2CO_2$$ carbon is reduced.

###### Ionic compounds

What reaction is redox?

$$CO_2 + Na_2O_2 → Na_2CO_3 + O_2 + Q$$

$$2NH_3 → N_2 + 3H_2 – Q$$

###### Covalent substances

What type of chemical bond is characteristic for substances which formula $$P_4$$?

For substance $$P_4$$ characteristic nonpolar covalent bond

###### Covalent substances

Which of the phosphorus compounds exhibits a minimal oxidation number?

$$Ca_3P_2$$ phosphorus compound has the lowest oxidation number (-3)

###### Covalent substances

The figure below shows a model of the atom that can form a covalent bond with the oxide.

###### Metallic crystals

Which of the following elements has the most pronounced metallic properties?

Metallic properties are increased in the period from right to left and from top to bottom in the group.

###### Metallic crystals

What is the highest degree of oxidation of the elements of the 3rd period? ties are increased in the period from right to left and from top to bottom in the group.

The highest degree of oxidation is equal to the number of the group html> ties are increased in the period from right to left and from top to bottom in the group.

###### Metallic crystals

In which series of chemical elements metallic properties are reinforced? ties are increased in the period from right to left and from top to bottom in the group.

The correct row is $$Li → Na → K$$

###### Electrolysis

What conducts electricity?

Molten sodium sulfate conducts electricity.

###### Electrolysis

Electrolyte is a substance which formula…

Electrolyte is a substance which formula $$HNO_3$$

###### Electrolysis

Which equations correspond to electrolyzed aqueous solution of magnesium chloride?

The correct reactions are:

$$MgCl_2 + 2H_2O → H_2 + Cl_2 + Mg(OH)_2$$

$$2Cl^— — 2e → Cl_2^0$$

$$2H_2O + 2e → H_2^0 + 2OH^—$$