Tests for gases

A student investigated the reaction of calcium carbonate with hydrochloric acid.

Figure 2 shows the apparatus.

This is the method used.

1. Measure 50 cm³ of hydrochloric acid into a conical flask.

2. Add 4.0 g of calcium carbonate to the conical flask.

3. Insert the stopper into the conical flask as quickly as possible.

4. Start a timer.

5. Measure the volume of gas collected every 30 seconds for 3 minutes.

6. Repeat steps 1 to 5 using different concentrations of hydrochloric acid.

Name a suitable piece of equipment to measure 4.0 g of calcium carbonate.

Figure 3 shows the gas syringe during the investigation.

What is the reading on the gas syringe?

What is the independent variable in the investigation?

Tick () one box.

Why did the student insert the stopper into the conical flask as quickly as possible in step 3?

The gas produced during the investigation is carbon dioxide.

The test for carbon dioxide uses limewater.

What is the chemical name for limewater?

Tick () one box.

The student measured the volume of gas collected every 30 seconds for 3 minutes.

The volume of gas was zero at the start.

For one concentration of hydrochloric acid, the volumes of gas collected were:

Complete Table 3.

You should:

• add headings to each column

• add units

• add all of the results to the table.

The student used a different concentration of hydrochloric acid.

18 cm³ of gas was collected in the first 30 seconds.

Calculate the mean rate of reaction for the first 30 seconds.

Use the equation:

Choose the unit from the box.

Increasing the concentration of hydrochloric acid increases the rate of the reaction.

What are two reasons why?

Tick () two boxes.

Screenwash is a mixture designed to keep car windscreens clean.

The components in screenwash include glycerol, methanol and water.

Screenwash is made by mixing the components in carefully measured quantities so that the product has the required properties.

What name is given to this type of mixture?

Tick () one box.

Glycerol has the formula C₃H₈O₃

How many atoms are there in one molecule of glycerol?

Tick () one box.

Incomplete combustion happens when glycerol burns in limited oxygen.

Incomplete combustion produces carbon monoxide gas.

Why can the production of carbon monoxide gas be a problem?

Tick () one box.

Complete combustion happens when methanol (CH₄O) burns in excess oxygen.

Balance the equation for the reaction.

Methanol can be produced by the reaction of carbon dioxide with hydrogen.

Describe the test for hydrogen gas.

Give the result of the test.

Carbon dioxide is a greenhouse gas.

An increase in greenhouse gases in the atmosphere has led to an increase in average global temperature.

The increase in average global temperature has caused global climate change.

Give two effects of global climate change.

Anhydrous cobalt chloride can be used to test for water.

The word equation for the reaction is:

anhydrous cobalt chloride + water hydrated cobalt chloride (blue) (pink)

Suggest one observation that could be made when water is added to anhydrous cobalt chloride.

The reaction between anhydrous cobalt chloride and water is exothermic.

What type of reaction is the reverse reaction?

The proportions of most gases in the Earth’s atmosphere have not changed much for the past 200 million years.

About one-fifth of the atmosphere is oxygen.

Describe the test for oxygen gas.

Give the result of the test.

Table 5 shows the percentages of some gases in the Earth’s early atmosphere and in the Earth’s atmosphere today.

Explain how the percentages of gases have changed from Earth’s early atmosphere to Earth’s atmosphere today.

You should refer to all three gases in Table 5.

Methane is a greenhouse gas.

Give two ways to reduce methane emissions into the atmosphere.

The percentage of sulfur dioxide in the Earth’s atmosphere increased between 1850 and 1980.

Describe how sulfur dioxide emissions are produced.

Give one harmful effect of sulfur dioxide emissions.

Suggest one reason why the percentage of sulfur dioxide in the Earth’s atmosphere has decreased since 1980.

The proportions of most gases in the Earth’s atmosphere have not changed much for the past 200 million years.

About one-fifth of the atmosphere is oxygen.

Describe the test for oxygen gas.

Give the result of the test.

Table 1 shows the percentages of some gases in the Earth’s early atmosphere and in the Earth’s atmosphere today.

Explain how the percentages of gases have changed from Earth’s early atmosphere to Earth’s atmosphere today.

You should refer to all three gases in Table 1.

Methane is a greenhouse gas.

Give two ways to reduce methane emissions into the atmosphere.

The percentage of sulfur dioxide in the Earth’s atmosphere increased between 1850 and 1980.

Describe how sulfur dioxide emissions are produced.

Give one harmful effect of sulfur dioxide emissions.

Suggest one reason why the percentage of sulfur dioxide in the Earth’s atmosphere has decreased since 1980.

