topic 8 - exam qs

• The Earth's atmosphere today has changed. State how cooling of the atmosphere changed the composition of the Earth's atmosphere:

  Cooling condensed the water vapour in the air and this formed oceans therefore getting rid of water vapour.
• The Earth's atmosphere today has changed. Explain how photosynthesis has changed the composition of the Earth's atmosphere.

  Carbon dioxide level reduces as oxygen level increases as carbon is turned into oxygen
• After the reaction between dry air and copper, what is the gas that takes up most of the remaining gas in the apparatus?

  Nitrogen
• Nitrogen takes up most of the atmosphere, then oxygen, then other gases
• What is the test for oxygen?

  Hold a glowing splint next to a test tube of oxygen, if it relights then the gas is oxygen
• State why an excess of copper must be used:

  To ensure that all oxygen is removed from the copper

  
• How can you find the volume of oxygen in 100 cm3 of air from the copper experiment?

  Measure the volume of gas in the syringe at the end and then subtract it from the original volume of gas

  
• What is the percentage of carbon dioxide in the Earth's atmosphere today?

  Less than 0.5%
• The percentage of carbon dioxide in the Earth's atmosphere today is less than that in the Earth's earliest atmosphere. Explain what has caused the percentage of carbon dioxide to decrease:

  Carbon dioxide is dissolved in the oceans and is incorporated into marine organisms forming carbonate rocks. This causes an increase in plant growth and therefore photosynthesis increases removing carbon dioxide.
• How do pollutant gases in the atmosphere help to keep the Earth warm?

  They reflect sunlight or heat back to Earth increasing global temperatures
• Explain why the water level had risen:

  The volume of gas in the bell jar decreases as oxygen is removed from the air and water rises to fill the space

  
• Dilute sulfuric acid was added to magnesium oxide. State the name of the salt formed.

  Magnesium sulphate
• Explain why it is difficult to be precise about the composition of the Earth's early atmosphere.

  Nobody was there therefore limited evidence is provided and there are no records of the Earth's atmosphere. There are gases trapped in ice cores however this doesn't explain anything very far into the past.
• As the Earth cooled, oceans formed. How did this affect the composition of the atmosphere?

  The amount of water vapour is lowered and the oceans absorbed carbon dioxide
• State another cause, other than the increase in fossil fuels being burnt, of increasing amounts of carbon dioxide in the atmosphere:

  Deforestation, volcanic activity, respiration, increase in temperature
• How would you describe the relative amounts of carbon dioxide and oxygen in the Earth's early atmosphere?

  Large amount of carbon dioxide and small amount of oxygen
• Which gases are greenhouse gases?

  Water vapour, methane
• State one factor that makes a good fuel:

  Burns easily, produces little ash, produces little smoke, produces high heat energy per unit mass, is easy to store or transport
• Bioethanol is a fuel that can be obtained from the plant, sugar beet. Explain one advantage of using bioethanol produced from sugar beet, rather than petrol produced from crude oil.

  Renewable, crude oil is finite, less energy is required for bioethanol production
• Explain how the petrol and bitumen fractions differ in their properties and uses:


  Petrol has shorter carbon chains and therefore a lower melting point, boiling point and viscosity. Petrol ignites more easily and bitumen does not combust completely due to high number of carbon atoms per molecule. Petrol is used as fuel for cars, motorbikes and transportation. Bitumen is used for road surfacing and roofing or flooring.

  
• What is a trend from the top of the fractionating column to the bottom?

  The ease of ignition decreases
• Describe the problems caused by one product of the incomplete combustion of a hydrocarbon fuel:

  Carbon monoxide is toxic, soot causes respiratory problems
• When fuel oil is burnt, carbon dioxide is produced and released into the atmosphere. Explain why some people are concerned about the release of large quantities of carbon dioxide into the atmosphere.

  Carbon dioxide is a greenhouse gas so it traps heat in the atmosphere and may lead to an increase in global temperature
• Fuel oil can contain sulfur as an impurity. Explain how burning this impurity can cause problems in the environment.

  Sulphur combusts and forms sulphur dioxide which dissolves in rain creating acid rain. This would cause damage towards limestone statues and crops and it could kill fish.
• Crude oil is a source of many fuels. These fuels are known as fossil fuels. Describe the advantages of replacing fossil fuels with biofuels.


  Biofuels are renewable but fossil fuels are sustainable as they are produced from plants. Biofuels do not contain impurities like sulphur meaning it won't be as damaging to the environment and growing plants removes carbon dioxide from the atmosphere.
• State what you would do to prevent this:

  Remove delivery tube from water before stopping heating

  
• Propane and propene are bubbled through separate samples of bromine water. Describe what you would see in these tests.

  When propene is added, the bromine water will go from orange to clear. When propane is added, the bromine water remains orange.
• In industry, long chain hydrocarbon molecules are cracked to form shorter chain hydrocarbon molecules. Explain why this process is important

  This process is called cracking. Shorter chain molecules are more useful and there is higher demand for them. It also produces alkenes that are used to make polymers making materials like plastic bags.
• Explain the difference between non-renewable and renewable fuels:

  Non-renewable fuels are of a finite supply and renewable fuels are produced from plants therefore when used it is able to be replaced
• What are the advantages of using bioethanol, instead of petrol, as a fuel for cars.

  Bioethanol is renewable but petrol is finite

  Crops to make bioethanol can be regrown quickly but crude oil takes a long time to form

  The use of Bioethanol reduces the demand for fossil fuels

  Carbon dioxide is removed from the air when growing crops that are used in ethanol production

  There may be sulphur impurities in petrol but there are none in ethanol and ethanol as a result is less polluting

  Ethanol burns more completely, petrol does not
• What are the disadvantages of using bioethanol, instead of petrol, as a fuel for cars?


  Bioethanol is less readily available than petrol and there are fewer filling stations than for petrol (in the UK)

  Lots of crops are needed to generate sufficient fuel to replace petrol

  Less farmland is available for growth of crops

  Currently, few cars are built to run on bioethanol and this is probably because it runs out faster and is less energy efficient
• Apart from the possibility of an explosion, state another disadvantage of using hydrogen, rather than diesel, as a fuel for buses:

  It requires electricity for electrolysis, it must be stored in pressurised cylinders, gas can escape easily, there are fewer fuel stations