2.5 Crude Oil, Fuels & Organic Chemistry (WJEC GCSE Chemistry): Flashcards

False.

Smaller hydrocarbon molecules are more flammable and easier to ignite. Larger molecules have stronger intermolecular forces and are less flammable, making them more useful as lubricants than fuels.

Viscosity is a measure of how easily a liquid flows. High-viscosity liquids are thick and flow less easily; low-viscosity liquids are runny.

Bitumen is used for surfacing roads and roofs.

False.

Shorter-chain hydrocarbons burn with a cleaner, bluer flame. Longer-chain hydrocarbons burn with a more yellow, smoky flame because there is insufficient oxygen to react with all the atoms in the larger molecules.

The gasoline/petrol fraction is used as fuel for cars, while the fuel oil fraction is used as fuel for ships and power stations.

Larger hydrocarbon molecules have higher boiling points because they have larger intermolecular forces of attraction, which require more energy to overcome.

Burning crude oil releases large amounts of carbon dioxide, a greenhouse gas. This contributes to global warming and climate change.

Acid rain is caused when fuels containing sulfur impurities are burned, producing sulfur dioxide gas, which dissolves in rainwater to form acid rain.

False.

Oil spillages and the pollutants from burning crude oil affect the environment everywhere, not just the countries that produce or use the oil. They can destroy habitats and kill animals across wide areas.

As demand for crude oil increases and supplies diminish, the price of fuel will increase, which will indirectly affect heating and travel costs.

One political impact is that war or conflict in oil-producing countries can result in oil supplies being cut off to other countries, threatening energy security.

False.

Crude oil is also used to make many important products such as plastics and medicines. This creates a difficult choice between burning remaining reserves or using them as raw materials.

Increasing global demand poses a sustainability problem because crude oil is a finite resource. It is consumed much faster than it can be replaced, so supplies will eventually run out.

Complete combustion is the reaction of a fuel with plenty of oxygen, where all elements in the fuel react fully with oxygen to produce carbon dioxide and water only.

When a hydrocarbon undergoes complete combustion, carbon dioxide and water are produced.

When balancing combustion equations, balance the carbon atoms first, then the hydrogen atoms, and finally the oxygen atoms.

True.

Combustion reactions release energy to the surroundings, making them exothermic. This is why fuels are burned to provide heat and energy.

The balanced equation for the complete combustion of methane is: CH₄ + 2O₂ → CO₂ + 2H₂O.

A fuel is a substance that reacts with oxygen to release energy. This type of reaction is called combustion.

The balanced equation is: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. There are 3 carbons, so 3CO₂; 8 hydrogens, so 4H₂O; and 10 oxygen atoms on the right, so 5O₂ on the left.

True.

By definition, a hydrocarbon contains hydrogen and carbon atoms only.

Specific heat capacity is the energy needed to raise the temperature of 1 g of a substance by 1 °C. The specific heat capacity of water is 4.18 J/g/°C.

Calorimetry is used to measure the energy released by a fuel. A fuel is burned under a container of water, and the temperature rise of the water is recorded.

The heat energy change Q is calculated using Q = m x c x DT, where m is the mass of water, c is the specific heat capacity, and DT is the temperature change.

False.

A negative value of Q indicates the reaction is exothermic (energy is released to the surroundings). An endothermic reaction would give a positive Q value.

Q = m x c x DT = 200 x 4.18 x 30 = 25 000 J. The temperature change DT = 50 - 20 = 30 °C.

The spirit burner is weighed before and after to calculate the mass of fuel burned, which is needed to determine the energy released per gram of fuel.

False.

You do not need to recall Q = mcDT, as it will be provided in the exam. However, you must be able to use it to calculate the energy released by a fuel from data given.

A spirit burner containing the fuel is placed beneath a conical flask of water on a clamp stand. A thermometer measures the temperature change of the water.

In the fuel energy experiment, the mass of the spirit burner before and after burning is recorded, and the temperature of the water is measured throughout.

False.

The thermometer must not touch the bottom of the conical flask, as this would give an inaccurate temperature reading. It should measure the temperature of the water, not the flask itself.

Alcohols are highly flammable and should be burned in a well-ventilated laboratory, away from other flames, to reduce the risk of fire and ensure safety.

The trend suggests that larger alcohol molecules release more energy per gram when burned. Energy released per gram increases as the size of the alcohol molecule increases.

Energy released per gram of fuel = (mass of water x temperature change x 4.2) divided by the mass of alcohol burned.

False.

