Edexcel GCSE Combined Science Paper 4: Chemistry 2 Higher November 2020 question paper 1SC0/2CH

An atom of potassium has atomic number 19 and mass number 39.

Give the electronic configuration of this potassium atom.

This potassium atom forms the ion K⁺.

Which row shows the number of protons and the number of neutrons in this potassium ion, K⁺?

Potassium and caesium are in the same group of the periodic table.

Explain, in terms of electrons, why potassium and caesium are in the same group.

Fluorine boils at –188C. There are forces between fluorine molecules.

Explain, in terms of these forces, why the boiling point of fluorine is low.

Potassium reacts with fluorine to form potassium fluoride. Potassium fluoride is a solid.

Complete the balanced equation for this reaction and add the state symbols.

_........ K (_........ ) + F₂(g) _........ KF (_........ )

Calcium carbonate reacts with dilute hydrochloric acid to produce carbon dioxide gas.

The rate of reaction between calcium carbonate and dilute hydrochloric acid at room temperature was investigated.

The investigation was carried out with different sized calcium carbonate pieces.

The mass of calcium carbonate and all other conditions were kept the same.

The results are shown in Figure 1.

State, using the information in Figure 1, the effect of the surface area of the calcium carbonate on the rate of this reaction.

The calcium carbonate powder produced 90 cm³ of carbon dioxide in five minutes.

Calculate the average rate of reaction in cm³s^–1.

average rate of reaction =_........ cm³s^–1

The experiments were repeated at a higher temperature. The rate of reaction for each experiment increased.

Explain, in terms of particles, why the rate of reaction increased when the temperature was increased.

Sodium thiosulfate solution, Na₂S₂O₃, reacts with dilute hydrochloric acid.

When dilute hydrochloric acid is mixed with sodium thiosulfate solution, the mixture turns cloudy.

Explain why the mixture turns cloudy.

In an investigation, different concentrations of hydrochloric acid are reacted with sodium thiosulfate solution. The mixture goes cloudy at different rates.

Describe how the rate at which the mixture goes cloudy can be measured.

You are provided with some dilute hydrochloric acid which has a concentration of 50 g dm^–3.

For this experiment, dilute hydrochloric acid with a concentration of 20 g dm^–3 is required.

How much water must be added to 100 cm³ of 50 g dm^–3 hydrochloric acid to make dilute hydrochloric acid with a concentration of 20 g dm^–3?

Sodium iodide solution is colourless.

When a solution of bromine is added to sodium iodide solution, a reaction occurs.

The mixture turns brown.

Give the name of the substance causing the brown colour.

Explain which substance has been reduced in this reaction.

Air contains several gaseous elements.

Which of these shows the three most common gaseous elements in air, listed in order from the most common to the least common?

The density of a gas can be found using the equation

A student carried out an experiment to find the density of argon.

The mass of a stopper and flask, containing no gas, was known. The flask was completely filled with argon and its mass measured.

Figure 2 shows the results the student wrote down.

Use the results to calculate the density of argon in g cm^–3.

density of argon =_........ g cm^–3

The flask used for the experiment is shown in Figure 3. The flask holds 250.0 cm³ when filled up to the line.

There is an error in the volume the student has used in the calculation. This would give an incorrect value for the density of argon.

Identify this error and state what should be done to correct it.

error_........

what should be done to correct it_........

Four of the noble gases are argon, helium, krypton and neon.

Give these gases in order of increasing density.

Much of the carbon dioxide present in the Earth’s early atmosphere dissolved into the oceans.

This led to the formation of compounds including calcium carbonate, CaCO₃.

Some of the calcium carbonate reacted with magnesium ions to form dolomite, CaMg(CO₃)₂.

Complete the ionic equation for the reaction of calcium carbonate with magnesium ions.

_........ CaCO₃ +_........ CaMg(CO₃)₂ + Ca²⁺ dolomite

P and Q are both mixtures of gases. One has the same composition as the early atmosphere and the other has the same composition as the current atmosphere.

Tests are carried out on gas mixtures P and Q.

The test for carbon dioxide is to bubble the gas into limewater; if carbon dioxide is present calcium carbonate is formed.

The results of the tests are shown in Figure 4.

Explain, using the data in Figure 4, which gas mixture represents the early atmosphere.

The first four elements in group 1 are lithium, sodium, potassium and rubidium.

Rubidium reacts with water to form rubidium hydroxide and hydrogen.

Predict what you would see when a small piece of rubidium is placed in a large volume of water.

Why is rubidium more reactive than potassium?

8.5 g of rubidium are reacted completely with water.

The reaction makes a solution of rubidium hydroxide. The volume of this solution is 2.5 dm³.

Calculate the concentration of the rubidium hydroxide solution in g dm^–3.

(relative atomic mass: Rb = 85; relative formula mass: RbOH = 102)

concentration =_........ g dm^–3

An example of an endothermic reaction is the reaction between rubidium hydroxide and ammonium carbonate, (NH₄)₂CO₃.

This reaction forms rubidium carbonate, Rb₂CO₃, ammonia and one other product.

Write the balanced equation for this reaction.

An impure hydrocarbon fuel is burned in the apparatus in Figure 5.

When the fuel is burned

the funnel becomes hot a colourless liquid forms in tube A the indicator in tube B changes colour to show an acidic gas.

Explain these observations.

The energies of some bonds are shown in Figure 6.

Methane burns in oxygen to form carbon dioxide and water.

The equation shows the structures of the molecules.

Calculate the energy change, in kJ mol^–1, for this reaction.

energy change =_........ kJ mol^–1

*(c) Petrol and diesel are used as fuels for cars. The emissions from three similar sized cars were investigated. The first car was the oldest, had no catalytic converter and used petrol. The other two cars were only a few years old. One of these was fitted with a catalytic converter and used petrol and the other car used diesel.

Figure 7 shows the emissions in grams for each kilometre travelled by these three cars.

Discuss and compare the impact on the environment of the emissions from these three cars using the information from Figure 7.