Properties of Period 3 Elements & their Oxides (AQA A Level Chemistry)

Period 3 elements all form oxides when they are reacted with oxygen.

Give an equation and two observations when magnesium is heated in oxygen.

Sulfur is another Period 3 element which will burn in air.  Give an equation and two observations for this reaction. 

The melting points of the highest oxides of some of the elements in Period 3 are given in Table 1. 

Table 1

i) Explain the decrease in melting point from phosphorus (v) oxide to sulfur trioxide.

ii) Explain why magnesium oxide has a higher melting point than sodium oxide.

Explain why magnesium oxide forms a weakly alkaline solution when it reacts with water.

The oxides of Period 3 elements magnesium and phosphorus have different melting points. 

Explain this difference, using your knowledge of the structure and bonding of these oxides.

Consider the following oxides.

Na₂O               MgO                P₄O₁₀                SO₂

State which of the oxides will form a solution with the lowest pH and which will form a solution with the highest pH.

The Period 3 oxides will also react with different acids and alkalis.

Give a balanced symbol equation for the following reactions:

i) MgO and HCl

ii) Na₂O and H₂SO₄

iii) SO₃ and KOH

A pharmaceutical company has a waste tank of phosphoric acid (H₃PO₄) with a total volume of 50 000 dm³.  The phosphoric acid was formed by adding phosphorus (V) oxide (P₄O₁₀) to water. 

A 25.0 cm³ sample of this solution required 22.1 cm³ of 2 mol dm^-3 sodium hydroxide solution for complete reaction. 

Calculate the mass, in g, of phosphorus (V) oxide that must have been added to the water in the waste tank.

Aluminium forms an amphoteric oxide with an ionic lattice structure.

i) State the meaning of the term amphoteric.

ii) Give an ionic equation to show the oxide reacting with an acid.

iii) Give a balanced equation to show the oxide reacting with potassium hydroxide.

Silicon dioxide is a white powder which forms when finely divided silicon reacts with oxygen.  It has a melting point of 1883 K and if added to water, the resulting mixture has a pH of 7. However, it is described as an acidic oxide.

i) Describe the shape and bonding of silicon dioxide.

ii) Explain in terms of structure and bonding why it has a high melting point.

iii) Give an equation to represent the reaction between silicon dioxide and hot, concentrated sodium hydroxide.

Sodium oxide melts at 1548 K whereas sulfur dioxide melts at 200 K.

State the structures of each oxide and explain the difference in their melting points.

If sodium oxide and sulfur dioxide are dissolved in separate samples of water, they form solutions with different pH values. 

State the pH values and explain why they are produced.

Sulfur dioxide reacts with water producing sulfuric (IV) acid, whereas sulfur trioxide reacts with water producing sulfuric (VI) acid.

Give an equation for each of these reactions.

The structures of two oxyacids of elements in Period 3 are shown in Figure 1 below.

Figure 1

i) Give the oxidation state of each Period 3 element in both Acid A and Acid B in Figure 1.

ii) Give an equation for the formation of Acid B from an oxide of an element in Period 3.

iii) Give the formula, including the charge, of the two anions formed from Acid A and name these anions.

Phosphorus (V) oxide dissolves in water to form a solution of phosphoric (V) acid.

i) Calculate the mass in grams, of phosphorus (V) oxide required to react with 250 cm³ of water to form a solution of phosphoric (V) acid with a concentration of 0.15 mol dm^-3.

ii) Give an equation for the reaction of phosphorus (V) oxide with magnesium oxide.

Using only the elements from Period 3 answer the following questions.

i) Name an element which forms an oxide in which it has an oxidation state of +6.

ii) Name an oxide with a macromolecular or giant covalent structure and explain why it has a high melting point.

iii) Name an element which burns with a yellow flame in oxygen. Give an equation for this reaction. 

Period 3 oxides all have different structure and bonding types.

i) State the structures of phosphorus (V) oxide and aluminium oxide.

ii) The melting points of phosphorus (V) oxide and aluminium oxide are 300 C and 2072 C respectively. Explain the difference.

Name and draw the shape of the two anions which can be formed from sulfuric (IV) acid.

State the type of bonding in sodium oxide.

Describe a method that a student could use to prove that sodium oxide has this type of bonding.

