OCR GCSE Combined Science B (21st Century) Paper 6 November 2021 question paper

The table shows data about the composition of the Earth’s atmosphere 4 billion years ago and

Complete the table to show the approximate percentage of other gases in the atmosphere

4 billion years ago.

Four billion years ago the Earth was extremely hot.

When the temperature of the Earth cooled to below 100 °C there was a large decrease in the amount of water vapour in the atmosphere.

Describe what happens when hot water vapour cools to below 100 °C.

Use ideas about arrangement and speed of particles in your answer.

How and why have the percentages of carbon dioxide and oxygen in the atmosphere changed over time?

Use data from the table to support your answer.

Some rocks are red because they contain iron oxide.

Iron oxide was formed when iron in the rocks reacted with oxygen in the atmosphere.

Complete the balanced symbol equation for the reaction which produces iron oxide.

Scientists think these red rocks formed 2.3 million years ago.

Suggest why these rocks could not form 4 billion years ago.

Use data from the table to support your answer.

Table 2.1 shows data about the sizes of some particles.

James comments on the data in Table 2.1.

Discuss James’ comment.

Use Table 2.1 to support your answer.

Table 2.2 shows information about the particles in some silver powders.

Which type of powder in Table 2.2 provides the biggest surface area for a given volume of silver?

Give one reason for your answer.

James thinks that the data in Table 2.2 gives this relationship.

Is James correct?

Explain your answer.

The different ways that nanoparticles are used depends on their properties.

Draw lines to connect each property of nanoparticles with the use that depends on it.

Nanoparticles are used as catalysts.

Which two statements explain how a catalyst increases the rate of a reaction?

Tick (✓) two boxes.

Mendeleev developed an early Periodic Table based on the elements that were known about at the time. He put these elements in order of increasing atomic mass.

Here is part of Mendeleev’s table.

Mendeleev left gaps in positions A and B in his table.

How did leaving these gaps help him to arrange the other elements into groups?

Use ideas about properties of elements in your answer.

How did the work of later scientists show that he was correct to leave gaps?

What is unusual about the positions of Te and I ?

The modern Periodic Table is organised in order of the atomic number of the elements.

Fig. 4.1 shows the arrangement of electrons in lithium and fluorine.

How does the arrangement of electrons in lithium relate to its atomic number, group and period?

Atomic number........

Group........

Period........

Lithium is a metal and fluorine is a non-metal.

Explain how and why metals and non-metals form different types of ions.

Use Fig. 4.1 to support your answer.

Sarah investigates the rate of reaction when zinc reacts with dilute sulfuric acid.

She adds small pieces of zinc to 50 cm³ of 0.1 mol / dm³ sulfuric acid. She measures the volume of hydrogen gas collected every 30 seconds.

Sarah finds that the reaction is very slow and so she increases the temperature.

Explain why increasing the temperature increases the rate of a reaction.

Use ideas about collisions of particles in your answer.

Give two other ways that she could speed up the reaction.

Sarah plots a graph from her results.

How long does it take for the reaction to finish?

What volume of hydrogen is given off by the end of the reaction?

Calculate the average volume of hydrogen given off per second.

........ cm³ / s

Draw a tangent on the graph and use it to calculate the initial rate of the reaction in cm³ / s.

Initial rate =........ cm³ / s

Some zinc pieces are left behind when the reaction ends.

Explain how and why the rate of reaction changes during the first two minutes of the reaction.

Carbon dioxide gas in the atmosphere is one cause of the greenhouse effect.

Explain how carbon dioxide causes the greenhouse effect.

Include ideas about radiation from the Sun.

Carbon dioxide gas, CO₂(g) dissolves in seawater to form dissolved carbon dioxide, CO₂(aq).

Dissolved carbon dioxide reacts with seawater to form two new ions. The two new ions are soluble.

Equation 1 shows what happens when dissolved carbon dioxide reacts with water.

Complete equation 1 by adding the missing state symbols.

