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THE MEANINGS of CHEMISTRY

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1 THE MEANINGS of CHEMISTRY
S GRADE THE MEANINGS of CHEMISTRY

2 You should learn these as you work through the course.
The following presentation contains the meanings of the terms you need to know in Standard Grade Chemistry. You should learn these as you work through the course. Don’t leave it until the end of the course to try and learn them.

3 Topic 1 CHEMICAL REACTION - a reaction in which a new substance (or new substances) is/are made. ELEMENT - a substance containing only one type of atom. e.g. magnesium is an element because the only atoms in it are magnesium atoms. COMPOUND - a substance made when two or more elements JOIN together. PRECIPITATE - a solid substance that comes out of a solution during a chemical reaction e.g. when carbon dioxide turns lime water milky, the milkiness is a precipitate called calcium carbonate. EXOTHERMIC - a reaction which releases energy . The opposite is ENDOTHERMIC (takes in energy). FILTRATION - using filter paper to separate insoluble from soluble material. FILTRATE - the liquid that passes through filter paper. SOLUBLE - a substance that dissolves. INSOLUBLE - a substance of very low solubility - See SQA data book. DISTILLATION - a purification process involving evaporation, followed by condensation.

4 Topic 2 A CATALYST speeds up a chemical reaction, but is not used up in the reaction, and can be recovered chemically unchanged after the reaction. An ENZYME is a BIOLOGICAL CATALYST (speeds up reactions that take place in living things)) DECOMPOSE means to break up into smaller parts. CONCENTRATION refers to the quantity of dissolved substance in relation to the volume of the solvent.

5 Topic 3 GROUPS - vertical columns of elements in Periodic Table e.g. Group 1 (The Alkali Metals) ALKALI METALS - Group 1 elements (lithium, sodium, potassium, rubidium and caesium) HALOGENS - Group 7 elements (fluorine, chlorine, bromine and iodine) NOBLE GASES - Group 0 elements (helium, neon, argon, krypton, xenon and radon) TRANSITION METALS - The block of metal elements found between Groups 2 and 3 in the Periodic Table (e.g. iron, copper, gold, silver) NUCLEUS - the small centre of every atom. The nucleus contains the positive protons and the neutral neutrons. Virtually all of the mass of the atom is found here. ATOMIC NUMBER - the number of protons in an atom (also equal to the number of electrons in the atom). Atomic number determines where the element is found in the table. MASS NUMBER - The sum of the protons added to the neutrons. ISOTOPES - Atoms with the same atomic number but with a different mass number (Atoms of the same element with a different number of neutrons) IONS - these are atoms after the atom has either lost an electron (or electrons) or gained an electron (or electrons)

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9 Topic 4 BOND - the attraction that holds atoms together
MOLECULE - a small group of atoms joined together (by covalent bonding) DIATOMIC - contains two atoms e.g. O2, CO, N2, Cl2 COVALENT BOND - where two atoms share electrons SINGLE COVALENT BOND - where two electrons are shared DOUBLE COVALENT BOND - where four electrons are shared TRIPLE COVALENT BOND - where six electrons are shared CHEMICAL FORMULA - this gives the number of atoms of each element present in a substance e.g. H2O, C12H22 O11

10 Topic 5 FUEL - a substance which burns releasing energy
COMBUSTION - a reaction of a substance with oxygen, giving out energy EXOTHERMIC - a reaction in which energy is released POLLUTION - substances which damage the environment FRACTIONAL DISTILLATION - separation of a mixture of substances into parts or fractions based the fact that they have different boiling points FLAMMABILITY - refers to how easily a substance burns e.g. a flammable substance burns easily VISCOSITY - describes the thickness of a liquid e.g. a viscous liquid does not run easily. HYDROCARBONS - compounds containing carbon and hydrogen only INCOMPLETE COMBUSTION - when there is insufficient oxygen for a fuel to burn completely. CATALYTIC CONVERTER - a device on cars, containing a transition metal such as platinum, which converts harmful gases such as carbon monoxide and nitrogen oxides into less harmful gases. LEAN BURN ENGINE - one which uses more air and less fuel than non-lean burn engines