Students investigated the effect of changing the concentration on the rate of chemical reactions.

A student reacted sodium thiosulfate solution with hydrochloric acid.

Figure 3 shows the apparatus.

This is the method used.

1. Measure 50 cm³ of sodium thiosulfate solution into a conical flask.

2. Put the conical flask on a black cross drawn on a piece of paper.

3. Add 10 cm³ of hydrochloric acid to the conical flask.

4. Start a timer.

5. Stop the timer when the cross is no longer visible.

6. Record the time taken.

7. Repeat steps 1 to 6 using different concentrations of sodium thiosulfate solution.

What is the dependent variable in this investigation?

The equation for the reaction is:

Na₂S₂O₃(aq) + 2 HCl(aq) → 2 NaCl(aq) + S(s) + SO₂(g) + H₂O(l)

The mixture becomes cloudy as the reaction takes place.

Explain why the mixture becomes cloudy.

Explain the effect of changing the concentration of the sodium thiosulfate solution on the rate of reaction.

A different student reacted magnesium with hydrochloric acid.

Figure 4 shows the apparatus.

This is the method used.

1. Measure 50 cm³ of hydrochloric acid into a conical flask.

2. Add 0.1 g of magnesium ribbon to the conical flask.

3. Insert the stopper into the conical flask as quickly as possible.

4. Start a timer.

5. Record the volume of gas collected every 20 seconds for 5 minutes.

6. Repeat steps 1 to 5 using different concentrations of hydrochloric acid.

Why is the stopper inserted into the conical flask as quickly as possible in step 3?

The equation for the reaction of magnesium with hydrochloric acid is:

Describe a test for the gas produced in the reaction.

Give the result of the test.

Figure 5 shows the results for one concentration of hydrochloric acid.

Determine the rate of reaction at 75 seconds.

Different tests can be used to identify chemicals.

A student measured the melting points of four substances.

Table 1 shows the results.

Which substance was pure?

Give one reason for your answer.

Anhydrous copper sulfate can be used to test for water.

The word equation for the reaction is:

anhydrous copper sulfate + water hydrated copper sulfate

Complete the sentence.

Choose answers from the box.

When water is added to anhydrous copper sulfate, the colour changes

The reaction between anhydrous copper sulfate and water is reversible.

How does the word equation show that the reaction is reversible?

The formula of anhydrous copper sulfate is CuSO₄

What is the total number of atoms in the formula CuSO₄?

Tick () one box.

Chlorine is a gas.

Describe the test for chlorine.

Give the result.

Crude oil contains a large number of hydrocarbons.

Crude oil is a finite resource. What is a finite resource? Tick (✓) one box.

What is crude oil formed from? Tick (✓) one box.

What type of substance is crude oil? Tick (✓) one box.

The hydrocarbons in crude oil are separated into fractions using fractional distillation. Complete the sentences. Choose answers from the box.

In fractional distillation the crude oil is heated so

Hydrocarbons can be cracked to produce more useful molecules.

Complete the sentence. Choose the answer from the box.

Hydrogen gas is a product of cracking. What is used in the test for hydrogen gas? Tick (✓) one box.

5.20 kg of crude oil contains 1.53 kg of LPG (Liquefied Petroleum Gas). Calculate the percentage (%) of LPG in 5.20 kg of crude oil. Give your answer to 3 significant figures.

Some types of water contain dissolved substances.

A student investigated the mass of dissolved solids in distilled water and in sea water. Figure 5 shows the apparatus.

This is the method used.

1. Weigh an evaporating basin.

2. Add a sample of distilled water to the evaporating basin.

3. Weigh the evaporating basin and the water sample.

4. Heat the water sample.

5. Weigh the evaporating basin and contents.

6. Repeat steps 1 to 5 two more times.

7. Repeat steps 1 to 6 with sea water.

Give one safety precaution the student should take.

The method used did not give valid results. Which two improvements could the student make to give valid results? Tick (✓) two boxes.

A different student used a method which gave valid results. Table 2 shows the results.

The student concludes that distilled water is pure. Suggest one reason why.

Tap water is potable. One step in producing potable water is sterilisation.

Why is potable water sterilised?

Tick (✓) one box.

Chlorine is used to sterilise water. The reaction between chlorine and water is reversible. Complete the sentence.

Equilibrium is reached when the forward and reverse reactions

The test for chlorine uses damp litmus paper. Complete the sentence. Choose the answer from the box.

When damp litmus paper is put into chlorine gas

There is evidence that adding fluoride ions to drinking water reduces tooth decay.

Figure 6 shows the percentage of people showing tooth decay.