Equation 1 shows an equilibrium reaction.

The pH of seawater is 7.5.

The reaction in equation 1 causes the pH of seawater to change.

Explain how and why the pH changes.

Ling does an experiment. She bubbles carbon dioxide through water.

She uses this apparatus.

Suggest two methods for showing that the pH of the water changes.

Fig. 6.1 shows the structures of diamond and methane.

Complete the dot and cross diagram for methane.

Show outer electrons only, and label each atom.

Complete the table by giving the type of bonds and type of structure for diamond and methane.

Use Fig. 6.1.

Explain why diamond is a solid and methane is a gas at room temperature and pressure.

Use ideas about bonds and attractions between molecules in your answer.

Diamond is an allotrope of carbon.

Fig. 6.2 shows the structure of graphite, another allotrope of carbon.

Graphite conducts electricity, but diamond does not.

Explain this statement.

Diamond is a very hard material, but graphite is soft and slippery.

Explain this statement.

7* Layla investigates the trend in reactivity of the Group 7 elements, using these solutions:

Describe what experiments she should do, what observations she should expect and explain how her observations can be used to show the trend in reactivity of the Group 7 elements.

Aluminium is extracted from aluminium oxide by electrolysis.

Solid aluminium oxide is dissolved in a hot, molten compound called cryolite and then electrolysed.

Explain why solid aluminium oxide cannot be electrolysed.

Use ideas about ions in your answer.

The melting point of pure aluminium oxide is 2072 °C. Aluminium oxide dissolved in cryolite melts at approximately 900 °C.

Explain one advantage of electrolysing aluminium oxide dissolved in cryolite instead of pure molten aluminium oxide.

The diagram shows the tank used for the electrolysis of aluminium oxide.

Positive electrodes dip into the molten solution of aluminium oxide.

The casing of the tank acts as the negative electrode.

Molten aluminium metal collects at the bottom.

Describe what happens at each electrode during electrolysis of aluminium oxide.

Use ideas about ions and electrons in your answer.

Copper is extracted by heating copper oxide (CuO) with carbon to form copper and carbon dioxide.

Write a balanced symbol equation for this reaction.

Explain why copper can be extracted by this method but aluminium cannot.

Bioleaching and phytoextraction are new biological methods of extracting metals from waste heaps around old mines.

Bioleaching uses bacteria on waste heaps. The waste heaps need to be first sprayed with dilute acid. The bacteria then produce a dilute solution of metal ions which can be collected.

Phytoextraction uses plants to absorb metal ions from the waste heaps and store them in their leaves. Some plants can even absorb metals which are toxic to other plants and animals.

Traditional methods of extracting metals use electrolysis or heating with carbon.

Give two advantages and one disadvantage of using biological methods of extracting metals instead of traditional methods.

Kareem does a titration to find the concentration of some dilute sulfuric acid.

He uses 25.0 cm³ of a sodium hydroxide solution with a concentration of 8.0 g / dm³ and measures the volume of sulfuric acid which reacts exactly with the sodium hydroxide solution.

The table shows Kareem’s results for the volume of acid added.

Give two errors that Kareem has made when recording his results in the table.

Why is the volume of acid added for the repeat readings less than that added in the rough trial?

Kareem decided that the most accurate value for the volume of acid added was 23.5 cm³ (iii)

Explain how he calculated this value.

Kareem’s results show that 25.0 cm³ of 8.0 g / dm³ sodium hydroxide solution are neutralised (b) by 23.5 cm³ of sulfuric acid.

The balanced symbol equation for the reaction is:

Calculate the mass of sodium hydroxide in 25.0 cm³ of the 8.0 g / dm³ solution. (i)

Show that the number of moles of sulfuric acid reacting with the sodium hydroxide is 0.0025.

Use your answer to (b)(i).

Calculate the concentration of the sulfuric acid, in mol / dm³.

Give your answer to 2 significant figures.

Concentration =........ mol / dm³