Gas Production and Testing: Oxygen, Carbon Dioxide, and Hydrogen

At the end of this unit you should: 1. Be able to produce gases, in particular oxygen, carbon dioxide and hydrogen. 2. Be able to carry out the characteristic tests for oxygen, carbon dioxide and hydrogen gases. 3. Be able to identify some of the properties of carbon dioxide. 4. Be able to explain combustion and the fire triangle. 5. Know how to compare and contrast combustion, respiration and photosynthesis as chemical reactions. 6. Understand that the atmosphere is a mixture of gases in a number of layers.

At the end of this unit you should: 7. Be able to test for the presence of oxygen, carbon dioxide and water vapour in the air. 8. Understand the Law of Conservation of Mass through the production and identification of a gas. 9. Understand the role of carbon dioxide in photosynthesis and extinguishing fire.

activation energy aerobic respiration anaerobic respiration atmosphere characteristic test combustion downward displacement exothermic fire triangle fuel Law of Conservation of Mass Phlogiston Theory photosynthesis respiration upward displacement

LIGHTBULB QUESTION Oxygen is a flammable gas that humans need to live. It is part of the fire triangle and it is required for respiration, which allows energy to be created in the body.

Aerobic Respiration: The release of energy from nutrients in organisms by chemical reaction with oxygen. Anaerobic Respiration: The release of energy from nutrients in organisms without a chemical reaction with oxygen.

Combustion: The release of heat energy from substances by chemical reaction with oxygen. Fuel: A substance that releases its chemical energy as heat energy when reacted with oxygen.

Fire Triangle: The three factors that are needed for combustion: fuel, heat energy and oxygen.

Activation Energy: The minimum amount of energy needed for a reaction to happen. Exothermic: A chemical reaction in which energy is released into the surroundings.

Equipment: Water trough, tea-light candle, graduated cylinder, large tap funnel and retort stand or large graduated cylinder and beehive shelf or large beaker and wood chocks, matches, permanent felt marker. Variation 1: Investigation 09.01.01: How much of air is oxygen?

Instructions Variation 1: 1. Fill a water trough to between ⅓ and ½ its volume with tap water. 2. The tap on the funnel should be put in the open position. The tap funnel should then be lowered into the water and the water level marked on its outside with the felt marker. 3. Light a tea-light candle and place it floating in the water trough. 4. The candle should be allowed to burn until a strong consistent flame can be seen (maximum of approximately three minutes). 5. The tap funnel should be lowered over the candle, taking care not to capsize the candle. 6. Once the water levels inside and outside the tap funnel have levelled, the tap can be closed. 7. As the oxygen is consumed by the candle flame, the internal water level will rise significantly and the external level fall slightly.

Instructions Variation 1: 8. Once the candle has been extinguished, the change in the internal water level should be noted by marking the outside of the funnel. 9. The tap funnel can be removed and the tap closed before filling it with water to the first marking. 10. The tap should be opened over a graduated cylinder until the water level drops to the second marking. This volume should be noted. 11. The remainder of the water in the funnel should also be measured and total water in the funnel also recorded. 12. The first (smaller) water volume should be calculated as a percentage of the total water volume.

Instructions Variation 2: 1. Fill a water trough to between ⅓ and ½ its volume with tap water. 2. Place a beehive shelf at the bottom of the water trough. 3. Place an inverted large graduated cylinder over the beehive shelf and note the internal water level. 4. Light a tea-light candle and place it floating in the water trough. 5. The candle should be allowed to burn until a strong consistent flame can be seen (maximum of approximately three minutes). 6. The graduated cylinder should be lowered over the candle at a slight angle, taking care not to capsize the candle. The water levels should then equalise.

Instructions Variation 2: 7. Once the burning candle has consumed the available internal oxygen, the water level will rise. The new internal level should be noted. 8. Using the volume measurements noted from the graduated cylinder, the percentage of oxygen in air can be calculated.

Instructions Variation 3: 1. Fill a water trough to between ⅓ and ½ its volume with tap water. 2. Place two wooden chocks on the base of the water trough so that they can support a large beaker. 3. Place an inverted large beaker cylinder over the beehive shelf and note the internal water level. 4. Light a tea-light candle and place it floating in the water trough. 5. The candle should be allowed to burn until a strong consistent flame can be seen (maximum of approximately three minutes). 6. The large beaker should be lowered over the candle at a slight angle, taking care not to capsize the candle. The water levels should then equalise.

Instructions Variation 3: 7. Once the burning candle has consumed the available internal oxygen, the water level will rise. The new internal level should be marked on the outside of the beaker. 8. The beaker can then be removed and filled with water to the first marking. 9. The beaker should be emptied until the water level drops to the second marking. This volume should be noted. 10. The remainder of the water in the beaker should also be measured and total water in the beaker also recorded. 11. The first (smaller) water volume should be calculated as a percentage of the total water volume.

