STANDARD GRADE CHEMISTRY : GENERAL LEVEL NEED TO KNOW SHEETS (BASED ON 1998 2006 EXAMS) TOPIC NO 1 -ide means two elements only ate/-ite means two elements + oxygen a solution contains a solid (solute) dissolved in a liquid (solvent) 2 only one thing can be changed in a fair test a catalyst speeds up a chemical reaction and remains the same weight after the reaction. 3 the test for oxygen is that it relights a glowing splint. oxygen makes up 20% of the Earth s atmosphere. the test for hydrogen is that it burns with a pop. All the elements in the same Group, (column) have similar properties and have the same number of outer electrons (No of electrons on Page 1 of Data Book). Non-metals occur on the right hand side of the Periodic Table. Group 1 is the Alkali metals (very reactive so stored under oil). The Transition metals are between Groups 2 and 3. Group 7 is the Halogens. Group 0 is the Noble Gases (very unreactive). Atoms are neutral because the number of protons (+) = number of electrons (-) Carbon (in the form of graphite) is the only non-metal conductor (all metals conduct). A molecule contains two or more atoms joined together. The centre of an atom (which holds the protons) is called the nucleus. The electron arrangement of each element is on page 1 of the Data Book. 4 Diatomic elements contain two atoms in their molecule (remembered by CHINFOB ). Monatomic elements have only one. A covalent bond occurs between two non-metals.
5 a fossil fuel has been made over millions of years from dead plants or animals (coal, oil, gas). Fossil fuels are finite resources (they will run out in future). crude oil is made into useful products by fractional distillation. when fuels burn they need oxygen and make water plus carbon dioxide. Hydrogen burns to make water only. the test for carbon dioxide is that it turns lime water milky. The order of boiling points/viscosities (lowest first) is petrol/kerosine/diesel. Road tar (bitumen) is made from the residue fraction. when a fuel burns incompletely, soot (carbon) or carbon monoxide (poisonous) are made. Cars have lean burn engines (increase the amount of air) and catalytic converters (contain platinum) to turn harmful gases into harmless ones. 6 a hydrocarbon contains hydrogen and carbon. the number of carbons is given by a rhyme or can be worked out from page 6 of the Data Book. alkanes contain single carbon to carbon bonds only. alkenes contain one double carbon to carbon bond. cycloalkanes join themselves head to tail. alkenes are said to be unsaturated (double bond) whereas alkanes and cycloalkanes) are saturated. the test for unsaturation (alkenes) is that it decolourises bromine solution (in an addition reaction). for example the molecular formula for propane is C 3 H 8 The structural formula is H H H H - C - C - C - H H H H and the shortened structural formula is CH 3 CH 2 CH 3. Learn how to write these for other alkanes/alkenes. cracking uses heat and a catalyst to break a longer molecule into shorter, more useful ones eg C 8 H 18 C 2 H 4 + C 6 H 14 the general formula for alkanes is C n H 2n+2 the general formula for cycloalkanes and alkenes is C n H 2n
13 synthetic means man-made. plastics are made from hydrocarbons called alkenes. a synthetic substance is a man-made one. plastics are non-biodegradable. a thermoplastic melts when heated, a thermoset does not. three monomers (single unit molecules) can be joined by opening up their double bonds to form a polymer (long chain molecule). H H H H H H H H H H H H C = C C = C C = C - C - C - C - C - C - C - H H H H H H H H H H H H polymers are named by placing poly in front of the monomers name. the test for carbon dioxide is that it turns lime water milky. 15 a carbohydrate contains carbon, hydrogen and oxygen. photosynthesis occurs when plants take in carbon dioxide and water and make oxygen and glucose. the green material in plants that traps light is called chlorophyll. the test for glucose is that it turns hot Benedict s orange. the test for starch is that it turns iodine blue/black. respiration produces carbon dioxide and water. fermentation occurs when glucose is turned into alcohol (ethanol) by yeast. Carbon dioxide gas is also given off. Distillation is used to separate the alcohol from the water. when glucose molecules join up to form starch it is condensation polymerisation. 7 electrolysis is when a compound is split up using electricity. in electrolysis, metals (positively charged) are attracted to the negative and non-metals (negatively charged) are attracted to the positive. Ionic compounds (eg copper chloride) only conduct when molten or in solution because the ions become free to move (ie an electrolyte) Covalent compounds contain non-metals only. Covalent compounds do not conduct electricity.
8 ph ranges from 1 to 14; 1 is strong acid, 7 is neutral and 14 is strong alkali. all acids contain H + ions; all alkalis contain OH - ions (hydroxide). common neutralisers of acids include farmer s lime, milk of magnesia, sodium hydrogen carbonate (baking soda). acid rain is caused by sulphur dioxide (from sulphur in fuels) and nitrogen oxides. when water is added to acids or alkalis, the ph moves towards 7. the three common acids are hydrochloric (HCl), nitric (HNO 3 ) and sulphuric (H 2 SO 4 ). 9 an acid is neutralised by a base (ie alkalis, metal oxides or carbonates) to make a salt + water. an acid reacts with a carbonate to also give off carbon dioxide gas. acids react with MAZIT metals (magnesium, aluminium, zinc, iron, tin) to give off hydrogen gas. when an acid reacts with excess metal oxide or carbonate, the residue is the excess oxide or carbonate and the solution is the salt. An acid conducts electricity giving off hydrogen at the negative. ionic compounds react by swapping partners. 10 a battery s advantage over mains is that it is portable. the electrolyte in a car battery is sulphuric acid. a battery runs out when the chemicals get used up. the further apart metals are in the league table (on page 7 of the Data Book) the bigger is the voltage. a chemical cell is made from two different metals and an electrolyte. electrons flow from the more to the less reactive metal (along wires). 11 the order of reactivity of the metals is given on page 7 of the Data book. metals are strong and good conductors of heat and electricity. only the very reactive metals (like sodium and potassium) react with water to give hydrogen. only the MAZIT metals (magnesium, aluminium, zinc, iron and tin) react with acids to give hydrogen gas.
12 iron is the metal made in the Blast furnace. an alloy is a mixture of two metals eg brass. both oxygen (air) and water are necessary for rusting. salt speeds up rusting. when iron rusts it turns into Fe 2+ (which turns ferroxyl blue) iron is protected from corrosion by attaching it to a more reactive metal (sacrificial protection) or the negative terminal of a power supply (cathodic protection) the metal used to galvanise iron is zinc. 14 the gases of the air that combine in a lightning storm are nitrogen and oxygen. the essential elements plants need in fertilisers are nitrogen, phosphorus and potassium (N, P, K). nitrogen occurs in the ammonium ion (NH 4 + ) peas, beans and clover all contain root nodules in which they make their own fertiliser. fertilisers are made by the Haber Process where nitrogen and hydrogen join to make ammonia using an iron catalyst. nitrate fertilisers are made by the Ostwald Process (ammonia is turned into nitric acid using a platinum catalyst). Fertilisers must be soluble in water to be taken up by plants.