Different fuels release different amounts of energy per gram when burned. This experiment is designed specifically to compare the energy released per gram across different fuels such as methanol, ethanol, propanol, and butanol.

When hydrogen burns as a fuel: hydrogen + oxygen → water. This is an exothermic reaction.

False.

Burning hydrogen produces only water as a product. It does not produce carbon dioxide or sulfur dioxide, so it does not contribute to global warming or acid rain.

Hydrogen is obtained from water by the process of electrolysis. This requires large amounts of electricity to carry out.

Two disadvantages of hydrogen as a fuel are:

1. It requires large amounts of electricity to produce by electrolysis

2. It is difficult and dangerous to store because it forms an explosive mixture with air and requires pressurised containers.

A fuel cell is a device that uses the reaction between hydrogen and oxygen to generate electricity, producing only water as a by-product. It is used to power some cars and buses.

True.

Hydrogen is considered renewable because it is produced from water by electrolysis, which is an abundant resource. The combustion of hydrogen also produces water, completing the cycle.

The balanced equation for the combustion of hydrogen is: 2H₂ + O₂ → 2H₂O.

The three factors required for a fire are fuel, heat, and oxygen. Removing any one of these will extinguish or prevent a fire.

A fire can be extinguished by removing fuel, heat, or oxygen.

False.

Water is not suitable for electrical fires (increased risk of electric shock) or oil fires (water causes oil to form droplets, increasing the surface area and making the fire worse).

Carbon dioxide extinguishers and fire blankets work by removing oxygen from the fire. They cover the flames, reducing the oxygen available until the fire goes out.

A fire break is a section of forest or moorland where all fuel (vegetation) has been cut down and removed to prevent a fire from spreading across the area.

Closing doors confines the fire to a compartment with limited oxygen. Opening a door to a fire provides it with fresh oxygen, which makes it burn more intensely.

True.

Making materials fire-resistant reduces the amount of available fuel, which is the main focus of fire prevention according to the fire triangle.

Cracking is an industrial process used to break long-chain, low-demand hydrocarbon molecules into shorter, more useful hydrocarbon molecules.

Cracking is used because the demand for short-chain fractions (such as petrol) exceeds supply, while long-chain fractions are in excess. Cracking converts surplus long-chain hydrocarbons into more useful shorter ones.

During cracking, hydrocarbon vapours are passed over a hot powdered catalyst of alumina or silica at around 600-700 °C.

False.

Cracking produces a mixture of shorter alkanes and alkenes. Alkenes contain a carbon=carbon double bond (C=C) and are valuable as starting materials for making polymers such as polythene.

The balanced equation is: C₆H₁₄ → C₄H₁₀ + C₂H₄. The carbon and hydrogen atoms are conserved on both sides of the equation.

Check the general formula. Alkanes follow C_nH_2n+2, so all carbon-carbon bonds are single bonds. Alkenes follow C_nH_2n, indicating at least one carbon=carbon double bond.

True.

Alkenes such as ethene contain a reactive carbon=carbon double bond, which allows them to undergo addition polymerisation to form polymers like polythene.

A saturated hydrocarbon is a compound containing only single carbon-carbon bonds. Alkanes are examples of saturated hydrocarbons and follow the general formula C_nH_2n+2.

The general formula for alkanes is C_nH_2n+2, where n is the number of carbon atoms.

The alkane with 1 carbon atom is called methane. The alkane with 3 carbon atoms is called propane. The alkane with 5 carbon atoms is called pentane.

True.

Alkenes are unsaturated hydrocarbons because they contain at least one C=C double bond in addition to single bonds. This double bond is the functional group that makes alkenes reactive.

The general formula for alkenes is C_nH_2n, where n is the number of carbon atoms.

When naming a branched alkane, first identify the longest carbon chain, then identify the alkyl side-chain and the carbon number it is attached to.

False.

The smallest possible alkene has two carbon atoms (ethene, C₂H₄). A carbon-carbon double bond requires at least two carbon atoms.

C₄H₈ is an alkene. Substituting n = 4 into the alkene general formula C_nH_2n gives C₄H₈. The alkane formula C_nH_2n+2 would give C₄H₁₀, which does not match.

Isomers are compounds with the same molecular formula but a different structural formula.

The smallest alkane that can form isomers is butane (C₄H₁₀), which has two isomers.

False.

Propane has no isomers. There is only one way to arrange 3 carbon atoms with hydrogen atoms while obeying bonding rules (carbon = 4 bonds, hydrogen = 1 bond). The apparent second structure is identical to the first.

Isomers have the same molecular formula but different structural formulae.