1. Can another source of flame instead of a candle be used for this investigation? Justify your answer. • Candles are made from paraffin wax so are naturally waterproof and will not soak up any water to quench the flame. A candle will also float easily on water. A wide candle could also be cut to a thick disc shape and used instead of a tea-light. A small ‘boat’ of tinfoil could be used to burn some other material, but this may become swamped when covering it.

2. Could the size or shape of the candle, or other pieces of equipment, make a difference to the results of your investigation? • No – the investigation is testing the volume of air inside the container that is left after displacement by any solids such as the candle. Regardless of the sizes used, there is a fixed proportion of oxygen available, so size becomes irrelevant.

3. Can you explain why the flame on the candle should be left lit for a few minutes before the upside-down container is placed over it? • This allows the wax to melt sufficiently so it can then be burned, creating convection currents that draw in more air until the combustion has reached a self-sustaining temperature.

4. How can you stop water swamping the candle as you place the upside-down container over it? • Regardless of the container used, it must be placed slowly over the candle to prevent capsizing and splashing if it rises unevenly within the container.

5. Can you think of a way to measure the amount of oxygen used by the flame? • If not using a large graduated cylinder as the container, carefully marking the changing water levels on the outside of the container and measuring the different volumes with a graduated cylinder will work.

6. Suggest reasons why your measurement might not be accurate and how you could improve accuracy in this investigation? • Allowing the candle to burn long enough should mean that the flame in the container consumes the oxygen quickly and at a higher temperature, so should combust better than if it was only just lit, as well as reducing the amount of smoke (partly combusted fuel). Practice will increase dexterity and accuracy also.

7. Other chemical reactions also use oxygen from the atmosphere. Is there a reaction you can use to get a more accurate measurement of oxygen used? • The rust reaction using steel wool instead of a candle can be more accurate. The most accurate way is to pass oxygen over heated copper turnings, between two gas syringes.

8. In your opinion, is the percentage of oxygen in air always the same? Justify your answer. • No – oxygen in a room can be used up if there is no ventilation. This and the build-up of exhaled carbon dioxide leads to room becoming ‘stuffy’.

(a) Firefighters use water in most situations. Which factor in the fire triangle does using water remove? Heat. (b) Oil-well firefighters use explosives in the ‘blowout’ technique to extinguish oil-well fires. This is similar to blowing out birthday candles. Which factor in the fire triangle does this remove? Oxygen, because the air moves so fast past the flame it cannot use the oxygen for burning.

(c) Which factor is the most difficult to remove from a fire? Explain your answer. Fuel. It isn’t always possible to separate fuel from the heat or oxygen if it is one mass, e.g. a large log or a pool of liquid or gas.

Characteristic Test: A chemical test that identifies a specific substance and no other.

You are given three gas jars labelled X, Y and Z. You are told that a different gas has been placed in each gas jar. The three gases are oxygen, carbon dioxide and nitrogen. You have enough limewater to test all three gases, but only two wooden splints, so you can only test two gases with these. How would you carry out an investigation to identify the three gases? Test two gas jars with glowing splints. If one relights, oxygen has been identified. If neither relights the untested gas jar is oxygen. The two gas jars can then be tested with limewater to distinguish between carbon dioxide and nitrogen. The one that does not turn limewater milky is nitrogen.

Law of Conservation of Mass: Matter can be neither created nor destroyed but rather converted from one form to another.

Equipment: Top-pan balance, empty small soft drinks bottle, rubber balloon, elastic band, baking powder (sodium bicarbonate), teaspoon, vinegar. Investigation 09.01.02: Confirming the Law of Conservation of Mass

Instructions: 1. Place 50 cm3 of vinegar in a clean, dry soft drinks bottle. 2. Stretch the rubber balloon several times and then add two–three teaspoons of vinegar to it. 3. Place the bottle, balloon and elastic band onto the top-pan balance. Note the total mass. 4. Stretch the neck of the balloon over the neck of the bottle, and fix in place with the elastic band. 5. Lift the bottom of the balloon up to tip the baking powder into the bottle. 6. Allow the reaction to continue until no more gas is produced (bubbling stops). 7. Note the total mass.

1. How could you identify this gas? • Test with limewater first. If it does not give a positive test, testing with a glowing splint will establish if it is oxygen or not.

2. Is this a good method to demonstrate the Law of Conservation of Mass? Justify your answer. • Yes – the equipment is simple and easy to use, and it is possible to measure changes in state of matter without losing any gas.

3. Can you think of other substances that could be used to prove the Law of Conservation of Mass with a different gas? • Hydrogen peroxide can be substituted for vinegar, and a small amount of manganese dioxide for the baking powder, to produce oxygen using the same equipment.

