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

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:

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.

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.

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

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

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

Period 3 oxides all have different structure and bonding types.

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

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.

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.

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. 

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.

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.

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.