Atoms & Reactions (OCR A Level Chemistry A): Exam Questions

Atoms are made up of three subatomic particles; protons, neutrons and electrons.

Using the data and the Periodic Table, calculate the mass of one atom of carbon in kg.

¹²C, ¹³C and ¹⁴C are all isotopes of carbon.

State the difference between these three isotopes in terms of subatomic particles.

A student claims that the different isotopes of carbon will have different chemical properties. 

Is the student correct? Explain your answer.

Data on the relative isotopic abundance of a chemical element, E, is shown. 

 i) Complete the table by calculating X.

ii) Use the data from the table and the Periodic Table to calculate the relative atomic mass, A_r, to 1 decimal place and identify element, E.

The Bohr model of an atom represents a central nucleus, consisting of protons and neutrons, with electrons surrounding it moving in circular orbits. 

This model was proposed by Niels Bohr in 1913 and after some further research, energy levels and sublevels were recognised, and the model was refined.  

Using your knowledge of atomic structure, complete the table for the particles found in an atom. 

State the block in the Periodic Table in which silicon is placed and explain your answer.

The graph shows the mass spectrum of a sample of silicon. 

Calculate the relative atomic mass, A_r, of this sample of silicon to 1 decimal place.

Suggest why the relative atomic mass on the Periodic Table might be different to the relative atomic mass of a sample analysed using a mass spectrometer. 

Geraniol is a colourless oil containing two carbon-carbon double bonds and one other functional group. It is the main component of citronella oil with low water solubility, but it is soluble in common organic solvents.

State the other functional group present in geraniol.

The mass spectrum of geraniol is shown below.

Deduce the relative molecular mass of geraniol.

A molecular formula of C₇H₅₄O is proposed for geraniol.

i) Using your answer to part (b), suggest one reason why this molecular formula is possible.

ii) Suggest one reason why this molecular formula is not possible.

Using your previous answers, suggest a molecular formula for geraniol.

Silicon is a hard, brittle, blue-grey crystalline semiconductor. It is also described as a tetravalent metalloid.

State the formulae of two common silicon ions.

The silicate ion is analogous to the carbonate ion.

Suggest the formula of the silicate ion.

Write a balanced ionic equation to show the formation of aluminium silicate.

Calcium silicate can be used to store or trap carbon dioxide.

Write a balanced symbol equation for this reaction showing the formation of two solid products.

A and B are different chemical elements, from different groups in the Periodic Table.

State why ^mA and ⁿA have identical chemical properties, but ^mA and ^pB have different chemical properties. 

An atom has twice as many protons, and twice as many neutrons, as an atom of ¹⁹F. 

Determine the chemical symbol for this atom, including the mass number, and deduce the number of electrons.

Name an instrument which would be used to measure the relative abundances of isotopes of an element

Explain the graph which would be produced when measuring the relative abundances of isotopes in an element.

Describe how the graph and data obtained can be used to calculate the relative atomic mass of the element in question.

In this part, you need to refer to the Periodic Table of the Elements in the Data Sheet. 

From the first 18 elements only, choose an element which fits the following descriptions:

i) An element with an isotope that can be represented as 

[1]

ii) The element which forms a Z^2– ion with the same electron structure as Ar.

[1]

iii) The element in Period 3 with the first four successive ionisation energies shown below, in kJ mol^–1.

577 1820 2740 11600

[1]

A sample of element G was extracted from a meteorite. Table 1 shows the relative abundance of each isotope in a mass spectrum of this sample of G. Calculate the relative atomic mass of G and suggest an identity of G. Give your answer to 1 d.p.

Table 1

Sometimes in the mass spectrum on G a very small peak with an m/z value of 32 is present. Explain the occurrence of this peak.

Element G can be alloyed with tin and lead to make solder. Lead exists as four isotopes shown in Table 2 and has an A_r value of 207.241.

Calculate the relative isotopic mass of W. Give your answer to 3 significant figures.

Table 2

Oxyacids of chlorine include, HClO, HClO₂, HClO₃ and HClO₄.

An acid base reaction occurs between a solution of HClO₄ is added to a solution of strontium hydroxide.

Write a balanced symbol equation for this reaction including state symbols.

Chlorine has two naturally occurring isotopes. ³⁵Cl with a mass of 34.969 and ³⁷Cl with a mass of 36.966.

The relative atomic mass of Cl is 35.5. Calculate the abundance of each isotope to 2 d.p. 

Predict the size of the atomic radius of ³⁵Cl relative to the atomic radius of ³⁷Cl would be the largest. Explain your answer.

Borax is one of the most important compounds of boron. The formula of anhydrous borax is Na₂B₄O₇. 

Anhydrous borax produces a sodium hydroxide and orthoboric acid, H₃BO₃, when dissolved in water.

Write an equation for this reaction.

A naturally occurring sample of the element boron, B, has two isotopes ¹⁰B and ¹¹B and a relative atomic mass of 10.8.

i) State the definition of relative isotopic mass.

[2]

ii) Calculate the relative abundances of both isotopes in the sample of boron, B.

[3]

Hydrated borax powder has the formula Na₂B₄O₇.xH₂O when 2.12 g of hydrate is heated in a crucible until a constant mass is reached. The mass of the anhydrous Na₂B₄O₇ salt is 1.11 g. Calculate the value of x and therefore deduce the name of hydrated borax powder.

Sulfur, S₈, is a yellow solid that can react with nitric acid to form sulfuric acid, a brown gas, and water.

Write a balanced symbol equation for this reaction.

Sulfur exists as four isotopes and has a relative atom mass of 32.0928.

Figure 1 shows the relative intensities of three of these isotopes. The total relative abundance is 94.99. 

Figure 1

Calculate the relative isotopic mass of the fourth isotope of sulfur.

Predict and explain whether or not the isotopes of sulfur would have the same chemical properties.

Copper is an easily moulded base metal that is often added to precious metals to improve their elasticity, flexibility, hardness, colour, and resistance to corrosion.

Table 1 shows the number of protons, neutrons and electrons of different isotopes and ions of copper.

Table 1

i) Complete Table 1.

[2]

ii) Give the full electron configuration of the Cu⁺ ion. 

[1]

Calculate the percentage abundance of ⁶³Cu with a mass of 62.9296 and ⁶⁵Cu with a mass of 64.9278, when the average mass of the Cu isotope is 63.546.

Give your answer to an appropriate number of significant figures.

Copper can form a salt with chlorine to form copper(II) chloride. This reacts with sodium phosphate to form two different salts only.

Write a balanced equation for this reaction.