Carbon Compounds, Fuels and Materials: notes

Fuels and Crude Oil

• Fossil fuels are coal, natural gas and petroleum (crude oil). They formed from the remains of ancient plants and animals over millions of years.
• Fractional distillation separates crude oil into fractions by boiling point. Smaller molecules boil off at lower temperatures and are collected higher up the column.
• Alkanes are saturated hydrocarbons with single C-C bonds, such as methane (CH₄) and ethane (C₂H₆). Their general formula is CₙH₂ₙ₊₂.
• Complete combustion of a hydrocarbon in plenty of air gives carbon dioxide and water. Incomplete combustion gives carbon monoxide and soot, which is dangerous.
• Cracking breaks long alkane chains into shorter, more useful alkanes and alkenes. It needs heat and a catalyst.

Alkenes and Addition Reactions

• Alkenes are unsaturated hydrocarbons with at least one C=C double bond, such as ethene (C₂H₄).
• Test for alkenes: bromine water turns from orange-brown to colourless when shaken with an alkene.
• Addition reaction: a small molecule adds across the C=C double bond, leaving a single bond. For example, ethene plus water (with an acid catalyst) gives ethanol.

Alcohols, Acids and Esters

• Alcohols contain the -OH group. Ethanol (C₂H₅OH) is the most common one.
• Fermentation uses yeast to turn sugar into ethanol and carbon dioxide without air. It happens at about 25 to 35 °C.
• Worked calculation: Glucose (C₆H₁₂O₆) ferments as C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.
  • M_r of glucose = 180, M_r of ethanol = 46.
  • 90 g of glucose = 90 ÷ 180 = 0.5 mol.
  • 0.5 mol of glucose gives 1 mol of ethanol = 46 g (theoretical yield).
• Carboxylic acids contain the -COOH group. Ethanoic acid in vinegar is an example.
• Esters form when a carboxylic acid reacts with an alcohol, using an acid catalyst. Many esters smell sweet and fruity.

Polymers, Plastics and Soaps

• Polymers are long chains made of many small units called monomers joined together. Poly(ethene) is made from ethene monomers.
• Plastics disposal: most plastics do not rot, so they stay in landfill and pollute land and water. Burning them releases harmful gases. Recycling is the better option.
• Soaps are made by heating fats or oils with sodium hydroxide. Detergents are synthetic and still clean well in hard water.

Limestone, Cement, Ceramics and Glass

• Limestone is calcium carbonate (CaCO₃). Heating it gives quicklime (CaO) and carbon dioxide.
• Uses of limestone: making cement, iron smelting, and treating acidic soil.
• Cement is made by heating limestone with clay. It is mixed with water, sand and gravel to make concrete.
• Glass is made by melting sand (silicon dioxide), sodium carbonate and limestone.

Zimbabwe's Chemical Industry and the Environment

• Mining provides raw materials such as minerals and chemicals.
• Fertiliser production uses ammonia and nitric acid to make nitrogen-containing fertilisers that help crops grow.
• Sugar production leaves molasses, which can be fermented to make ethanol.
• Environmental effects: sulfur dioxide and nitrogen oxides cause acid rain, carbon dioxide adds to global warming, and factory waste can pollute rivers.

Common Slips

• Do not confuse complete and incomplete combustion. Incomplete combustion produces carbon monoxide, not carbon dioxide.
• Alkanes have single bonds. Alkenes have a double bond.
• Fermentation needs no air and yeast. Do not use "heat" as a main condition.
• Check the functional group: -OH is an alcohol, -COOH is a carboxylic acid.