Figure 1 below shows the displayed formula of sulfuric (VI) acid.

Figure 1

i) Name the shape the sulfuric (VI) acid molecule takes and give a value for its bond angle.

ii) Give an equation to represent the reaction between sulfuric (VI) acid and sodium hydroxide.

Sketch a graph on Figure 1 to show the melting points of the Period 3 oxides.

Figure 1

Explain the difference between the melting point of magnesium oxide, MgO, and aluminium oxide, Al₂O₃.

Sodium oxide, sulfur dioxide and sulfur trioxide are Period 3 oxides.

i) State the type of bonding that exists in sodium oxide, sulfur dioxide and sulfur trioxide.

ii) Explain why sulfur dioxide and sulfur trioxide have different boiling points.

Write an equation to show how phosphorus oxide, P₄O₁₀, reacts with the strong base sodium hydroxide, NaOH. Include state symbols in your equation. 

Sodium oxide and sulfur dioxide are separately added to water. Write equations for and observations of each reaction and state the pH of any solution formed.

A concentrated solution of the compound produced when sodium oxide is added to water is heated with silicon dioxide. Write the 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 that is used to describe the behaviour of the compound A.

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

2.75 g of magnesium oxide was reacted in the lab with 0.50 mol dm^-3 phosphoric acid to produce a compound which can be used as a health supplement for magnesium deficiency and to maintain bone health. 5.56 g of useful product was produced.

Assuming 100% yield, calculate the percentage purity of the magnesium oxide and give your answer to a suitable number of decimal places.

Explain the difference between the structure and the pH of sodium oxide and phosphorus (V) oxide.

The metallic oxides in Period 3 can react with some of the non-metal oxides in the same Period. 

i) Write an equation for the reaction between sodium oxide and phosphorus (V) oxide.

ii) Write an equation for the reaction between magnesium oxide and phosphorus (V) oxide.

Explain the pH values of sodium oxide and magnesium oxide when reacted with water.

Aluminium oxide is another metallic oxide of the Period 3 elements. Write an equation to show how this metallic oxide reacts in a different way to that of sodium oxide and magnesium oxide.

Period 3 oxides can be produced in industry through combustion of fossil fuels, as well as in the blast furnace. Write an equation, including state symbols, to show how one of these impurities can be removed by a Group 2 oxide.

When the gas sulfur dioxide, SO₂, reacts with water an acid is formed.

Draw the lewis diagram of the sulfur containing ion that is produced in this reaction and state the bond angle in the ion.

Excess aqueous sulfur dioxide, SO₂, can also react with sodium hydroxide solution, NaOH (aq), in an acid base reaction to form a sulfate (IV) salt in two stages.

Give both reactions, including state symbols, for the formation of the salt.

Phosphoric acid, P₄O₁₀ (aq), reacts with sodium hydroxide solution, NaOH (aq), to form a phosphate salt.

i) Write the overall equation for this reaction, including state symbols.

ii) Using oxidation numbers, state whether the reaction is a redox reaction.

The acid-base character of the Period 3 oxides changes from sodium to sulfur. In terms of electronegativity of the Period 3 element, explain why the acid-base character changes. 

Cola drinks contain phosphoric acid, H₃PO₄, which contributes to the taste of the drink. The acidic nature of the drink can also cause damage to tooth enamel.

A student took a 20% solution of cola which was boiled for 30 minutes using a heat plate and a magnetic stirrer and allowed to cool. They added small portions of 0.010 mol dm^-3 sodium hydroxide from a burette to 30.00 cm³ of the cola solution.

A pH meter recorded the pH of the initial solution and after every addition of sodium hydroxide. The student found that it took 12.05 cm³ of sodium hydroxide to neutralise the cola solution.

i) Suggest why the student boiled the cola solution before the experiment.

ii) Explain why would it not be suitable for an indicator to be used when carrying out this titration. 

Calculate the concentration of phosphoric acid, H₃PO₄, in the 20% sample of cola solution, and therefore in the original cola.

When phosphorus (V) oxide reacts with water it will produce phosphoric acid.

i) Write an equation to show the reaction between phosphoric acid and include the expected pH of the resulting solution.

ii) Explain why the melting point of phosphorus (V) oxide is relatively low compared to most other Period 3 oxides.