11 Topic 6 (I) ALKANE - a member of the family of hydrocarbons of general formula CnH2n+2 HOMOLOGOUS SERIES - a family of compounds with similar chemical properties. All members of the family fit the same general formula e.g. the ALKANES are a homologous series with the general formula CnH2n+2 CYCLOALKANES - a homologous series of hydrocarbons of general formula CnH2n where the carbon atoms are joined into a circular arrangement ISOMERS - compounds with the same molecular formula but with a different structural formula ALKENES - a homologous series of hydrocarbons of general formula CnH2n where there is a double bond between two of the carbon atoms

12 Topic 6 (II) SATURATED - where the carbon atoms are only joined by single covalent bonds e.g. alkanes UNSATURATED - where two of the carbon atoms are joined by a double covalent bond e.g. alkenes ADDITION REACTION - a reaction where a substance adds onto an unsaturated compound to give only one product. If the starting substance is an alkene, the product will be saturated. CRACKING - where a long chain alkane is broken into a mixture of a short chain alkane and an alkene. These molecules are smaller and more useful. A catalyst is needed to speed up the reaction and reduce the heat required.

13 Topic 7 METAL ELEMENTS - conduct electricity when solid and when molten. The type of charged particle which carries the current in a metal is called an electron. NON-METAL ELEMENTS - do not conduct electricity, with the exception of solid carbon in the form of graphite. Compounds containing metals are called ionic compounds. Ionic compounds do not conduct electricity when solid because the ions are not free to move Ionic compounds conduct electricity when their ions are free to move about (molten or in solution). Such compounds are called electrolytes (contain ions which can move about). The purpose of an electrolyte is to complete the circuit. COVALENT MOLECULES – small group of non-metal atoms with low melting/boiling points. COVALENT NETWORKS - very high melting/boiling point network of non-metal atoms. ELECTROLYSIS – using electricity to split up an ionic compound. D.C SUPPLY – is used so that the products at each electrode can be identified.

14 Topic 8 NON METAL ELEMENTS - can react with air or oxygen to form compounds called oxides. NON-METAL OXIDES - dissolve in water produce acids e.g. CO2, NO2, SO2, SO3. SO2 and NO2 react with water to form acid rain. Oxides of non-metals which do not dissolve do not affect the pH. OXIDES OF METALS OR HYDROXIDES of metals which dissolve in water produce alkaline solutions. The data book gives information about which ones dissolve or react. The oxides of Group 1 metals and some of some Group 2 metals produce alkaline solutions with water. ACIDS have a pH of less than 7. (pH<7) ALKALIS have a pH of more than 7. (pH>7) Pure water and neutral solutions have a pH equal to 7. (pH=7) All acid solutions contain HYDROGEN IONS (H+ (aq)) and have pH values < 7. If an electric current is passed through any acid solution, the H+ ions are changed into hydrogen gas at the negative electrode. Hydrogen gas burns with a pop.

15 Topic 8 All alkaline solutions contain HYDROXIDE IONS (OH- (aq)) and have pH values > 7 Water has a very low concentration of ions In water and any neutral solution, the concentration of H+ ions and OH- ions is the same and this gives a pH = 7 (neutral). In an acid solution the concentration of hydrogen ions (H+(aq)) is more than that in pure water. In an alkaline solution the concentration of hydroxide ions (OH-(aq)) is more than that in pure water. DILUTING ACIDS AND ALKALIS Adding more water to an acid increases the pH of the solution towards 7 making it less acidic. (The acidity decreases and the pH value increases). Adding more water to an alkali decreases the pH of the solution towards 7 making it less alkaline. (The alkalinity decreases and the pH value decreases). NB In both cases, the pH number moves towards 7 Diluting an acid decreases the concentration H+(aq) ions. Diluting an alkali decreases the concentration OH- (aq) ions.

16 Topic 9 NEUTRALISATION is the reaction of acids with neutralisers and at the same time the pH value moves towards 7. REACTIONS OF ACIDS WITH NEUTRALISERS (EXAMPLES OF NEUTRALISATION) Acid + Alkali > Salt + Water Acid + Metal Oxide > Salt + Water Acid + Metal Carbonate -> Salt + Water + Carbon dioxide Acid + Metal > Salt + Hydrogen Some metals such as copper, silver and gold do not react with dilute acids. WHAT IS A SALT? A salt is a substance in which the hydrogen ion of an acid has been replaced by a metal ion (or the ammonium ion). When an acid is neutralised by an alkali, H+ ions from the acid join with OH- from the alkali to form water. A BASE is a substance which neutralises an acid. This means that alkalis (metal hydroxides), metal oxides, metal carbonates and metals are all examples of bases. An alkali is made if the base dissolves in water.