C₅H₁₂ has three isomers: pentane (straight chain), methylbutane (one branch), and dimethylpropane (two branches on the central carbon).

True.

C₄H₈ has three isomers: but-1-ene (double bond between C1 and C2), but-2-ene (double bond between C2 and C3), and methylpropene (branched chain with the double bond).

A structural formula is a representation showing how atoms are arranged and bonded within a molecule, distinguishing it from other isomers with the same molecular formula.

To form the second isomer of C₄H₁₀, a CH₃ group is removed from the end of the chain and attached to the second carbon of the remaining chain.

An addition reaction is a reaction in which atoms from a simple molecule add across a C=C double bond, forming a single bond between the carbons and a saturated product.

When bromine water is added to an alkene, it decolourises from orange to colourless, because bromine adds across the C=C double bond.

When alkenes undergo addition reactions they form saturated compounds, because the C=C double bond opens and forms a single bond.

False.

Alkanes are saturated and have no C=C double bond. Bromine water remains orange when added to an alkane because no addition reaction can occur.

Hydrogenation is the addition reaction of an alkene with hydrogen gas (H₂) to produce an alkane.

The hydrogenation of ethene is: CH₂CH₂ + H₂ → CH₃CH₃. Hydrogen adds across the C=C double bond to produce ethane.

True.

Vegetable oils are polyunsaturated. Partial hydrogenation adds hydrogen across some of the C=C double bonds, reducing the number of double bonds and increasing the strength of the intermolecular forces between molecules. This raises the melting point, converting liquid oils into semi-solid fats used in margarine.

When bromine reacts with ethene, a bromoalkane is formed: CH₂CH₂ + Br₂ → CH₂BrCH₂Br. Bromine atoms add across the C=C double bond.

Addition polymerisation is a process in which small monomer molecules, each containing a C=C double bond, react together to form a long-chain polymer.

A monomer is a small molecule containing a carbon-carbon double bond (C=C) that can react with many identical molecules to form a polymer.

False.

One of the two bonds in each C=C double bond breaks open during addition polymerisation. The resulting polymer contains only single C–C bonds.

To name a polymer, the name of the monomer is placed in brackets and the prefix poly- is added.

The monomer used to make poly(propene) is propene. Propene molecules contain a C=C double bond that opens up to join adjacent molecules during polymerisation.

True.

Polythene is an exception to the standard naming convention. Although the systematic name would be poly(ethene), it is known as polythene.

The lower case n represents a large, unspecified number of monomer molecules that react together. It appears in front of the monomer and after the polymer brackets.

Poly(vinylchloride) is made from the monomer vinylchloride. Poly(tetrafluoroethene) is made from the monomer tetrafluoroethene.

Poly(vinylchloride) is used to insulate electrical wiring because it is an excellent electrical insulator, which prevents electric shocks and overheating.

False.

Most polymers are chemically unreactive and therefore non-biodegradable. Microorganisms cannot break them down, so they persist in the environment for hundreds of years.

Burning plastics produces the greenhouse gas carbon dioxide, and some polymers such as poly(vinylchloride) also release toxic hydrogen chloride gas.

A non-biodegradable material is one that cannot be broken down by microorganisms such as bacteria or decomposers.

Properties of polythene that make it suitable for shopping bags include:

1. Flexible

2. Low density

3. Waterproof

4. Non-toxic

5. Unreactive

Recycling therefore reduces the amount of crude oil used as a raw material and to power industrial processes.

Poly(tetrafluoroethene) is commonly used to make non-stick pans, due to its properties as a polymer.

The three main methods of plastic disposal are landfill, incineration, and recycling.

Fermentation is a process in which sugars dissolved in water are broken down by enzymes in yeast, in the absence of oxygen, to produce ethanol and carbon dioxide.

Fermentation requires a temperature between 15 and 35°C. Below this range the reaction is too slow. Above it, the enzymes in yeast become denatured and stop working.

In fermentation, yeast contains enzymes that convert glucose into ethanol and carbon dioxide.

False.

Fermentation is a batch process. Yeast die when alcohol concentration reaches around 15%, so the vessel must be emptied and the process restarted each time.

Hydration of ethene requires a temperature of around 330°C, a pressure of 60-70 atm, and a concentrated phosphoric acid catalyst.

Acidified potassium dichromate(VI) is a reagent used to test for the presence of an alcohol. A colour change from orange to green is a positive result.

False.

Acidified potassium dichromate(VI) turns from orange to green when added to an alcohol. The reagent starts orange and the colour change indicates oxidation of the alcohol.

