Topic 4 Crude Oil & Atmosphere

2.9 Percentages of the 4 most abundant gases in dry air

• Nitrogen 78%

• Oxygen 21%

• Argon 0.9 %

• Carbon dioxide 0.037 %

2.10+2.14 Determine the percentage by volume of oxygen in air using experiments involving the reactions of metals e.g. copper

1. Using gas syringes, 100 cm³ of air is passed from side to side over copper that is being heated by a bunsen burner(→ increase rate of reaction)

2. All oxygen from the air will react with copper to form copper oxide, reducing the total air volume.

3. The copper will turn black because it has been oxidised (copper oxide will form which is black)

4. It is a closed system, so no air can go in or out.

5. Continue until the volume stops decreasing then record the remaining air volume.

6. It should be about 79cm³ left, showing that 21 cm³ of the original 100 cm³ air was oxygen. 21/100 = 21% (Calculate percentage change)

Equation : 2Cu + O₂ → 2 CuO

2.10+2.14 Determine the percentage by volume of oxygen in air using experiments involving the reactions of metals e.g. copper

1. Place the phosphorus in an evaporating dish and float the dish in a water bath

2. Ignite the phosphorous and then quickly place a bell jar into the water bath, covering the dish.

3. Take a note of the starting height of the water level in the bell jar.

4. The water level will rise because ignited phosphorus will react with the oygen in the air (combustion of phosphorus), reducing the air pressure inside the bell jar. The external atmospheric pressure is greater, so it causes the water level inside the bell jar to rise.

5. Leave apparatus until the phosphorus is extinguished.

6. Measure the final water level in the bell jar. The decrease in the volume of air is the volume of oxygen originally in jar. Calculate percentage of oxygen in air.

2.11 Combustion of elements in oxygen

When elements are burnt in oxygen, they form oxides of the elements.

Metal + oxygen:

→ Metal oxide （would form alkaline solutions in water)

e.g. magnesium + oxygen → magnesium oxide

2 Mg + O₂ → 2 MgO (formula of this ionic compound determined using the crossing method, balancing charges)

Non-metal + oxygen:

→ non-metal mon-(1)/di-(2)/tri-(3)/pent-(5) oxide

Common metal oxides:

• hydrogen : H₂O water

• sulfur : SO₂ Sulfur dioxide

• nitrogen: NO nitrogen MONoxide

• carbon : CO₂ carbon dioxide

• silicon : SiO₂ silicon dioxide

• phosphorus: P₂O₅ diphosphorus pentoxide

Combustion of compounds in oxygen (products)

→ “sum” of Oxidation of the different elements present in the compound

e.g. hydrogen sulfide (H₂S) + oxygen→water + sulfur dioxide

2.12 describe the formation of carbon dioxide from the thermal decomposition of metal carbonates, including copper (II) carbonate

Thermal decomposition = the breaking down of a compound using heat

Thermal decomposition of metal carbonate produces metal oxide and carbon dioxide.

metal carbonate →_heat metal oxide + CO_{2 (carbon dioxide)}

• When copper carbonate (which is a green powder) is heated, copper oxide (which is black/so it will turn black) and carbon dioxide (CO₂) are formed.

• Limewater can be used to test the presence of carbon dioxide. It turns cloudy when carbon dioxide is bubbled through it. (Connect boiling tube containing heated copper carbonate to a boiling tube containing lime water using a delivery tube)

2.13 Carbon dioxide and its effect on climate

Carbon dioxide is a greenhouse gas because it absorbs infra-red radiation and traps heat in the atmosphere, contributing to climate change.

→ increasing amount of CO₂ in the atmosphere contributes to climate change.

1.1 Particles of a solid (arrangement, movement, energy)

Particles in a solid:

• have a regular arrangement

• vibrate around fixed positions

• have low energy

1.1 Particles of a liquid (arrangement, movement, energy)

Particles of a liquid:

• have irregular/random arrangement

• move one over another, they flow

• have more energy than solid particles but less energy than gas particles

1.1 Particles of a gas (arrangement, movement, energy)

Particles of a gas:

• have irregular arrangement

• move randomly and rapidly in all directions, they flow

• have high energy

1.2 Interconversions between 3 states of matter

Interconversion taking place at Melting point:

solid → liquid : melting (endothermic)

liquid → solid : feezing (exothermic)

Interconversion taking place at Boiling point:

liquid → gas : evaporating (endothermic)

gas → liquid : condensing (exothermic)

(solid → gas : sublimation and gas→ solid: deposition)

when you change from solid to liquid to gas:

• the particles gain more kinetic energy,

• they move around more and

• become more randomly arranged and further apart

• when you change from gas to liquid to solid:

• the particles lose kinetic energy,

• they move less and

• become more regularly arranged and closer together

1.8 Element, compound, mixture definitions

• Element = a substance consiting only of one type of atom

• Compound = a substance made of 2 or more elements chemically joined/combined(reacted) together

• Elements and compounds are pure substances

• Mixture = a substance consisting of 2 or more elements or compounds not chemically joined together.

