OCR GCSE Chemistry B (21st Century) Paper 3 November 2020 question paper

Layla does a titration to find out the concentration of some sodium hydroxide solution. She reacts hydrochloric acid with the sodium hydroxide solution.

Layla says, ‘The titration uses a neutralisation reaction.’

Define a neutralisation reaction.

This is Layla’s incomplete method for the titration:

• Put the hydrochloric acid in a burette.

• Put the sodium hydroxide solution in a flask.

• Add the hydrochloric acid to the sodium hydroxide solution.

• Stop adding the hydrochloric acid when the sodium hydroxide solution is neutralised.

Layla needs to add another substance to the flask so that she knows when to stop adding the hydrochloric acid.

Which substance does Layla need to add, and what will she see?

Layla needs to add........

Layla will see........

Layla titrates the hydrochloric acid into a flask from a burette. She wants to make sure her final burette reading is as accurate as possible.

Describe one thing Layla can do to make her reading as accurate as possible.

Layla’s results for her rough titration are shown in Table 1.1.

Complete Table 1.1 by calculating the volume for the rough titration.

Layla’s repeat readings for her careful titrations are shown in Table 1.2.

Layla calculates that the mean titration volume is 24.60 cm³.

Explain why Layla is correct.

Use the information in Table 1.2 and a calculation in your answer.

Beth has some tablets that react by fizzing, and then dissolving, when water is added.

Beth puts a whole tablet into Tube A, and a broken-up tablet into Tube B.

Whole tablet
Broken-up tablet

Fig. 2.1

Beth wants to measure the rate of the two reactions. This is Beth’s method:

• Add the same volume of cold water to each test tube at the same time.

• Start a stopwatch.

When should Beth stop the stopwatch?

Tick (✓) one box.

Which type of tablet, whole or broken-up, will dissolve more quickly?

Explain your answer.

Use ideas from the particle model in your answer.

Suggest one reason why the reactions are much faster using hot water.

Fig. 2.2 shows how the mass of Tube A and its contents changes over time when cold water is added.

Using Fig. 2.2, explain why the mass of Tube A and its contents decreases during the reaction.

The rate of the reaction decreases with time.

Describe how Fig. 2.2 shows this.

Explain why the rate of reaction decreases with time.

Ethene has some reactions that are different from those of ethane. These reactions are caused by its functional group.

1 mole of ethene contains 6.0 × 10²³ molecules. (b)

How many hydrogen atoms are there in one mole of ethene?

1 4 6 6.0 × 10²³ 2.4 × 10²⁴

Ethene (Fig. 3.1) reacts with Substance D to give the compound shown in Fig. 3.2.

Name Substance D.

Ethene also reacts with hydrogen.

Draw the displayed formula of the compound formed.

Fig. 4.1 shows how the average world temperature has changed since 1880.

Using Fig. 4.1, describe how the average world temperature changed from 1910–1930.

Between which two years was there the largest continuous temperature rise?

Some scientists believe that average world temperatures have increased due to increased amounts of greenhouse gases in the air.

Carbon dioxide is a greenhouse gas.

Amaya says,

Explain what is incorrect about Amaya's statement.

State one suitable way in which we can lower our carbon dioxide emissions.

State one effect of increasing average world temperatures on the Earth’s climate.

Amir is given a solution of potassium sulfate, which can be used as a fertiliser.

He carries out a flame test on the solution.

Describe how Amir does the flame test.

What colour does Amir see when he carries out the flame test on potassium sulfate?

Write a balanced symbol equation for the reaction of potassium sulfate (K₂SO₄) solution with barium chloride (BaCl₂) solution.

Show state symbols.

Amir has a sample of another fertiliser, Fertiliser E.

He looks at the emission spectra of Fertiliser E and potassium sulfate:

What can Amir conclude about Fertiliser E from these emission spectra?

Compounds can be analysed using a flame test or an emission spectrum.

State one advantage of using an emission spectrum to analyse compounds.

Jane and Ben discuss the investigation:

Do you agree with each person's comments?

Give one reason for each of your answers.

