OCR GCSE Combined Science B (21st Century) Paper 6 June 2019 question paper

Alkanes are a family of hydrocarbons in crude oil. They all have the same general formula, C_nH_2n+2.

Table 1.1 shows some information about alkanes.

Complete the blank spaces in Table 1.1 to show the missing formulae.

Which statements about a structural formula are true and which are false ?

Tick (✓) one box in each row.

Predict the boiling point of hexane.

Use the data in Table 1.1 to help you.

Explain why it is difficult to use the data in Table 1.1 to predict the melting point butane.

What is the state of pentane at 25 °C?

Explain your answer.

State:........

Explanation:........

Explain the trend in boiling points in Table 1.1.

Use ideas about energy and intermolecular forces in your answer.

Carbon nanotubes were discovered in 1991.

Materials made from nanotubes can be used instead of steel because nanotubes are very strong. They are a few nanometres wide and up to 1 cm long.

The structure of a nanotube is shown below.

Nanotubes are nanoparticles.

Which statement explains why nanotubes are nanoparticles?

Tick (✓) one box.

Which two statements explain why nanotubes are very strong?

Tick (✓) two boxes.

Nanotubes are a similar shape to a human hair but they are much smaller.

A human hair has a diameter of 0.001 mm. A nanotube has a diameter of 2 nm and a length of 5 mm.

A scale model of a nanotube has the same diameter as a human hair.

What is the length of the scale model in mm?

1 nm = 1 × 10^–6 mm

Short nanotubes can also be used to carry medicines into the body.

The medicine is put inside the tube and the tube is injected into the body.

Give one benefit and one risk of using nanotubes to carry medicines into the body.

Benefit

Risk

James investigates the effect of concentration of acid on the rate of reaction, using dilute hydrochloric acid and sodium thiosulfate solution.

He stands a conical flask on a piece of paper marked with a cross.

He adds the reactants to the flask and immediately starts a stop watch.

He looks at the cross from above and stops timing when the cross becomes hidden by the contents of the flask.

This is the equation for the reaction.

Explain why the cross becomes hidden by the contents of the flask.

Suggest a piece of apparatus that James could use to accurately measure out the dilute acid, water and sodium thiosulfate.

Explain why different volumes of water are used for each experiment.

Describe and explain the effect of changing the concentration of hydrochloric acid on the rate of reaction.

Use ideas from the particle model in your answer.

Many countries with sunny climates get most of the salt they need from seawater.

The seawater is trapped in shallow pools and left in the sun. After some time, piles of solid salt can be collected.

Why does this method work well in countries with warm climates?

Piles of solid salt contain insoluble impurities such as sand.

Jack collects a sample of solid salt.

Describe an experiment that Jack could do to find out an accurate value for the mass of pure salt in his sample.

Here are the results of one experiment.

Mass of salt mixed with sand = 5.42 g

Mass of pure salt obtained = 1.36 g

Calculate the percentage of pure salt in the sample.

Give your answer to 3 significant figures.

Lithium is one of the elements in Group 1 of the Periodic Table. Lithium atoms have the electron arrangement 2.1.

Give one similarity and one difference in the way that the electron arrangement of Lithium is the same as the electron arrangements of other atoms in Group 1 of the Periodic Table.

Similarity:........

Difference:........

Explain why elements on the left of the Periodic Table are metals.

Name the two products of the reaction between lithium and water.

What two changes will Beth see when these products form?

Beth repeats her experiment with sodium and then potassium. She uses fresh water and indicator each time.

How will the observations from her experiments show the trend in reactivity of the Group 1 metals?

* The table shows the emissions of nitrogen oxides and carbon monoxide from 1980 to 2015 for cars in the UK.

Catalytic converters have been fitted to all new cars since 1993.

Using the data in the table, discuss how and why the emissions from cars has changed from 1980 to 2015.

Your answer should include descriptions of the reactions that produce the emissions, including those that occur in the catalytic converter.

Car emissions also contain small amounts of sulfur dioxide.

The amount of sulfur dioxide emitted by cars in 2019 is much less than it was 20 years ago.

Which two statements about sulfur dioxide emissions from cars are true?

Tick (✓) two boxes.

Hydrogen peroxide (H₂O₂) is made in the body.

An enzyme breaks down the hydrogen peroxide into water and oxygen before it can damage cells in the body.

Write a balanced symbol equation for the breakdown of hydrogen peroxide into water and oxygen.

Ben investigates how this enzyme affects the rate of breakdown of hydrogen peroxide at different temperatures.

He uses a solid enzyme and a solution of hydrogen peroxide.

Give two variables which Ben must keep constant at each temperature.

When Ben does a trial experiment he finds that the reaction is very slow.

What changes can he make for the reaction to be faster at each temperature?

Ben uses his results to plot a graph of the rate of reaction against temperature, as shown in Fig. 7.1.

Explain why, initially, the rate of reaction increases as the temperature increases.

Use ideas from the particle model in your answer.

Describe how the rate of reaction changes at temperatures above 30 °C.

Explain your answer.

What is the optimum temperature for the reaction shown in Fig. 7.1 ?

Zinc metal is extracted from zinc blende (ZnS). The zinc blende is roasted in oxygen to form zinc oxide and sulfur dioxide.

The zinc oxide is then heated with carbon at high temperature to form zinc and carbon dioxide. The zinc gas is cooled in an inert atmosphere to form solid zinc.

Explain what has happened to the zinc oxide in this reaction.

Why is zinc gas cooled in an inert atmosphere rather than in air?

What is the maximum mass of zinc that can be extracted from 10 tonnes of zinc oxide?

Mass of zinc =........ tonnes

Carbon cannot be used to extract aluminium from aluminium oxide.

What method is used to extract aluminium?

Explain why carbon can be used to extract zinc but not aluminium.

There are piles of waste rock left near to old zinc mines. The rock contains lead impurities. Lead is toxic and may get into streams and rivers.

A new method called phytoextraction uses plants to remove the lead impurities from the piles of waste rock.

Describe how plants can be used to completely remove the lead impurities from the piles of waste rock near old zinc mines.

Charcoal used on a barbecue is a form of carbon.

When charcoal burns in plenty of air it forms carbon dioxide. The reaction is exothermic.

David uses a burning firelighter to make some of the charcoal start to burn.

When the firelighter has been used up, the fire continues to spread until all the charcoal is burning.

Explain why the charcoal will not start to burn without using the firelighter and why the fire spreads after the firelighter is used up.

Complete the reaction profile diagram for the combustion of charcoal.

Include the following labels on your diagram:

reactants products activation energy energy change of reaction

When charcoal burns in insufficient air it forms carbon monoxide.

Carbon monoxide can also act as a fuel.

Calculate the energy given out when 1 mole of carbon monoxide burns in air.

Use the table of bond energies.

Give your answer to 3 significant figures.

The table below gives the properties of four substances.

Which substance is a liquid over the biggest temperature range?

What type of bonding does each substance have?

Tick (✓) one box in each row.

Metals and ionic compounds conduct electricity differently.

State and explain these differences.