2023

• which chemical element does all gases contain?

  oxygen
• Where does nitrogen come from?

  Air
• What environmental effect do particulates from burning diesel cause?

  Global dimming
• Give one reason why carbon monoxide is difficult to detect

  -colourless

  -odourless
• Explain why water vapour and not liquid water is produced when diesel burns

  -Diesel burns at a higher temp, greater than 100 °C

  -which is above the boiling point of water
• Why does sulfur cause an environmental problem

  -Sulfur dioxide is produced when diesel is burned

  -which causes acid rain

  -damage to building/trees & respiratory problems
• 2 phases of chromatography

  -mobile phase

  -stationary phase
• Why do the substances in the mixture separate in the mobile phase

  -substance moves at different speeds

  -Substances move at different solubilities
• How many spots are produced on the chromatogram for a pure compound

  1
• Give 2 reasons why crude oil is not a formulation

  -Crude oil is a mixture, but not a useful product

  -and not mixed carefully measured quantities
• Describe how crude oil is separated into fractions

  -crude oil is heated to vaporise the hydrocarbons

  -The temperature of the column decreases from bottom to top

  -so the hydrocarbons condenses at different heights(in the column)

  -because the hydrocarbons have different boiling points
• Why are alkanes cracked

  -to make smaller hydrocarbon molecules

  -which are more useful products/useful as fuels
• hydrogen test

  test-buring splint

  Result -burns with a squeaky pop sound
• Alkenes -the general formula for the homologous series of alkenes is $C_nH_{2n}$


  formula represents an alkene-$C_2H_4$
• if not given valid result

  heat the evaporating basin & contents to constant mass
• A test that distilled water is pure

  test-determine the boiling point

  Result: pure water boils at 100°C

  Or

  test-detrmine the freezing point

  Result: pure water freezes at 0c
• $⇌$


  reversible reaction symbol
• temp increased

  equilibrium shifts to the left
• test to identify the gas used to sterilise water

  test-damp litmus paper

  result-litmus paper bleached
• Why does potable water contain dissolved solids after filtering

  The dissolved solids pass through the filter paper because the dissolved solid particles are very small
• Give one effect of global climate change

  -melting ice

  -flooding

  -extreme weather

  -loss of habitats

  -rising sea levels
• Explain how greenhouse gases cause global warming

  -Greenhouse gas allows short-wavelength radiation to enter the atmosphere

  -which is absorbed by Earth and re-emitted as longer wavelength radiation

  -which is absorbed by greenhouse gas in the atmosphere

  -This increases the temperature leading to global warming
• Explain how planting trees reduces global warming

  -Trees use $CO_2$

  -for photosynthesis

  -and $CO_2$ causes global warming
• Oxygen test for gas

  test-glowing splint

  result-relights
• why using a bigger value like(20) better than using (10)

  -smaller volume of gas produced(per unit time)

  -So, error in reading is a larger percentage of the total volume
• systematic error in the investigation

  timer slow/fast
• Q1.2 Compare the properties of petrol and diesel. Use Table 1. (2 marks)A:

  • Hydrocarbon molecules in petrol have fewer carbon atoms (4 to 12) than in diesel (12 to 20)
  • Petrol has a lower boiling point range (40–205 °C) than diesel (250–350 °C)
• Q5 Black ink is a mixture of several colours.Plan an experiment using paper chromatography to:

  • separate the colours in black ink

  • identify the colours from their Rf values.(6 marks)

  A:

  • Draw a pencil line near the bottom of the chromatography paper
  • Put a small dot of black ink on the pencil line and add a small volume of water (solvent) to a beaker
  • Place the chromatography paper in the solvent, making sure the ink dot is above the level of the solvent
  • Support the paper in this position and place a lid on the beaker
  • Allow the solvent to run up the paper, then mark the final solvent front and leave to dry
  • Calculate Rf values: measure the distance moved by each dye and the solvent front, then divide (Rf = distance moved by spot ÷ distance moved by solvent) and compare with known Rf values to identify the colours