OCR GCSE Chemistry B (21st Century) Paper 3 November 2021 question paper

Chlorine is used to make water safe to drink.

How does chlorine make water safe to drink?

James has a solution of chlorine in water.

He tests the solution with blue litmus paper.

State two colour changes that James will see.

Mia adds a solution of chlorine to a solution of sodium bromide.

This is the equation for the reaction that happens:

The solution changes colour.

State the colour of the solution at the end of the experiment.

What causes the colour change?

Potassium reacts with chlorine. Sodium also reacts with chlorine.

Is the reaction of sodium with chlorine faster or slower than the reaction of potassium with chlorine?

Explain why the rate of reaction is different.

Calcium also reacts with chlorine. Calcium forms Ca²⁺ ions and chlorine forms Cl^– ions.

What is the correct formula of calcium chloride?

CaCl Ca₂Cl₂ CaCl₂ ClCa₂ ClCa

The element astatine, At, is below iodine in Group 7 of the Periodic Table.

Which two properties of astatine are correct?

Tick (✓) two boxes.

Alex measures the volume of gas made at the start and then again after every minute for 7 minutes.

Fig. 2.2 shows a graph of his results:

What is the gradient of the curve at 5 minutes?

Gradient =........ cm³ / minute

What happens to the reaction after 5 minutes?

Which value is a correct estimate for the rate at which the reaction starts?

Use Fig. 2.2.

Tick (✓) one box.

2.0 g of zinc makes a total of 800 cm³ of gas. (c)

Calculate the mass of zinc Alex used in his experiment.

Use the total volume of gas produced in Fig. 2.2.

Alex repeats the experiment with different metals and excess acid. He wants to compare the rate of reaction for the different metals.

State two factors that he should control in these experiments to get valid results.

Fig. 2.3 shows Alex’s results for zinc, magnesium and iron:

Which metal makes each curve in Fig. 2.3 ?

Curve A........

Curve B........

Curve C........

In very cold conditions, hand warmers can be used inside gloves. One type of hand warmer uses a chemical reaction to give off heat.

Iron powder inside the hand warmer reacts with oxygen to make iron oxide. An exothermic reaction starts when the iron powder comes into contact with the air.

Draw and label the reaction profile for this reaction.

Label the activation energy ‘AE’.

Carbon is used as a catalyst in the hand warmer.

Suggest why a catalyst is added to the hand warmer.

Why does the catalyst have the effect identified in (c)(i) ?

Use ideas about energy in your answer.

The iron is in powdered form.

Explain why this makes the reaction go quickly.

Use ideas about particles in your answer.

In the early nineteenth century, a chemist called Dobereiner found some sets of three elements with similar properties.

The table shows an example:

Lithium, sodium and potassium react in a similar way with water.

Balance the symbol equation for the reaction of lithium with water.

Potassium is more reactive with water than sodium and lithium.

State two observations that would prove this.

Which property is used to arrange the elements in the modern Periodic Table?

Tick (✓) one box.

Dobereiner called his sets of three elements, ‘triads’. He had this idea:

‘The relative atomic mass of the middle element is approximately equal to the mean of the other two elements.’

The elements nitrogen, phosphorus and arsenic:

• have similar properties

• are found in Group 5 of the modern Periodic Table.

Are nitrogen, phosphorus and arsenic a Dobereiner ‘triad’?

Use the Data Sheet and a calculation to help explain your answer.

Crude oil contains many compounds that are used as fuels. The table shows information about some of these compounds:

All the compounds in the table are alkanes, except benzene.

Explain how the formula of benzene shows it is not an alkane.

Name one compound from the table which is a solid at 25 °C.

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

Describe the relationship between melting point and boiling point for the alkanes in the table.

The graph shows the boiling point and relative formula mass for some alkanes.

Hexadecane, C₁₆H₃₄, boils at 287 °C. Plot the point for hexadecane on the graph.

Use data from the table.

Draw a line of best fit.

Estimate the boiling point of dodecane, C₁₂H₂₆.

Show your working on the graph.

Fractional distillation is used to separate the compounds in crude oil.

Which property of the compounds is used to separate them?