Compare the effects of adding fluoride ions to drinking water on tooth decay in people between the ages of 25 and 74. Use data from Figure 6.

Student A says that water companies should add fluoride ions to all drinking water. Student B disagrees. Suggest one reason why Student B may think that fluoride ions should not be added to all drinking water.

Crude oil is a mixture of many different compounds.

Give two reasons why crude oil is not a formulation.

Describe how crude oil is separated into fractions.

The fractions from crude oil contain alkanes. Explain why alkanes are cracked.

Cracking produces a mixture of products.

An equation for cracking decane (C₁₀H₂₂) is:

Describe a test to identify the gas produced in the reaction.

Alkenes are produced in cracking. The general formula for the homologous series of alkenes is C_nH_2n Which formula represents an alkene? Tick (✓) one box.

Some types of water contain dissolved substances.

A student investigated the mass of dissolved solids in distilled water and in sea water. Figure 1 shows the apparatus.

This is the method used.

1. Weigh an evaporating basin.

2. Add 20 cm³ of distilled water to the evaporating basin.

3. Weigh the evaporating basin and the water sample.

4. Heat the water sample for 2 minutes.

5. Weigh the evaporating basin and contents.

6. Repeat steps 1 to 5 two more times.

7. Repeat steps 1 to 6 with sea water.

The method used by the student did not give valid results. Describe one improvement the student could make to obtain valid results.

A different student used a method which gave valid results.

Table 2 shows the results.

Calculate the value X for the mass of dissolved solids in sea water in Test 2.

The student concludes that distilled water is pure. Describe a test to confirm that distilled water is pure.

Tap water is potable.

A stage in the production of potable water is sterilising. A gas is used to sterilise water. The equation for the reaction is:

What is meant by the symbol ?

The reaction is at equilibrium. The reaction is exothermic. What happens to the equilibrium position when the temperature is increased? Tick (✓) one box.

Describe a test to identify the gas used to sterilise water.

Another stage in the production of potable water is filtering. Explain why potable water contains dissolved solids after filtering.

A student investigated the rate of decomposition of hydrogen peroxide using three different catalysts:

• manganese dioxide

• copper oxide

• zinc oxide.

Figure 2 shows the apparatus.

This is the method used.

1. Measure 20 cm³ of hydrogen peroxide solution into a flask.

2. Add 0.5 g of manganese dioxide catalyst to the flask.

3. Attach a gas syringe to the flask.

4. Measure the volume of oxygen produced every 30 seconds for 180 seconds.

5. Repeat steps 1 to 4 two more times.

6. Repeat steps 1 to 5 using copper oxide catalyst.

7. Repeat steps 1 to 5 using zinc oxide catalyst.

The equation for the decomposition of hydrogen peroxide is:

Describe a test to identify the gas produced in the reaction.

Using 10 cm³ of hydrogen peroxide solution gives less accurate results than using 20 cm³ of hydrogen peroxide solution of the same concentration. Explain why.

Suggest one possible source of systematic error in the investigation.

Table 3 shows the results for manganese dioxide catalyst.

Figure 3 shows a graph of the results with copper oxide catalyst and with zinc oxide catalyst.

Complete Figure 3. You should:

• plot the data from Table 3

• draw a line of best fit.

The first point has been plotted for you.

Which catalyst gives the fastest rate of reaction? Give one reason for your answer. Use the completed Figure 3.

The rate of reaction is not dependent on the volume of hydrogen peroxide solution. Explain why.

Figure 4 shows the results from a different investigation.

Determine the rate of reaction at 20 seconds. Show your working on Figure 4. Give your answer to 3 significant figures.

This question is about the Earth’s atmosphere.

What is used to test for oxygen gas?

Tick (✓) one box.

The Earth’s early atmosphere was very different from the Earth’s atmosphere today.

Figure 2 shows the composition of the Earth’s early atmosphere and of the Earth’s atmosphere today.

The Earth’s atmosphere today contains a small amount of carbon dioxide.

Why has the percentage of carbon dioxide decreased since the Earth’s early atmosphere?

Tick (✓) two boxes.

Oxides of nitrogen are produced when nitrogen reacts with oxygen in car engines.

Figure 3 shows the concentration of oxides of nitrogen in the atmosphere during one day in a city.

Which two times have the highest concentrations of oxides of nitrogen in the atmosphere?

Suggest why there are the highest concentrations of oxides of nitrogen at these times.

Cars cause atmospheric pollution.

Figure 2 shows the percentage of cars in the UK using different energy sources.

The percentage of cars using petrol is 54%. Draw the bar for petrol on Figure 2.

