OCR GCSE Chemistry B (21st Century) Paper 2 November 2020 question paper

Fig. 1.1 shows the dot and cross diagrams for some molecules.

Which molecules are elements and which are compounds?

Tick (✓) one box in each row.

How do the dot and cross diagrams in Fig. 1.1 show that all of these molecules are simple covalent?

Tick (✓) two boxes.

How does the dot and cross diagram in Fig. 1.1 show that carbon dioxide has double bonds?

Using Fig. 1.1, complete the table to show how many bonds each atom forms.

Argon is a gas. The arrangement of electrons in the outer shell of argon is shown in Fig. 1.2

Explain how and why argon is different to the simple covalent molecules shown in Fig. 1.1

Nina works for a company that makes pH meters.

She makes up four solutions A, B, C and D. Each solution has a different, known pH.

Table 2.1 shows the pH of each solution.

Nina tests three pH meters to find out if they measure pH accurately.

She uses the three pH meters to measure the pH of solutions A, B, C and D. She dips each pH meter into each solution and takes a reading.

Nina washes each pH meter between readings.

Explain why it is important that she does this.

Nina wants to use another method to measure pH.

What other method could she use to measure pH?

Tick (✓) one box.

Explain why scientists often use more than one method to collect results when they do experiments.

Crude oil is a mixture of mainly alkanes.

All alkanes have this general formula:

Explain how this formula shows that alkanes are hydrocarbons.

Crude oil also contains a small amount of other molecules that are not alkanes.

The table shows the formulae of three molecules in crude oil.

Explain your answers.

Use the general formula for alkanes to help you.

C₈H₁₈ is / is not an alkane

because........

C₃H₈S is / is not an alkane

because........

C₆H₁₂ is / is not an alkane

because........

Beth does an experiment to measure the rate of reaction between zinc pieces and dilute hydrochloric acid.

When dilute hydrochloric acid reacts with zinc a gas is made.

This is the word and symbol equation for the reaction between zinc and dilute hydrochloric acid.

What is the name of the gas that is made in this reaction?

Beth uses this apparatus to collect and measure the amount of gas that is made.

Complete the diagram to show how the gas is collected.

Beth does a control experiment first. She then repeats her experiment three times.

For each experiment, she measures the time taken for 50.0 cm³ of gas to be made. She changes one variable for each experiment.

Table 4.1 shows her results.

What conclusions can you make about the effects of changing each variable on the rate of the reaction?

Use the data in Table 4.1 to explain your reasons.

Concentration of Acid........

Temperature........

Surface Area........

Beth repeats her control experiment, but now adds a small amount of catalyst to the reaction mixture.

How does adding a catalyst affect the reaction?

Tick (✓) two boxes.

* Describe how magnesium and oxygen atoms form ions, and explain the charges on each ion.

Use ideas about electrons and electron shells in your answer.

The table shows the melting point and boiling point of magnesium oxide and some other oxides.

Room temperature is 20 °C.

Draw lines to connect each oxide with its correct state and state symbol (at room temperature).

Complete the sentences to explain the differences between the melting points of the three oxides.

Use words from the list.

Each word can be used once, more than once, or not at all.

magnesium oxide
strong

carbon monoxide
covalent

water ionic

weak intermolecular

The oxide with the highest boiling point is........

The oxide with the lowest melting point is........

The melting point is low because the forces between molecules are very........

These forces are called........ forces.

The type of bonding between atoms in carbon monoxide and water is

........

Eve heats magnesium ribbon in a crucible.

Complete the word equation and balance the symbol equation for the reaction that happens in the crucible.

Eve writes down the mass of the empty crucible, and the mass of the crucible and magnesium oxide at the end of the experiment.

She also works out how much magnesium oxide she expects to make (her theoretical yield

Complete Table 6.1 by calculating the mass of magnesium oxide formed in Eve’s experiment.

Eve works out her percentage yield, using the equation:

Calculate the percentage yield in Eve’s experiment.

Use the data in Table 6.1, and the equation provided.

Give your answer to 2 significant figures.

Eve does some more experiments.

She measures the mass of magnesium oxide formed when different masses of magnesium are heated.

Plot a graph of magnesium oxide formed against mass of magnesium heated.

Use the data in Table 6.2.

You should include on your graph:

• an appropriate scale for your axes

• a line of best fit.

Eve thinks that she wrote down the results for one of her experiments before the reaction had fully finished.

Suggest which reaction had not fully finished.

Use your graph to explain your answer.

Reaction........

Explanation........

Drain cleaner removes blockages in shower drains.

Drain cleaner contains solid sodium hydroxide.

An exothermic reaction happens when the solid sodium hydroxide dissolves in water in the drain. This helps to clear the blockage.

The diagram shows the energy change of the reaction when solid sodium hydroxide dissolves in

How does the diagram show that this reaction is exothermic ?

Tick (✓) two boxes.

Kai does an experiment to prove that when solid sodium hydroxide dissolves in water, an exothermic reaction happens.

Write an outline plan for Kai’s experiment.

The plan should include:

• what Kai should do

• what measurements he should make

• what results he should expect.

This is the hazard warning symbol for solid sodium hydroxide.

Kai wears gloves and goggles when he does his experiment.

Explain why these are necessary.

A company sets up three monitoring stations to measure the concentration of sulfur dioxide in the air around a coal-fired power station.

Why does the company set up three monitoring stations rather than only one?

There is a motorway with a lot of traffic near the power station.

The company makes sure that the monitoring stations are not set up near the motorway.

Explain one reason why this is important.

Suggest one other factor the company should consider when deciding where to set up the monitoring stations.

* The power station burns the same amount of coal every day.

The table shows the mean concentration of sulfur dioxide in the air and the weather conditions near the power station over 6 days.

Describe how the concentration of sulfur dioxide in the air changes over the week, and suggest reasons for the changes.

Use the information in the table to support your answer.

Amaya and Li discuss the PET symbol.

Do you agree with each person’s comments?

Give one reason for each of your answers.

Amaya........

Li........

If glass bottles are used instead of PET bottles, the bacteria are not killed.

Suggest why bacteria in water in a glass bottle are not killed.

In the UK, bacteria in drinking water are killed by adding a substance to the water.

Name this substance.

Which stage of the flowchart produces pure PET?

Waste PET bottles that are used to treat water are removed from the process before the end.

After which stage should bottles that are used to treat water be removed?

Using waste PET bottles to treat water or to make padding for jackets are two examples of ways to reduce mixed plastic waste.

Explain the difference between reusing and recycling PET bottles, using these two examples.

Waste PET bottles used to treat water and to make padding for jackets have different Life Cycle Assessments.

Give two reasons why their Life Cycle Assessments are different.

Sundip passes electricity through solutions of some ionic compounds and finds out what products are formed at the positive and negative electrodes.

Here are Sundip’s results.

Complete the table by predicting the products formed at each electrode when electricity

is passed through concentrated copper chloride and dilute sodium sulfate.

Sundip uses tests to identify the gases formed in her experiments.

Draw lines to connect each gas to its correct test and result.

Explain why, at the negative electrode:

• copper metal is formed when electricity is passed through dilute copper chloride, but

• hydrogen gas is formed when electricity is passed through dilute sodium chloride.

This is a list of apparatus Sundip uses to pass electricity through the solution of dilute sodium chloride:

• electrodes

• leads and clips

• a battery

• a beaker

• the solution of sodium chloride.

Draw a labelled diagram in the box to show how Sundip sets up her experiment to pass electricity through the solution of dilute sodium chloride.