17 Topic 9 Pb(NO3)2(aq) + 2NaI(aq) -------> PbI2(s) + 2NaNO3(aq)
NAMING SALTS Hydrochloric acid (HCl) always makes CHLORIDE salts Nitric acid (HNO3) always makes NITRATE salts Sulphuric acid (H2SO4) always makes SULPHATE salts SOLUBLE SALTS - add excess of an insoluble metal oxide or metal carbonate to an acid, and remove the unreacted substance by filtration, followed by evaporation of the filtrate to obtain the salt. INSOLUBLE SALTS - can be formed by precipitation. To make insoluble lead (II) iodide, mix together two separate solutions of soluble salts one containing lead (II) ions and the other containing iodide ions e.g. lead (II) nitrate solution and sodium iodide solution. Pb(NO3)2(aq) + 2NaI(aq) > PbI2(s) + 2NaNO3(aq) Lead iodide is formed as a yellow precipitate which can be removed easily by filtering PRECIPITATION is the reaction of two solutions to form an insoluble product called a precipitate. The data book indicates the solubility of many substances.

18 Topic 10 BATTERY - a device containing chemicals that react to produce electricity. Advantage of battery over mains is it is safer and portable. A disadvantage is that it is more expensive than mains electricity. A battery runs out because the chemical reaction stops/chemicals are used up. CELL - the correct term for devices called batteries. ELECTROLYTE - a substance that contains ions which can move (either molten ionic compounds or ionic compounds in solution or a watery paste as in a dry cell). RECHARGEABLE b - a cell in which electricity can regenerate chemicals to allow the cell to produce electricity many times. VOLTAGE - a measure of the push of electrons between two reactions. ELECTROCHEMICAL SERIES - a list of reactions in the data book (page 7) which can be used to determine which reaction of a pair is better at pushing electrons onto the other reaction. Electrons flow from the higher equation to the lower equation. The further the equations from each other the higher the voltage.

19 Topic 10 DISPLACEMENT REACTION - where one metal higher in the electrochemical series displaces (pushes out) another metal from a solution of the other metal. ION BRIDGE – (salt bridge) a link containing ions which completes a circuit. OXIDATION - the reaction of a metal element to form a compound. OXIDATION - the loss of electrons by a reactant in any reaction. REDUCTION - the reaction of a compound to form a metal. REDUCTION - the gain of electrons by a reactant in any reaction. REDOX REACTION - a reaction in which reduction and oxidation occur together. OILRIG - This will help you remember oxidation and reduction. OIL stands for Oxidation Is the Loss (of electrons). RIG stands for Reduction Is the Gain (of electrons).

20 Topic 11 DENSITY - the mass of a metal divided by the space it takes up. A metal is dense because the atoms are packed closely together and take up little space. MALLEABILITY - the ability of a metal to be beaten into shape. CONDUCTIVITY - the ability of a substance to let heat or electricity through it. ORE - a naturally-occurring compound of metals. ELECTROLYSIS - splitting an ionic substance into its elements using electricity. REDUCTION - a reaction is which a metal is obtained from a compound. ALLOY - a mixture of metals with non-metals.

21 Topic 12 CORROSION - the changing of the surface of a metal when it loses electrons. RUSTING - the special name for the corrosion of iron FERROXYL INDICATOR - turns blue in the presence of iron(II) ions Fe2+(aq) FERROXYL INDICATOR - turns pink in the presence of hydroxide ions PHYSICAL PROTECTION - stopping corrosion by keeping out air and/or water CHEMICAL PROTECTION - using more reactive metals to push electrons onto iron GALVANISING - coating iron with a layer of zinc TIN PLATING - coating iron with a layer of tin ELECTROPLATING - coating a metal with a layer of another metal using electricity SACRIFICIAL PROTECTION - where a more reactive metal sacrifices itself to protect the less reactive metal

