Ions & Ionic Bonds (Cambridge (CIE) O Level Chemistry): Exam Questions

Potassium iodide is an ionic compound. 

i) Describe what happens, in terms of electron loss and gain, when a potassium atom reacts with an iodine atom.

[2]

ii) Describe the structure of solid potassium iodide. You may draw a diagram.

[2]

iii) Explain why potassium iodide has a high melting point.

[2]

Potassium iodide and lead nitrate are both soluble. Lead iodide is insoluble.

i) Describe how a pure dry sample of lead iodide could be made from solid potassium iodide and solid lead nitrate.

 [4]

ii) Write an ionic equation for the formation of lead iodide, PbI₂, when potassium iodide and lead nitrate react with each other. State symbols are not required.

 [2]

When chlorine gas is bubbled through an aqueous solution of potassium iodide, a redox reaction takes place.

2I^– + Cl₂ → I₂ + 2Cl^– 

i) State the colour change expected in this reaction.

 start colour .............

 end colour ...............

  [2]

ii) Identify the reducing agent in this reaction. Explain your answer.

 [2]

Iron pyrite, FeS₂, is known as Fool’s Gold because it is a shiny yellow solid which is similar in appearance to gold. Iron pyrite is an ionic compound. Gold is a metallic element.

Iron pyrite, FeS₂, contains positive and negative ions. The positive ion is Fe²⁺. Deduce the formula of the negative ion.

A student is provided with a sample of iron pyrite and a sample of gold. Suggest how the student could distinguish between the two substances.

Sulfur dioxide is produced on a large scale by heating iron pyrite strongly in air. The iron pyrite reacts with oxygen in the air producing iron(III) oxide, Fe₂O₃, and sulfur dioxide.

Construct a chemical equation for the reaction between iron pyrite and oxygen.

Nitrogen can form ionic compounds with reactive metals and covalent compounds with non-metals.

Nitrogen reacts with lithium to form the ionic compound lithium nitride, Li₃N.

i) Write the equation for the reaction between lithium and nitrogen.

[2]

ii) Lithium nitride is an ionic compound. Draw a diagram which shows its formula, the charges on the ions and the arrangement of the valency electrons around the negative ion.

Use x for an electron from a lithium atom.

Use o for an electron from a nitrogen atom.

[2]

Nitrogen fluoride is a covalent compound.

i) Draw a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound nitrogen trifluoride, NF₃.

Use x for an electron from a nitrogen atom.

Use o for an electron from a fluorine atom.

[2]

ii) Lithium nitride has a high melting point, 813 °C. Nitrogen trifluoride has a low melting point, –207 °C.

Explain why the melting points are different.

[2]

The Group I metals show trends in both their physical and chemical properties.

i) How do their melting points vary down the Group?

[1]

ii) Which element in the Group has the highest density?

[1]

iii) All Group I metals react with cold water. Complete the following equation.

........Rb + ........H₂O → ................ + ................

[2]

Lithium reacts with nitrogen to form the ionic compound, lithium nitride.

i) State the formula of the lithium ion.

[1]

ii) Deduce the formula of the nitride ion.

[1]

iii) In all solid ionic compounds, the ions are held together in a lattice. Explain the term lattice.

[1]

iv) What is the ratio of lithium ions to nitride ions in the lattice of lithium nitride? Give a reason for your answer.

[2]

Table 1.1 shows the properties of four substances.

Table 1.1

State the meaning of the term ionic bonding.

Identify which information in Table 1.1 shows that potassium bromide is an ionic compound.

Magnesium, calcium and strontium are Group II elements

Magnesium reacts with chlorine to form magnesium chloride, MgCl_2.

Magnesium chloride is an ionic compound.

Complete the dot-and-cross diagram in Figure 1.1 of the ions in magnesium chloride.

Show the charges on the ions.

Figure 1.1

One physical property typical of ionic compounds, such as MgCl₂, is that they are soluble in water.

Give two other physical properties that are typical of ionic compounds.

Fluorine forms both ionic and covalent compounds.