Jane........

Ben........

When iron rusts, an iron(III) cation is made.

What is being oxidised in this reaction?

Fe Fe³⁺ 3e^–

Give one reason for your answer to (b)(i).

Jane collects the rust. She dissolves the rust in hydrochloric acid and adds some sodium hydroxide solution.

She sees a brown precipitate.

What is the name of this brown precipitate?

Tick (✓) one box.

Drinking cups can be made from poly(propene) or aluminium.

Poly(propene) is made from propene.

The displayed formula for propene is shown below:

What is the empirical formula of propene?

Draw the structure for a repeating unit of poly(propene).

Aluminium melts at 660 °C. Poly(propene) melts at 130 °C.

Hot water from a kettle has a temperature of between 90 °C and 100 °C.

James says,

Do you agree with James?

Explain your answer.

Which statements about polymers are true, and which are false ?

Tick (✓) one box in each row.

Diamond and graphite are allotropes of carbon.

Models of diamond and graphite are shown in Fig. 8.1:

Diamond Graphite

Fig. 8.1

Graphite can mark paper but diamond cannot.

Explain why.

Use ideas about intermolecular forces and bonding in your answer.

Fig. 8.2 shows a model of sodium chloride:

What type of structure does sodium chloride have?

You should include the type of bonding in your answer.

Complete the table to explain how graphite and sodium chloride conduct electricity.

Ammonia is used to make synthetic fertilisers.

Ammonia is made by the Haber process.

The reaction in the Haber process reaches equilibrium.

Describe the rates of the forward and reverse reactions at equilibrium.

The graph shows the effect of temperature and pressure on the yield of ammonia in the Haber process:

State the lowest temperature and pressure necessary to get a yield of ammonia of 15%.

Suggest one disadvantage of using a temperature of 350 °C rather than 450 °C in the Haber process.

Sarah makes ammonium sulfate from ammonia in a laboratory. This is her method:

• Add excess ammonia to dilute sulfuric acid in an evaporating basin.

• Boil the solution until it does not smell of ammonia.

• Cool the basin until crystals form in the solution.

The crystals that form in the solution are impure.

Describe what Sarah can do to get pure ammonium sulfate crystals.

Ammonium sulfate can be mixed with other substances to make compound fertilisers.

Suggest why compound fertilisers are better for farmers than pure ammonium sulfate.

Lithium-ion batteries are used in phones, tablets and electric cars.

Lithium reacts with chlorine to form lithium chloride.

What mass of chlorine reacts with 1 g of lithium?

Give your answer to 1 decimal place.

Lithium reacts with water to form lithium hydroxide (LiOH) and a gas.

Write a balanced symbol equation for this reaction.

Lithium is made by the electrolysis of molten lithium chloride.

Name the product formed at each electrode.

Cathode........

Anode........

Nina does some experiments with chlorine.

Nina wants to use a displacement reaction to show chlorine is more reactive than bromine.

Describe what Nina needs to do and what she will see.

Nina needs to........

Nina will see........

Nina has to be careful when using chlorine in her experiments.

State one precaution she must take and why the precaution is needed.

Precaution

Why the precaution is needed

Titanium is used for hip replacements.

Titanium’s strength comes from its metallic structure as shown in Fig. 11.1.

Use Fig. 11.1 to explain why the metallic bonds in titanium are very strong.

Titanium is a transition metal. Calcium is not a transition metal.

Which two statements are correct about both calcium and titanium?

Tick (✓) two boxes.

Titanium can be made from titanium oxide by two methods.

The atom economies of the two methods can be compared using this equation:

What does atom economy tell us about a reaction?

Calculate the atom economy of Method 2.

Give your answer to 2 significant figures.

Explain, without further calculation, which method has the higher atom economy.

Jamal and Mia discuss atom economy.

Evaluate Jamal and Mia’s comments.

Magnesium oxide (MgO) is formed in Method 1.

Complete to show the ‘dot and cross’ diagrams for an Mg²⁺ ion and an O^2– ion. Fig. 11.2

Show all the electrons.