Some car emissions contain nitrogen dioxide.

Table 1 shows the concentration of nitrogen dioxide in the air in three different areas for 1 week.

Which column of data has the greatest range? Tick (✓) one box.

Explain why the concentration of nitrogen dioxide in the air is lower on Sunday.

Calculate the mean value for the concentration of nitrogen dioxide in the air in the city centre for the days from Monday to Friday. Use Table 1.

Nitrogen dioxide is removed from car emissions by catalytic converters.

Which two of the following are correct statements about catalysts? Tick (✓) two boxes.

The catalyst in catalytic converters contains platinum. Platinum is an unreactive metal obtained from the Earth’s crust. Complete the sentence. Choose the answer from the box.

Platinum is a.

Emissions from cars that burn fossil fuels contain carbon dioxide. What is used to test for carbon dioxide? Tick (✓) one box.

Ammonia is produced when a mixture of nitrogen and hydrogen reacts.

The equation for the reaction is:

Nitrogen is obtained from the air.

The mixture of nitrogen and hydrogen must not contain carbon dioxide and oxygen.

Explain how a sample can be tested to show that carbon dioxide is not present in the mixture.

A catalyst is used in the reaction.

Explain how a catalyst increases the rate of a reaction.

The equation for the reaction to produce ammonia is repeated here.

The reaction reaches equilibrium.

Explain how an equilibrium is reached.

Suggest how the catalyst affects the equilibrium position.

Give one reason for your answer.

What is the effect of increasing the pressure on the reaction to produce ammonia?

Tick (✓) one box.

The forward reaction is exothermic.

Explain the effect of increasing the temperature on the yield of ammonia gas produced at equilibrium.

This question is about the Earth’s resources.

When most fuels burn carbon dioxide is produced.

Balance the equation for the combustion of propane.

Describe the test for carbon dioxide. Give the result of the test.

Propane can be cracked to produce propene and hydrogen. Complete the symbol equation for the reaction.

Describe the test for hydrogen. Give the result of the test.

Propene is an alkene. Describe the test for alkenes. Give the colour change in the test.

This question is about the Earth’s resources.

When most fuels burn carbon dioxide is produced.

Balance the equation for the combustion of propane.

Describe the test for carbon dioxide. Give the result of the test.

Propane can be cracked to produce propene and hydrogen. Complete the symbol equation for the reaction.

Describe the test for hydrogen. Give the result of the test.

Propene is an alkene. Describe the test for alkenes. Give the colour change in the test.

This question is about gases.

Draw one line from each substance to the description of the substance.

What is used to test for each of the gases?

Draw one line from each gas to the test for the gas.

Give two reasons why the percentage of carbon dioxide in the air has decreased in the last 2.7 billion years.

Tick (✓) two boxes.

Oxygen reacts with sulfur dioxide.

The reaction is reversible.

What is the symbol for a reversible reaction?

Complete the sentence.

In a reversible reaction the forward reaction is exothermic, so the

A reversible reaction happens in apparatus which stops the escape of reactants and products.

Complete the sentence.

Equilibrium is reached when the forward and reverse reactions happen at

This question is about oxygen (O₂) and sulfur dioxide (SO₂).

Give the test and result for oxygen gas.

The reaction between oxygen and sulfur dioxide is at equilibrium.

Some of the sulfur trioxide (SO₃) is removed. Explain what happens to the position of the equilibrium.

Sulfur dioxide is an atmospheric pollutant. Sulfur dioxide pollution is reduced by reacting calcium oxide with sulfur dioxide to produce calcium sulfite.

7.00 g of calcium oxide reacts with an excess of sulfur dioxide. Relative atomic masses (A_r): O = 16 S = 32 Ca = 40 Calculate the mass of calcium sulfite produced.

Bleach is a solution of sodium hypochlorite (NaClO). Chlorine gas is produced when bleach reacts with hydrochloric acid. NaClO(aq) + 2HCl (aq) NaCl(aq) + H₂O(l) + Cl₂(g)

Give the test and result for chlorine gas.

Figure 8 shows a sealed flask of sodium hypochlorite and hydrochloric acid at equilibrium.

Explain why equilibrium is reached in this reaction.

The stopper in Figure 8 is removed and hydrochloric acid is added. The stopper is replaced. Explain what happens to the equilibrium.

Chlorine gas is also produced when hydrogen chloride decomposes.

The forward reaction is endothermic.

Predict the effect of increasing the temperature on the amount of chlorine gas produced at equilibrium. Explain your answer using Le Chatelier’s Principle.

Explain the effect of increasing the pressure on this equilibrium.