Magnesium reacts with fluorine to form the ionic compound magnesium fluoride.

The electronic structures of an atom of magnesium and an atom of fluorine are shown.

Complete the dot-and-cross diagrams to show the electronic structures of one magnesium ion and one fluoride ion.

Show the charges on the ions.

Magnesium fluoride does not conduct electricity when it is solid.

What can be done to solid magnesium fluoride to make it conduct electricity?

In your answer explain why magnesium fluoride conducts electricity when this change is made.

The melting points of magnesium fluoride and carbonyl fluoride are shown.

Explain, using your knowledge of structure and bonding, why magnesium fluoride has a high melting point.

Magnesium exists as three isotopes, ,  and .

Magnesium reacts with oxygen to form the ionic compound magnesium oxide.

Complete the dot-and-cross diagrams to show the electronic structures of the ions in magnesium oxide.

Show the charges on the ions.

Magnesium oxide melts at 2853 °C.

Why does magnesium oxide have a high melting point?

Explain why molten magnesium oxide can conduct electricity.

Copper(II) chloride, copper(II) iodide and copper(II) carbonate are ionic compounds.

Predict two physical properties, other than electrical conductivity, of copper(II) chloride.

Copper is a transition element. Suggest one property of copper(II) chloride that is characteristic of a compound of a transition element.

Copper reacts with chlorine to make copper(II) chloride.

Cu + Cl₂ → CuCl₂

Copper(II) chloride contains Cu²⁺ and Cl^– ions.

Explain, in terms of the movement of electrons, how CuCl₂ is formed from copper atoms and chlorine molecules.

Copper(II) iodide decomposes to make iodine and copper(I) iodide. The ionic equation for this reaction is shown.

2Cu²⁺ + 4I^– → 2CuI + I₂

i) Use the information to explain that oxidation takes place.

[1]

ii) Use the information to explain that reduction takes place

[1]

A sample of copper(II) carbonate is heated strongly. Name the products of this reaction.

Calcium chloride, CaCl₂, is an ionic compound.

Deduce the electronic configuration for each of the ions in calcium chloride.

When molten calcium chloride is electrolysed with inert electrodes, calcium and chlorine are formed. Construct ionic half-equations for the two electrode reactions.

The electrolysis of concentrated aqueous calcium chloride with inert electrodes is similar to that of concentrated aqueous sodium chloride. Predict the products of the electrolysis of concentrated aqueous calcium chloride with inert electrodes.

Calcium chloride has a high melting point. Explain why calcium chloride has a high melting point. Use ideas about structure and bonding.

The first three elements in Period 6 of the Periodic Table of the Elements are caesium, barium and lanthanum.

How many more protons, electrons and neutrons are there in one atom of lanthanum than in one atom of caesium. Use your copy of the Periodic Table of the Elements to help you.

Number of protons =

Number of electrons = 

Number of neutrons =

Extended Only

All three metals can be obtained by the electrolysis of a molten halide. The electrolysis of the aqueous halides does not produce the metal.

i) Complete the equation for the reduction of lanthanum ions at the negative electrode (cathode).

La³⁺ + ................ → ................

[1]

ii) Name the three products formed by the electrolysis of aqueous caesium bromide.

[3]

All three metals react with cold water. Complete the word equation for these reactions.

metal + water → ................................. + .............................

Barium chloride is an ionic compound. Draw a diagram that shows the formula of the compound, the charges on the ions and gives the arrangement of the valency electrons around the negative ion.

The electron distribution of a barium atom is 2.8.18.18.8.2

Use x to represent an electron from a barium atom.

Use o to represent an electron from a chlorine atom.

Extended Only 

Describe, by means of a simple diagram, the lattice structure of an ionic compound, such as caesium chloride.

Extended Only 

The reactions of these metals with oxygen are exothermic.  

2Ba (s) + O₂ (g) → 2BaO (s)

i) Give an example of bond forming in this reaction.

[1]

ii) Explain using the idea of bond breaking and forming why this reaction is exothermic.