→Chemical properties of each substance in a mixture remain unchanged. (e.g. melting and boiling point)

1.9 melting & boiling points of pure substances and mixtures

• Pure substances (elements and compounds) have fixed melting & boiling points.

• Mixtures boil and melt over a range of temperatures because different substances in the mixture can have different melting & boiling points.

1.10 Simple distillation

→Used to separate solute and solvent from a solution

• Heat the solution(e.g. salt solution) using a bunsen burner

• The solvent(liquid, e.g. wazer) has a lower boiling point, so it will evaporate from the solution.

• It is then cooled and condensed (in a Liebig condenser) and collected in a separate beaker/container/flask.

• The solute (e.g. salt) will stay in the flask. Turn off the bunsen burner as soon as all the liquid has evaporated.

Fractional distillation

→Used to separate a mixture of different liquids, e.g. ethanol and water

• heat the mixture (in a distillation flask)

• The liquid with lower boiling point (e.g. ethanol) vaporises first, it rises through a fractionating column (containing glassbeads, allowing repeated condensation and vaporisation) and condenses in a Liebig condenser, and condensed liquid will be collected in a separate flask.

• The liquid with higher boiling point (e.g. water) mainly stays in the distillation flask. (If it vaporises, it rises to the fractionating column, and gets cooled by the glassbeads, causing it to condense and fall back to the distillation flask again.)

4.7 What is crude oil

Crude oil is a mixture of hydrocarbons.(compounds only containing hydrogen and carbon)

4.8 describe how industrial process of fractional distillation separates crude oil into fractions

1) The crude oil is heated and vapourised

2) The vapour enters a fractionating tower, which is hottest at the base and coolest at the top.

3) The vapours rise in the tower until the temperature is less than the boiling point, where they condense.

4) They are then collected in fractions, which are mixtures of hydrocarbons of similar carbon chain length./similar number of carbon atoms

4.9 Main fractions obtained from crude oil

From top to bottom:

• Refinery gas (used as fuel for domestic heating and cooking e.g. for camping stove)

• Gasoline (used as fuel for cars)

• Kerosine (fuel for aircraft)

• Diesel (fuel for some cars/lorries and trains)

• Fuel oil (used for ships)

• Bitumen (used for the surface of roads or roofs)

4.10 trend in colour, boiling point, viscosity (and number of carbon atoms) of the main fractions

Fractions at the top:

• lightest in colour

• lowest boiling point(most volatile and flammable)

• least viscous (not thick, flows)

• less carbon atoms (smaller size molecules)

Fractions at the bottom:

• darkest in colour

• higher boiling point(least volatile and flammable)

• most viscous (think and does not flow)

• most carbon atoms (bigger size molecules)

4.11 What is a fuel?

Fuel is a substance that releases heat / thermal energy when burned.

Burning is a combustion reaction. A substance reacts with oxygen.

4.12 know the possible products of complete and incomplete combustion of hydrocarbons with oxygen in the air

• Hydrocarbons are good fuels. When they are burned in oxygen(in the air), the combustion reaction releases a lot of thermal energy. (exothermic reaction)

• Complete combustion of hydrocarbons produces carbon dioxide and water

• Incomplete combustion of hydrocarbons produces a mixture of soot (black carbon powder) and carbon monoxide.

• Incomplete combustion occurs when there is not enough oxygen.

4.13 Why is carbon monoxide bad?

Carbon monoxide is poisonous. It reduces the capacity of blood to transport oxygen around the body. (because it binds to haemoglobin)

4.14+4.16 What gas is formed in car engines and why does it contribute to pollution ?

In car engines, the temperature is high enough for nitrogen to react with oxygen, forming nitrogen oxides. Nitrogen oxides react with rain water to form nitric acid, contributing to acid rain.

4.15+4.16 Why can combustion of impure hydrocarbon fuels contribute to pollution?

Crude oil is not a pure hydrocarbon fuel. It may be impure and also contain sulfur. When burning hydrocarbons containing sulfur, sulfur dioxide is formed. When sulfur dioxide reacts with rainwater, sulfurous acid is formed, contributing to acid rain.

Acid rain consequences

• kill aquatic animals

• kill plants

• Iron rusts

• Damage/erode marbles