Describe how carbon monoxide forms when alkanes burn in vehicle engines.

Why is it important to decrease the amount of carbon monoxide entering the air?

The formula of carbon monoxide is CO. One mole of carbon monoxide contains 6.02 × 10²³ molecules.

Calculate the mass of one carbon monoxide molecule.

Give your answer to 3 significant figures.

Nitrogen oxides are also formed in vehicle engines.

Describe how nitrogen oxides form in vehicle engines.

Scientists use models to describe things that are too small to be seen.

Fig. 6.1 shows a model of an atom:

Name the particles represented by black circles in the model.

Identify the element in Fig. 6.1.

Use the Data Sheet.

How was the element in Fig. 6.1 identified in (b)(i) ?

Which two features are shown by the model in Fig. 6.2 ?

Tick (✓) two boxes.

State the empirical formula of butane.

Fig. 6.3 shows models of four types of giant structure.

Which two structures contain covalent bonds?

A B C D

Which structure only conducts electricity when it is molten?

A B C D

Amaya is given some coloured sweets. She removes the food colour from each sweet. Each food colour contains a mixture of dyes.

She uses chromatography to find out the number of dyes in each sweet:

• She draws a pencil line on a piece of filter paper 1 cm from the bottom.

• She puts spots of food colour from each sweet on the pencil line.

• She places the filter paper in 2 cm of water in a beaker.

• She waits for the water to rise to near the top of the filter paper.

There is a mistake in Amaya’s method.

Identify the mistake in Amaya’s method.

Why will this mistake stop Amaya from getting useful results?

Amaya says, ‘The chromatogram shows that there were a total of four different pure dyes used in the three sweets.’

Explain why this is incorrect.

Which dye is the most soluble in water?

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

Calculate the R_f value for the yellow dye.

Use the chromatogram and the equation:

Ali has a mixture of carbon in copper sulfate solution. Carbon is insoluble in water.

Describe a method Ali can use to obtain pure copper sulfate crystals from the mixture.

Plastic bags are made of poly(ethene).

Poly(ethene) is made by polymerising ethene, C₂H₄.

Draw the structure of the repeating unit of poly(ethene).

What type of polymer is poly(ethene)?

Ethene, C₂H₄, is made by cracking molecules such as decane, C₁₀H₂₂. One other product is made in the reaction.

Write a balanced symbol equation for the cracking of decane.

Ethene is an alkene.

Describe a laboratory test for an alkene and the expected result for ethene.

Test........

Result........

Table 8.1 shows the energy required to make 1000 poly(ethene) bags and transport them to shops:

Calculate the percentage of the energy in the table required to transport the bags.

Give your answer to 1 decimal place.

Sarah estimates the cost of recycling waste bags into new bags.

Table 8.2 shows her estimates:

Suggest why Sarah’s estimates may be inaccurate.

Use data from Table 8.1 and Table 8.2 to support your answer.

Poly(ethene) is described as ‘non-biodegradable’.

Define ‘ non-biodegradable ’.

Blue copper sulfate crystals turn white when heated:

• Sarah weighs out five different samples of ‘blue copper sulfate’.

• She puts each sample in a test tube.

• She heats each test tube.

• She weighs each test tube and its contents after heating.

• She then calculates the mass of ‘white copper sulfate’.

The graph shows the results:

Mass of ‘blue copper sulfate’ at start (g)

Fig. 9.1

Result A does not fit the pattern.

Sarah says the test tube was not heated for long enough.

Is Sarah correct? Explain your answer.

The equation for the line in Fig. 9.1 is given by y = m x + c.

Calculate values for m and c, using Fig. 9.1.

25 g of ‘blue copper sulfate’ gives 16 g of ‘white copper sulfate’ when heated.

Calculate the number of moles of water that are made.

‘Blue copper sulfate’ has the formula CuSO₄•nH₂O, where n is a whole number.

In one experiment, Sarah makes 2.0 mol of water and 0.4 mol of ‘white copper sulfate’.

‘White copper sulfate’ has the formula CuSO₄.

Calculate the value of n in ‘blue copper sulfate’, CuSO₄•nH₂O.