[3]

Calcium reacts with nitrogen to form the ionic compound calcium nitride, Ca₃N₂.

Draw a diagram, based on the correct formula, which shows the charges on the ions and the arrangement of the electrons around the negative ion.

Use o to represent an electron from a calcium atom. Use x to represent an electron from a nitrogen atom.

Extended Only 

In the lattice of calcium nitride, the ratio of calcium ions to nitride ions is 3 : 2.

i) What is meant by the term lattice?

[2]

ii) In terms of ionic charges, explain why the ratio of ions is 3 : 2.

 [2]

Extended Only 

The reaction between calcium and nitrogen to form calcium nitride is a redox reaction. In terms of electron transfer, explain why calcium is the reducing agent.

Extended Only 

The diagram shows the lattice of a typical ionic compound.

i) Explain the term ionic lattice.

[2]

ii) In this lattice, the ratio of positive ions to negative ions is 1:1. In the lattice of a different ionic compound, the ratio of positive ions to negative ions is 1:2. Suggest why this ratio varies in different ionic compounds.

 [1]

iii) Give three physical properties of ionic compounds.

[3]

Extended Only 

Strontium oxide is an ionic compound.

Draw a diagram which shows its formula, the charges on the ions and the arrangement of the valency electrons around the negative ion.

The electron distribution of a strontium atom is 2 + 8 + 18 + 8 + 2. Use o to represent an electron from a strontium atom.
Use x to represent an electron from an oxygen atom.

The structure of an element or compound determines its physical properties. Scandium fluoride and silicon(IV) oxide have giant structures.

Scandium fluoride is an ionic compound.

i) The valency of scandium is three. Draw a diagram which shows the formula of the compound, the charges on the ions and the arrangement of the valency electrons around the negative ion.

Use x to represent an electron from a scandium atom. Use o to represent an electron from a fluorine atom.

[3]

ii) The melting point of scandium fluoride is 1552 °C. Explain why scandium fluoride has a high melting point.

[1]

Silicon(IV) oxide has a macromolecular structure.

i) Describe the structure of silicon(IV) oxide. You may use a diagram.

[3]

ii) How does the electrical conductivity of these two compounds differ?

[1]

iii) Explain the difference in conductivity.

[2]

Both strontium and sulfur have chlorides of the type XCl₂. The table below compares some of their properties.

i) Use the data in the table to explain why sulfur chloride is a liquid at room temperature, 25 °C.

[2]  

ii) Strontium is a metal and sulfur is a non-metal. Explain why both have chlorides of the type XCl₂. The electron distribution of a strontium atom is 2 + 8 + 18 + 8 + 2.

[2]

iii) Explain the difference in the electrical conductivity of liquid strontium chloride and liquid sulfur chloride.

[3]

Strontium chloride-6-water can be made from the insoluble compound, strontium carbonate, by the following reactions.

SrCO₃ (s) + 2HCl (aq) → SrCl₂ (aq) + CO₂ (g) + H₂O (l)

SrCl₂ (aq) + 6H₂O (l) → SrCl₂.6H₂O (s)

The following method was used to prepare the crystals.

1.  Add excess strontium carbonate to hot hydrochloric acid.
2.  Filter the resulting mixture.
3.  Partially evaporate the filtrate and allow to cool.
4.  Filter off the crystals of SrCl₂.6H₂O.
5.  Dry the crystals between filter papers.

i) How would you know when excess strontium carbonate had been added in step 1?

[1]

ii) Why is it necessary to filter the mixture in step 2?

[1]

iii) In step 3, why partially evaporate the filtrate rather than evaporate to dryness?

[1]

In the above experiment, 50.0 cm³ of hydrochloric acid of concentration 2.0 mol / dm³ was used. 6.4 g of SrCl₂.6H₂O was made.  

Calculate the percentage yield.  

number of moles of HCl used = ............................

number of moles of SrCl₂.6H₂O which could be formed = ............................

mass of one mole of SrCl₂.6H₂O is 267 g

theoretical yield of SrCl₂.6H₂O = ............................g

percentage yield = ............................%