Periodicity of Chemical Properties of the Elements in Period 3 (Cambridge (CIE) AS Chemistry): Exam Questions

Complete Table 2.1 to state the acid-base character of the oxides of the Period 3 elements from sodium to sulfur. Use the terms acidic, basic or amphoteric.

Table 2.1

Some of the oxides react with water.

i) Construct an equation for the reaction of each of these oxides with water.

Na₂O

SO₂

[2]

ii) State the pH of the resulting solution in each case.

Na₂O

SO₂

[1]

State the oxidation number for the Period 3 element in each oxide.

Na₂O

SO₂

The melting points of two Period 3 oxides are shown in Table 2.2.

Table 2.2

Explain the difference in the melting points of Na₂O and SO₂ in terms of their structure and bonding.

The melting points of some Period 3 chlorides are given in Table 4.1.

Table 4.1

*sublimes at 451 K

Construct an equation, with state symbols, for the reaction of phosphorus with chlorine to form phosphorus(V) chloride, PCl₅.

Explain the following in terms of structure and bonding.

i) The high melting point of sodium chloride

[2]

ii) The low melting point of silicon tetrachloride

[2]

Write an equation for the reaction of silicon tetrachloride with water.

Suggest a value for the pH of the solution formed when each of the following compounds is dissolved in water.

NaCl

PCl₅

The ionic radii for the Period 3 elements are given in Table 5.1.

Table 5.1

On Fig. 5.1, sketch a graph to show the variation in ionic radius of the Period 3 elements.

Fig. 5.1

i) On Fig. 5.2, sketch a graph to show the variation in electrical conductivity across Period 3.

Fig. 5.2

[2]

ii) Explain the variation in electrical conductivity of the elements across Period 3.

[3]

Period 3 elements can react with oxygen to form oxides.

Complete the table to give the formula of one oxide of each of these elements.

Aluminium oxide is amphoteric. Explain what is meant by the term amphoteric and include equations for its reactions to illustrate your answer.

Sodium oxide, Na₂O, and sulfur dioxide, SO₂, are added separately to water.

For each oxide, construct an equation for its reaction with water, describe what is observed and state the pH of the resulting solution.

Reaction of Na₂O with water

equation

observation

pH

Reaction of SO₂ with water

equation

observation

pH

Silicon dioxide, SiO₂, is heated with concentrated aqueous sodium hydroxide.

Construct an ionic equation for this reaction.

Compound A is an oxide of a Period 3 element. It dissolves in hot, concentrated potassium hydroxide and in nitric acid, but it is insoluble in water.

i) State the term used to describe this behaviour of compound A.

[1]

ii) Write equations for the reactions of compound A with potassium hydroxide and with nitric acid.

[2]

Explain the variation in the acid-base character of the Period 3 oxides from sodium to sulfur. In your explanation, refer to electronegativity and bonding.

Phosphorus(V) oxide, P₄O₁₀, reacts with water.

i) Construct an equation for this reaction and state the expected pH of the resulting solution.

[2]

ii) Explain why phosphorus(V) oxide has a low melting point.

[2]

Phosphorus(V) oxide reacts with aqueous sodium hydroxide to form a phosphate salt.

i) Construct an equation for this reaction.

[1]

ii) Use oxidation numbers to explain whether or not this reaction is a redox reaction.

[2]

Silicon(IV) chloride, SiCl₄, is formed by the reaction of silicon with chlorine.

i) Construct an equation for this reaction.

[1]

ii) State the shape of a molecule of silicon(IV) chloride.

[1]

iii) Explain why silicon(IV) chloride is a liquid at room temperature.

[2]

Silicon(IV) chloride reacts vigorously with water, whereas tetrachloromethane, CCl₄, does not react with water.

Explain this difference in reactivity.

i) Construct an equation for the reaction of silicon(IV) oxide with hot concentrated aqueous sodium hydroxide.

[1]

ii) Suggest why silicon(IV) oxide does not react with acids.

[1]