Edexcel GCSE Combined Science Paper 4: Chemistry 2 Higher June 2018 question paper 1SC0/2CH

The Earth’s atmosphere contains several gases.

Figure 1 shows the relative amounts of gases thought to be in the Earth’s early atmosphere.

The amount of water vapour in today’s atmosphere is much less than the amount in the Earth’s early atmosphere.

Explain why the amount of water vapour in the atmosphere has decreased.

The apparatus shown in Figure 2 is used to find the percentage of oxygen in dry air.

Syringe A contains 50 cm³ of dry air and syringe B contains no air. The copper in the glass tube is heated strongly. The air in the apparatus is passed backwards and forwards over the copper until all the oxygen has been removed.

The following results were obtained

initial volume of air in apparatus = 50 cm³

final volume of gas in apparatus = 40 cm³

Calculate the percentage of oxygen in this sample of dry air.

percentage oxygen in the air =_........

At the end of the experiment, the apparatus and its contents are allowed to cool before the final volume of gas is measured.

The apparatus and its contents must be allowed to cool because

The Earth’s earliest rocks contained iron sulfide and no iron oxide. Later the rocks contained iron oxide as well as iron sulfide.

Explain what happened to allow this change to occur.

(a) A chlorine atom contains 17 electrons, 18 neutrons and 17 protons.

State the mass number of this chlorine atom.

Give the electronic configuration of this chlorine atom.

Describe what you would see if damp, blue litmus paper is placed into chlorine gas.

Chlorine exists as diatomic molecules.

In a molecule, two chlorine atoms are joined by a covalent bond.

Describe what is meant by a covalent bond.

Explain why chlorine is a gas, rather than a liquid, at room temperature.

When the gas hydrogen chloride, HC l, is dissolved in water, a solution forms. Blue litmus paper dipped in this solution turns red.

State why the litmus paper turns red.

Lithium, sodium and potassium are reactive metals in group 1 of the periodic table.

Sodium metal tarnishes in air to form a layer of sodium oxide on its surface. 0.92 g of sodium combined with 0.32 g of oxygen in this oxide.

Calculate the empirical formula of this sodium oxide. (relative atomic masses: O = 16, Na = 23)

You must show your working.

empirical formula of sodium oxide =_........

Sodium reacts with water to form sodium hydroxide solution and hydrogen.

Complete the balancing of the equation for this reaction and add the state symbols for each substance.

_........ Na(_........ ) + 2H₂O(_........ ) _........ NaOH(_........ ) + H₂(_........ )

In an experiment equal-sized pieces of lithium, sodium and potassium are added to separate samples of water.

A flame is produced only with potassium because potassium

Explain, in terms of electronic configurations, the increase in reactivity from lithium to sodium to potassium.

Crude oil is a complex mixture of substances.

Crude oil can be separated into useful fractions by fractional distillation.

Figure 3 shows a fractional distillation column and the fractions produced when a sample of crude oil is distilled.

The properties of these fractions vary from the top of the column to the bottom of the column.

Which of the following is a trend in a property of the fractions obtained from the top of the column to those obtained from the bottom?

Most of the substances in crude oil are alkanes.

Which of the following is the general formula of an alkane?

Explain why alkanes are described as hydrocarbons.

Figure 4 shows a graph of the boiling points of some alkanes against the number of carbon atoms in one molecule of each alkane.

Explain the pattern shown by this graph.

Use the information in Figure 5 to give the name of the fraction that is most likely to need to be cracked.

_........

In a cracking reaction, reactants are heated to form products. This reaction is endothermic.

On the axes provided, draw the reaction profile of this reaction. Label the energy of the reactants, the energy of the products and the activation energy of the reaction.

Dodecane, C₁₂H₂₆, can be cracked to form useful products.

Complete the equation for the cracking of dodecane by filling in the formula of the single molecule needed to balance the equation.

C₁₂H_{26 ........} + 3C₂H₄

Describe what is seen when chlorine water is added to potassium bromide solution and the mixture shaken.

Chlorine reacts with potassium bromide to form potassium chloride and bromine. In this reaction chlorine forms chloride ions

In this reaction, chlorine has been reduced.

Explain, using the equation, how you know that chlorine has been reduced.

Write the half equation for the formation of bromine from bromide ions.

Aluminium reacts with chlorine to form aluminium chloride.

Write the balanced equation for this reaction.

A solid ionic compound is dissolved in water to form a solution.

Describe a simple experiment to show that charged particles are present in this solution.

(a) The rate of reaction between magnesium ribbon and dilute hydrochloric acid at room temperature is investigated.

The apparatus used is shown in Figure 6.

The volume of hydrogen gas given off was measured at regular intervals during the reaction.

The graph in Figure 7 shows the results of this experiment.

State a change that can be made to the apparatus in Figure 6 to measure the volumes of gas more accurately.

A tangent has been drawn to the line on the graph in Figure 7.

Calculate the rate of reaction at this point.

rate of reaction =_........ cm s

On the graph in Figure 7, draw the line you would expect to obtain if the magnesium ribbon in this experiment was replaced with an equal mass of powdered magnesium. All other conditions are kept the same.

The balanced equation for this reaction is

In another experiment, 0.1 moles of hydrochloric acid, HC l, were reacted with 0.1 g of magnesium ribbon.

Calculate the number of moles of magnesium, Mg, in the 0.1 g sample of magnesium ribbon. (relative atomic mass: Mg = 24)

number of moles =_........

In a further experiment, 0.5 mol of hydrochloric acid, HC l, were mixed with 0.5 mol of magnesium, Mg.

Use the equation to show that, in this experiment, the magnesium is in excess.

*(c) Two substances, A and B, each form a colourless solution. If the solutions are mixed in a beaker, A and B react to form a coloured product. The rate of the reaction between A and B can be investigated by placing the beaker containing the mixture on a cross on a piece of paper and timing how long it takes for enough coloured product to be produced to make the cross invisible when viewed from above, through the solution.

Use the results of these experiments to explain, in terms of the behaviour of particles, the effect of changing temperature and the effect of changing the concentration of A in solution on the rate of this reaction.