Group VII Properties (Cambridge (CIE) O Level Chemistry): Exam Questions

Three of the halogens in Group VII are listed below, with their colours at room temperature and pressure.

i) How does their colour change down the Group?

[1]

ii) How does their density change down the Group?

[1]

iii) Predict the colour and physical state (solid, liquid or gas) of astatine, At.

[2]

A radioactive isotope of iodine, ${}_{53}{}^{131}\mathrm{I}$, is used to treat cancer.

i) Define the term isotope.

[2]

ii) How many protons, electrons and neutrons are there in one atom of ${}_{53}{}^{131}\mathrm{I}$

number of protons ..............

number of electrons ............

number of neutrons ............

[2]

iii) When this isotope, ${}_{53}{}^{131}\mathrm{I}$, emits radiation, a different element with a proton number of 54 is formed. What is the name of this element?

[1]

Fluorine, the most reactive halogen, forms compounds with the other halogens.

It forms two compounds with bromine. Deduce their formulae from the following information.

compound 1: the mass of one mole of this compound is 137 g

[1]

compound 2: 0.02 moles of this compound contain 0.02 moles of bromine atoms and 0.1 moles of fluorine atoms

[1]

Table 1 shows some properties of some of the halogens.

Table 1

Use the information in Table 1 to suggest:

• the colour of astatine

• the boiling point of bromine

• the state of iodine at 190 °C

Aqueous chlorine reacts with aqueous potassium bromide as shown.

Cl₂ + 2KBr → Br₂ + 2KCl

Name the salt formed in this reaction.

Explain why aqueous bromine does not react with aqueous potassium chloride.

Complete the dot-and-cross diagram in Figure 1 of a molecule of chlorine.
Show outer shell electrons only.

Figure 1

This question is about the elements in Group VII of the Periodic Table, and their compounds.

State the general name given to the elements in Group VII.

Chlorine gas is bubbled through aqueous potassium bromide. A displacement reaction occurs.

i) State one observation that is made during this reaction.

[1]

ii) Predict whether a reaction would occur if aqueous iodine is added to aqueous potassium bromide instead of chlorine. Explain your reasoning.

prediction

explanation

[2]

Chlorine reacts with methane, CH₄, in a substitution reaction.

i) State the essential condition required for this reaction to happen.

[1]

ii) The chemical equation for the reaction is shown.

CH₄ (g) + Cl₂ (g) → CH₃Cl (g) + HCl (g)

Some bond energies are given in Table 5.1.

Table 5.1

Calculate the enthalpy change for this reaction. Show your working. Use the following steps:

• Calculate the energy needed to break the bonds, in kJ/mol

• Calculate the energy released in forming the bonds, in kJ/mol

• Determine the overall enthalpy change for the reaction, in kJ/mol

[3]

PVC is an addition polymer that contains chlorine.

The structure of PVC is shown in Fig 5.1.

Fig 5.1

Draw the displayed formula of the monomer used to make PVC. Show all of the atoms and all of the bonds.

The halogens are a collection of diatomic non-metals in Group VII.

i) Define the term diatomic.

[1]

ii) What do the electron distributions of the halogens have in common?

[1]

iii) How do their electron distributions differ?

[1]

iv) Complete the table.

[2]

The halogens react with other non-metals to form covalent compounds.

Draw a diagram which shows the arrangement of the valency electrons in one molecule of the covalent compound arsenic trifluoride.

The electron distribution of an arsenic atom is 2 + 8 + 18 + 5.

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

Photochromic glass is used in sunglasses. In bright light, the glass darkens reducing the amount of light reaching the eye. When the light is less bright, the glass becomes colourless increasing the amount of light reaching the eye.
Photochromic glass contains very small amounts of the halides silver(I) chloride and copper(I) chloride. The reaction between these two chlorides is photochemical.

How does photochromic glass work?

Three of the halogens in Group VII are listed below, with their appearance at room temperature and pressure.

i) How does their colour change down the Group?

[1]

ii) Predict the colour and physical state of fluorine.

Colour ....................

Physical state ....................

[2]

Describe how you could distinguish between aqueous potassium bromide and aqueous potassium iodide.

Test ....................

Result with bromide ............................................................

Result with iodide ............................................................

0.015 moles of iodine react with 0.045 moles of chlorine to form 0.030 moles of a single product.

Complete the equation.

I₂ + ............ Cl₂ → ................................

Traces of chlorine can be separated from bromine vapour by diffusion.

Which gas would diffuse the faster and why?

Trends can be observed in the way Group I and Group VII elements react. 

Suggest why Group I elements lithium, sodium and potassium are all stored in paraffin oil.

Caesium, Cs, is below potassium in Group I.

i) Give a similarity and a difference between the reactions of potassium with water and caesium with water.

similarity..........................................................

difference........................................................

[2]

ii) Give the chemical equation for the reaction between caesium and water.

[2]

Table 5.1 gives some information about the halogens.

Complete the table by predicting the physical state of astatine at room temperature and the colour of astatine.

Table 5.1

A student investigates the reactivity of some halogens.

She uses these solutions of halogens and their halides.

• bromine, chlorine and iodine

• sodium bromide, sodium chloride and sodium iodide

She adds each halogen solution to each halide solution.

Table 5.2 shows her results.

Table 5.2

i) Explain how these results show the order of reactivity of bromine, chlorine and iodine.

[3]

ii) Suggest why the student does not need to add bromine solution to sodium bromide solution.

[1]

iii) The ionic equation for the reaction between bromine and sodium iodide is

Br₂ (aq) + 2I⁻ (aq) → I₂ (aq) + 2Br⁻ (aq)

Explain why this is a redox reaction.

[2]