Catalysts

Hydrogen peroxide decomposes into water and oxygen.

The equation for the reaction is:

A student investigated the effect of catalyst A and of catalyst B on the rate of this reaction.

Figure 6 shows the apparatus.

This is the method used.

1. Put the conical flask on the balance.

2. Add 50 cm³ of 1.5 mol/dm³ hydrogen peroxide solution to the conical flask.

3. Add 1.00 g of catalyst A to the conical flask.

4. Start a timer.

5. Record the loss in mass of the conical flask and contents every 30 seconds for 3 minutes.

6. Repeat steps 1 to 5 using catalyst B.

Explain why the conical flask and contents lost mass.

Figure 7 shows the reaction profile for the decomposition of hydrogen peroxide using:

catalyst A

catalyst B.

Explain why catalyst A and catalyst B give different rates of reaction for the decomposition of hydrogen peroxide.

Figure 8 shows the results for catalyst A.

Determine the rate of the reaction when the time was 60 seconds.

Give your answer in standard form.

Explain how the rate of decomposition of hydrogen peroxide depends on the temperature of the solution.

This question is about ammonia.

Ammonia is produced from nitrogen and hydrogen in the Haber process.

Hydrogen is produced from methane and steam.

The equation for one of the reactions in the production of hydrogen is:

The forward reaction absorbs energy from the surroundings.

Explain why a high temperature is used in this reaction.

Explain why as low a pressure as possible is used in this reaction.

A nickel catalyst is used in this reaction.

What is the effect of the nickel catalyst on the position of equilibrium?

Tick (✓) one box.

The nitrogen needed in the Haber process is obtained from air.

Calculate the approximate volume of air required to obtain 50 dm³ of nitrogen.

Figure 9 shows how ammonia is produced from nitrogen and hydrogen.

Explain how the mixture of ammonia, nitrogen and hydrogen is separated at X.

Ammonia is used to produce fertilisers.

Nitrogen is released into the air when bacteria break down fertilisers and dead plant matter.

One of the reactions during the production of hydrogen from methane (natural gas) releases carbon dioxide into the air.

The use of nitrogen to produce ammonia is more sustainable than the use of hydrogen to produce ammonia.

Give three reasons why.

This question is about oxygen.

Scientists think that there was little or no oxygen in the Earth’s early atmosphere.

Which planet today has an atmosphere that is similar to the Earth’s early atmosphere?

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Which is the approximate percentage of oxygen in the Earth’s atmosphere today?

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Which two of the following increased the percentage of oxygen in the Earth’s atmosphere?

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Some scientists think that 1100 million years ago the Earth’s atmosphere contained:

• 16% oxygen

• 4% carbon dioxide.

Complete Figure 1.

You should:

• complete the y-axis scale

• plot the percentage of oxygen in the Earth’s atmosphere 1100 million years ago.

Oxygen is produced when manganese dioxide is added to hydrogen peroxide solution.

The equation for the reaction is:

hydrogen peroxide → water + oxygen

A student investigated the effect of changing the temperature on the decomposition of hydrogen peroxide.

This is the method used.

1. Add 5 cm³ of hydrogen peroxide solution to three test tubes labelled A, B and C.

2. Place each test tube in a water bath at a different temperature.

3. Add 0.2 g of manganese dioxide to each test tube.

Figure 2 shows the results.

Which test tube contained hydrogen peroxide solution at the highest temperature?

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The student tested the gas produced.

What is used to prove that the gas is oxygen?

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Manganese dioxide does not appear in the chemical equation for this reaction.

Which is a correct statement about manganese dioxide in this reaction?

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Manganese dioxide catalyses the decomposition of hydrogen peroxide solution. Oxygen and water are produced.

Explain how a manganese dioxide catalyst increases the rate of decomposition of hydrogen peroxide.

A student investigated the rate of this reaction. This is the method used.

1. Add 50 cm³ of 2.0 mol/dm³ hydrogen peroxide solution to a conical flask.

2. Add 1.0 g of manganese dioxide to the conical flask.

3. Place the conical flask on a balance and start a timer.

4. Record the total mass lost from the conical flask every 20 seconds for 180 seconds.

Explain why the mass of the conical flask and contents decreased.

Figure 4 shows the results for 50 cm³ of 2.0 mol/dm³ hydrogen peroxide solution and 1.0 g of manganese dioxide. A tangent to the line has been drawn at 75 seconds.

Determine the rate of reaction when the time was 75 seconds. Give your answer to 2 significant figures.

The results for 50 cm³ of 2.0 mol/dm³ hydrogen peroxide solution and 1.0 g of manganese dioxide are shown again on Figure 5.

The student repeated the investigation using 50 cm³ of 1.0 mol/dm³ hydrogen peroxide solution and 1.0 g of manganese dioxide. Sketch the expected results for 1.0 mol/dm³ hydrogen peroxide solution on Figure 5.

This question is about ammonia and fertilisers.