Ethanol production by hydration of ethene is a continuous process, whereas fermentation is a batch process.

Bioethanol is ethanol produced from plant material (biomass) via fermentation. It is classified as a biofuel and is considered to be carbon neutral.

Bioethanol is considered carbon neutral because the carbon dioxide absorbed by plants during photosynthesis equals the carbon dioxide released when the bioethanol is burned.

True.

Ethanol is used as a solvent in a range of industries. It can dissolve many substances that water cannot, making it useful in pharmaceuticals, cosmetics, and paints.

Green plants absorb carbon dioxide during photosynthesis and convert it into glucose. This is then fermented to produce bioethanol.

One advantage of bioethanol is that it is renewable (crops can be regrown). One disadvantage is that it has a lower specific energy than fossil fuels, so more is needed to do the same work.

False.

Methanol is poisonous when ingested, even in small amounts. It is used as an industrial solvent and as antifreeze, but must never be consumed.

Two economic impacts of the alcohol industry are:

1. Duties raise over £13 billion per year

2. Exports contribute £6 billion to the economy

However, alcohol misuse costs over £21 billion per year.

Bioethanol production is not truly carbon neutral because it does not account for the carbon dioxide released during harvesting and transporting of the crops.

The hydroxyl group is the -OH functional group present in all alcohols. It is responsible for the characteristic reactions of alcohols.

The general formula of alcohols is C_nH_2n+1OH. Alcohols are named by replacing the final -e of the alkane name with -ol.

The molecular formula of ethanol is C₂H₅OH. Ethanol has 2 carbon atoms, consistent with the general formula C_nH_2n+1OH where n = 2.

Positional isomers are isomers that differ only in the position of a functional group on the carbon chain.

False.

Butan-1-ol and butan-4-ol are the same molecule, just drawn from opposite ends of the chain. By convention, the lowest possible numbers are used, so the correct name is butan-1-ol.

Butan-1-ol and butan-2-ol are positional isomers. They differ in the position of the -OH group: in butan-1-ol the -OH is on carbon 1, and in butan-2-ol it is on carbon 2.

2-methylpropan-1-ol is a chain isomer of butan-1-ol. The longest chain has three carbons and the -OH group is on carbon 1.

False.

The -OH functional group in alcohols is covalently bonded to the carbon chain and is not ionic. The hydroxide ion OH^- carries a negative charge and behaves very differently.

Microbial oxidation is the oxidation of a substance by microorganisms such as bacteria. In alcohols, it converts ethanol into ethanoic acid.

The bacteria responsible for oxidising ethanol to ethanoic acid is Acetobacter. It oxidises the ethanol in the presence of oxygen.

When ethanol is oxidised, ethanoic acid is formed. The equation for this reaction is: C₂H₅OH + 2 [O] → CH₃COOH + H₂O.

[O] represents an oxygen atom from an oxidising agent in an equation. It is a shorthand notation to show that oxidation is occurring without specifying the exact reagent.

[O] represents an oxygen atom from an oxidising agent in an equation. It is a shorthand notation to show that oxidation is occurring without specifying the exact reagent.

True.

When propanol is oxidised by microbial oxidation, the product is propanoic acid. The pattern holds for all primary alcohols: the oxidation product is the corresponding carboxylic acid.

Beer and wine go off when exposed to air because Acetobacter bacteria oxidise the ethanol to ethanoic acid. The sour taste of ethanoic acid makes the drink unpleasant.

When an alcohol is oxidised, the proportion of oxygen in the molecule increases and the proportion of hydrogen decreases.

Infrared spectroscopy is a technique in which infrared light is shone through a substance to identify chemical bonds, because different bonds absorb different wavelengths of infrared light.

The O-H bond in alcohols absorbs infrared radiation in the range 3230-3550 cm^-1.

True.

The C=O bond absorbs at 1680-1750 cm^-1, while the C=C bond (alkenes) absorbs at 1620-1680 cm^-1. The C=O absorption range is at higher wavenumbers.

In infrared spectroscopy, the fingerprint region is a complex part of the spectrum that is unique to each molecule and can be used to identify it.

The O-H absorption in a carboxylic acid occurs at 2500-3000 cm^-1, which is a lower wavenumber range than the O-H absorption in an alcohol at 3230-3550 cm^-1.

In infrared spectroscopy, different chemical bonds absorb different wavelengths of infrared light, producing peaks at characteristic positions on the spectrum.

The C=O bond absorbs infrared radiation in the range 1680-1750 cm^-1.