Poland Szkoła podstawowa, klasa VIII Chemistry
Chapters: 5
1. Hydroxides and acids
Formulas, preparation and uses · Dissociation, indicators and pH
- Acids and Bases: Properties, Indicators and Reactions – An acid gives H⁺ ions in water and a base gives OH⁻ ions. Indicators show which one is present by a colour or smell change, and when H⁺ meets OH⁻ they make water, leaving a salt behind.
- The pH Scale: How Strong Is an Acid or a Base? – pH is a number from 0 to 14 that tells how acidic or basic a solution is. 7 is neutral, below 7 is acidic and above 7 is basic. Each step down means ten times more H⁺ ions.
2. Salts
Neutralisation and naming salts · Making salts and precipitation
- Acids and Bases: Properties, Indicators and Reactions – An acid gives H⁺ ions in water and a base gives OH⁻ ions. Indicators show which one is present by a colour or smell change, and when H⁺ meets OH⁻ they make water, leaving a salt behind.
3. Hydrocarbons
Alkanes · Alkenes, alkynes and polymers · Fossil fuels
- Carbon and Its Compounds: Bonding, Hydrocarbons and Naming – Carbon has 4 outer electrons, so it shares electrons (covalent bonds) instead of gaining or losing them. Because it bonds to itself (catenation) and always makes 4 bonds (tetravalency), it forms millions of compounds: chains, branches and rings, saturated or unsaturated. Compounds with the same functional group form a homologous series that differs by –CH₂–, and IUPAC names are built from the number of carbons + a suffix or prefix for the functional group.
4. Hydrocarbon derivatives
Alcohols · Carboxylic acids and esters
- Chemical Properties of Carbon Compounds, Ethanol and Ethanoic Acid – Carbon compounds burn in oxygen to give CO₂, water, heat and light (combustion); strong oxidising agents turn alcohols into acids (oxidation); unsaturated compounds add hydrogen with a nickel catalyst (addition); saturated compounds swap hydrogen for chlorine in sunlight (substitution). Ethanol reacts with sodium to give hydrogen and dehydrates to ethene; ethanoic acid is a weak acid that makes esters with alcohols and CO₂ with carbonates.
5. Biologically important substances
Fatty acids and fats · Amino acids and proteins · Carbohydrates
- Lipids: Fats, Oils and More – Lipids are biomolecules that do not dissolve in water. The main ones are fats and oils (triglycerides): one glycerol joined to three fatty acids by ester bonds. Saturated fatty acids have straight tails and give solid fats; unsaturated ones have C=C double bonds, bent tails and give liquid oils. Phospholipids build cell membranes and steroids such as cholesterol make hormones.
- Carbohydrates: Classification, Glucose, Disaccharides and Polysaccharides – Carbohydrates are sugars and the big molecules made from sugars. Chemically they are polyhydroxy aldehydes or ketones (many –OH groups plus one C=O), or things that give these on hydrolysis. We sort them by how many sugar units they have: one (monosaccharide), two to ten (oligosaccharide) or many (polysaccharide). Glucose is an aldose with six carbons; fructose is a ketose. Two units join by a glycosidic (–O–) bond to give disaccharides like sucrose, maltose and lactose. Hundreds join to give starch, cellulose and glycogen.