Ammonia is produced from nitrogen and hydrogen.

A catalyst is used to speed up the reaction.

The word equation for the reaction is:

nitrogen + hydrogen ammonia

What does the symbol show about the reaction?

Which catalyst is used when ammonia is produced from nitrogen and hydrogen?

Tick (✓) one box.

Figure 1 shows the reaction profile for the production of ammonia both with a catalyst and without a catalyst.

What is represented by label X ?

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Ammonia is used to produce fertilisers.

NPK fertilisers contain the elements nitrogen, phosphorus and potassium.

A fertiliser contains:

• 22% phosphorus

• 25% potassium.

Draw a bar chart on Figure 2 to show the percentages of phosphorus and of potassium in this fertiliser.

Why do the percentages of phosphorus and of potassium in this fertiliser not add up to 100%?

Fertilisers help plants grow by adding essential elements to soil.

Table 1 shows the percentages of nitrogen, phosphorus and potassium in four fertilisers, A, B, C and D.

Plants lacking essential elements do not grow well because:

• too little phosphorus can cause slow plant growth

• too little potassium can cause leaves to have brown edges.

Which fertiliser helps prevent slow plant growth and brown leaf edges?

Use Table 1.

Tick (✓) one box.

Which fertiliser has the greatest total percentage of essential elements?

Use Table 1.

Tick (✓) one box.

Hydrogen is a raw material in the Haber process.

Hydrogen is produced from methane.

The word equation for the reaction is:

methane + steam carbon monoxide + hydrogen

How can you tell that the reaction is reversible?

The forward reaction is endothermic.

Name the type of energy change in the reverse reaction.

A nickel catalyst is used in this reaction.

Why is a catalyst used in this reaction?

Tick (✓) two boxes.

The Haber process also uses nitrogen to produce ammonia.

Figure 1 shows how the world production of ammonia changed between 1950 and 2010.

Describe how the world production of ammonia changed between 1950 and 2010.

Most of the ammonia produced is used to make fertilisers.

Why did the world production of ammonia change between 1950 and 2010?

Tick (✓) two boxes.

Table 1 shows data about four fertilisers, A, B, C and D.

Which combination of fertilisers A, B, C and D provides all of the elements needed for an NPK fertiliser?

Use Table 1.

Tick (✓) one box.

Which fertiliser is not made using ammonia?

Use Table 1.

Tick (✓) one box.

Some students investigated the rate of decomposition of hydrogen peroxide.

The equation for the reaction is:

hydrogen peroxide → water + oxygen

Complete the sentence.

Choose an answer from the box.

The students tested the gas produced to show that it was oxygen.

The students used.

Student A investigated the effect of the particle size of a manganese dioxide catalyst on the rate of the reaction.

This is the method used.

1. Measure 25 cm³ hydrogen peroxide solution into a conical flask.

2. Add some fine manganese dioxide powder to the conical flask.

3. Measure the volume of oxygen produced every 30 seconds for 10 minutes.

4. Repeat steps 1 to 3 two more times.

5. Repeat steps 1 to 4 with coarse manganese dioxide lumps.

The method student A used did not give repeatable results.

How could student A make the results repeatable?

Tick (✓) one box.

Student B used a method which gave repeatable results.

How could student B improve the accuracy of these results?

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Figure 5 shows student B ’s results for coarse manganese dioxide lumps.

Calculate the mean rate of reaction between 30 and 250 seconds for coarse manganese dioxide lumps.

Use Figure 5 and the equation:

Give your answer to 3 significant figures.

Volume of oxygen formed

Mean rate of reaction = cm³/s

Fine manganese dioxide powder produces a higher rate of reaction than coarse manganese dioxide lumps.

Sketch on Figure 5 the results you would expect for student B ’s experiment with fine manganese dioxide powder.

Hydrogen peroxide molecules collide with manganese dioxide particles during the reaction.

Why does fine manganese dioxide powder produce a higher rate of reaction than coarse manganese dioxide lumps?

Tick (✓) one box.

This question is about methanol.

Methanol is broken down in the body during digestion. What type of substance acts as a catalyst in this process?

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In industry, methanol is produced by reacting carbon monoxide with hydrogen. The equation for the reaction is:

How many moles of carbon monoxide react completely with 4.0 10³ moles of hydrogen?

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The reaction is carried out at a temperature of 250 ºC and a pressure of 100 atmospheres. The forward reaction is exothermic. Explain what happens to the yield of methanol if a temperature higher than 250 ºC is used.

A pressure of 100 atmospheres is used instead of atmospheric pressure. The higher pressure gives a greater yield of methanol and an increased rate of reaction. Explain why.

A catalyst is used in the reaction to produce methanol from carbon monoxide and hydrogen.

Explain how a catalyst increases the rate of a reaction.

Suggest why a catalyst is used in this industrial process. Do not give answers in terms of increasing the rate of reaction.

Suggest the effect of using the catalyst on the equilibrium yield of methanol.