22 Topic 13 PLASTICS - a wide variety of large molecules made from products from crude oil distillation SYNTHETIC – made by the chemical industry FIBRE - a large molecule which is made into long threads NATURAL - occurring in nature BIODEGRADABLE - broken down into smaller pieces by living organisms TOXIC - harmful THERMOPLASTIC - a plastic that can be re-softened by heating e.g. poly(ethene) THERMOSETTING - a plastic that cannot be re- softened by heating e.g. bakelite MONOMER - small units that join together to give a very big molecule POLYMERS - very big units made when many monomer molecules join together POLYMERISATION - the process in which monomers join to give a polymer CRACKING - a reaction in which long-chain hydrocarbons are converted into unsaturated hydrocarbons ADDITION POLYMERISATION - the making of a polymer by a series of addition reactions

23 Topic 14 NUTRIENTS - soluble compounds containing nitrogen, phosphorus and potassium which are absorbed by roots. NPK FERTILISERS - those containing Nitrogen, Phosphorus and Potassium NITRIFYING BACTERIA - bacteria living in swellings on the roots of pea and bean plants (legumes) that can take nitrogen out of the air and give this to plants. FIXING NITROGEN - taking nitrogen out of the air and changing it into useful compounds for plants e.g. nitrates. DENITRIFYING BACTERIA - taking nitrates out of soil and changing it nitrogen. HABER PROCESS - the joining of nitrogen and hydrogen gases to make ammonia gas using an iron catalyst. OSTWALD PROCESS - the oxidation of ammonia with oxygen to make nitrogen dioxide using a platinum catalyst. The nitrogen dioxide dissolves in water to produce nitric acid. The industrial manufacture of nitric acid. The Ostwald process is exothermic. EXOTHERMIC REACTION - a reaction which gives out energy.

24 Topic 15 I PHOTOSYNTHESIS - a process in plants in which carbon dioxide and water are changed into carbohydrates and oxygen with the help of sunlight and chlorophyll. CARBOHYDRATE - a compound containing carbon, hydrogen and oxygen in which the ratio of hydrogen:oxygen is the same as in water i.e. 2:1 ENDOTHERMIC - a reaction in which energy is absorbed (or taken in). CHLOROPHYLL - a green chemical in the leaves of plants which is able to trap the energy of the sun and use this energy to make carbohydrates. RESPIRATION - a process in living things where oxygen is used to break up food and produce water, carbon dioxide and energy ISOMERS - compounds with the same molecular formula but with a different structural formula. MONSACCHARIDE - single sugar molecules such as glucose or fructose (C6H12O6) DISACCHARIDE - two sugar molecules joined together as in sucrose or maltose (C12H22O11)

25 Topic 15 - II CONDENSATION - the joining of sugar molecules with the elimination of water molecules. POLYMERISATION - the joining of many sugar molecules together e.g. when glucose is changed into starch. DIGESTION - a process in living things where large molecules are broken into smaller molecules with the help of enzymes. ENZYMES - biological catalysts which are used to help reactions such as photosynthesis and digestion in living things. HYDROLYSIS - the breakdown of molecules by splitting them with water e.g. sucrose into molecules of glucose and fructose. FERMENTATION - a reaction between sugars and enzymes in yeast which produces alcohol and carbon dioxide. ALKANOL (alcohol) - a compound made by the fermentation of a carbohydrate (e.g. ethanol). ETHANOL - a member of the alkanol family with formula C2H5OH.

26 Chemical Tests CARBON DIOXIDE –turns lime water milky
HYDROGEN GAS – burns with a pop OXYGEN GAS – relights a glowing splint ALKENES C=C – decolourises Bromine solution GLUCOSE/FRUCTOSE/MALTOSE – turn Benedict’s solution brick red STARCH – turns iodine solution blue/black IRON (ll) IONS Fe2+ - turn ferroxyl solution blue ACIDS – turn universal indicator red/orange pH less than 7 ALKALIS – turn universal indicator blue/purple pH greater than 7 NEUTRAL SOLUTIONS – turn universal indicator green pH = 7 AMMONIA – turns pH paper/universal indicator blue/pH greater than 7/alkaline.


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