Investigation 09.01.03: Identifying the properties of three unknown gases Equipment for Method 1: Conical flask (or Buchner flask), two-hole stopper (or one-hole), delivery tube, tap funnel, three gas jars and covers, cardboard cover with central hole, 20 g of medium-size marble chips, 250 ml of 0.3 M hydrochloric acid, retort stand and clamp.

Instructions for Method 1: 1. Add the marble chips to the flask. 2. Seal the flask with the stopper and make sure the tap of the funnel is closed. 3. Clamp the flask at the neck to prevent toppling. 4. Fill the reservoir of the tap funnel. 5. Connect the delivery tube to the flask and pass through the cover of the gas jar. 6. Allow approximately half the volume of the tap funnel to run into the flask, making sure to close the tap after doing this.

Instructions for Method 1: 7. Allow the reaction to continue for ninety seconds before replacing the first gas jar with another. 8. Test the gas by adding a small amount of limewater and shaking. 9. The second gas jar can be tested with limewater. Also test with a lighted splint and a glowing splint.

Investigation 09.01.03: Identifying the properties of three unknown gases Equipment for Method 2: Conical flask (or Buchner flask), two-hole stopper (or one-hole), delivery tube, beehive shelf, tap funnel, three large test tubes with stoppers, test tube stand, 20 g of zinc granules, 250 ml of 0.3 M hydrochloric acid, two retort stands and clamps.

Instructions for Method 2: 1. Two-thirds fill the water trough and place a beehive shelf in the centre of the trough. 2. Place the delivery tube so that it runs from the flask and up through the beehive shelf. The tube should only slightly protrude above the top of the beehive shelf. 3. Fill the test tubes with water, by slowly immersing in the water at an angle. This allows all the air to escape. 4. Invert one test tube and place it over the centre of the beehive shelf. Secure by clamping in a retort stand. 5. Allow approximately half the volume of the tap funnel to run into the flask, making sure to close the tap after doing this.

Instructions for Method 2: 6. Allow the reaction to continue for approximately thirty seconds as this allows the air in the system to be expelled. Air will bubble out from under the test tube/beehive shelf as this happens. 7. Stopper the test tube under the water level and substitute with another test tube. 8. Test the filled test tube by removing the stopper and quickly placing a lit splint into the mouth of the tube. Also test with limewater and a glowing splint.

Investigation 09.01.03: Identifying the properties of three unknown gases Equipment for Method 3: Conical flask (or Buchner flask), two-hole stopper (or one-hole), delivery tube, tap funnel, water trough, three gas jars and covers, 10 g–15 g of manganese dioxide, 250 ml of ‘40 volume’ hydrogen peroxide, retort stand and clamp.

Instructions for Method 3: 1. Two-thirds fill the water trough and place a beehive shelf in the centre of the trough. 2. Place the delivery tube so that it runs from the flask and up through the beehive shelf. The tube should only slightly protrude above the top of the beehive shelf. 3. Fill the gas jars with water by slowly immersing in the water at an angle. This allows all the air to escape. 4. Invert one gas jar and place it over the centre of the beehive shelf. 5. Allow approximately half the volume of the tap funnel to run into the flask, making sure to close the tap after doing this.

Instructions for Method 3: 6. Allow the reaction to continue for approximately ninety seconds as this allows the air in the system to be expelled. Air will bubble out from under the gas jar/beehive shelf as this happens. 7. Cover the gas jar under water so that no gas is lost. 8. Test the gas with a glowing splint. Also test with limewater and a burning splint.

1. How can you prove which gas is heavier than air? • Compare the mass of a sealed container of each gas with the mass of a sealed container of air. Alternatively, a rubber balloon could be filled with each gas and then dropped to see which falls through the air.

2. Should you rely on the first sample of each gas that you collect? Explain your answer. • No, as it may be contaminated with air from the apparatus. The second sample should also be tested to confirm the initial result.

3. Does solid F get used up? Why do you think this happens? • Solid F does not get used up. It is a catalyst and is there to speed up the reaction by reducing the activation energy without getting used up itself.

(a) Using the information above and the information given to you by your teacher, write a word equation for each gas production reaction: Gas X reaction: liquid A + solid B → salt + water + gas X Gas X reaction: hydrochloric acid + marble chips → calcium chloride + water + carbon dioxide Gas Y reaction: liquid C + solid D → salt + gas Y Gas Y reaction: hydrochloric acid + zinc → zinc chloride + hydrogen Gas Z reaction: liquid E water + gas Z Gas Z reaction: hydrogen peroxide water + oxygen Solid F manganese dioxide

(b) When you have completed the word equations, write the chemical equations using the chemical formula for each substance.

Gas Production and Testing: Oxygen, Carbon Dioxide, and Hydrogen