IGCSE Chemistry

Word equations have just the names of the reactants and products involved: Hydrogen + Oxygen > Water H + O > H 2 O ^ 1 oxygen and 1 hydrogen on the left and on the right 2 hydrogen and 1 oxygen -> not balanced Balanced equations are the symbols of the products and reactants including the numbers of each, there must be an equal number of each element on both sides of the equation, if there are not you can alter this by putting the right number in front of a symbol: 2H + O > H2O ^2 hydrogens and 1 oxygen on both sides State symbols: In balanced equations these state symbols go after a element or compound to show what state it is in (S) solid (L) liquid (G) gas (Aq) aqueous/ solid dissolved in liquid

At standard temperature and pressure, one mole of any gas will occupy 24000 cm3; also known as 24dm3. Calculating molar volume from mass Example: 976 cm 3 of oxygen was found to have a mass of 1.3 g Calculate the molar volume of oxygen, under these conditions. Volume = mass x no. of moles Mass of oxygen, O 2 , = 32.0 g. Volume of 1 g = 976 ÷ 1.3 Hence, 32 g = (976 ÷ 1.3) × 32 = 24024 cm 3 Answer: 24.0 is the volume of 32.0 g of O 2 .

Calculating Molecular Formula 1 Write the element symbols S O 2  Write the masses or the % of the elements  3.2 g 6.4 g – 3.2 g = 3.2 g 3  Write the A r values of each element 32 16 4  Divide masses by At   3.2 ÷ 32 = 0.1 3.2 ÷ 16 = 0.2 5 Divide by the smallest number 0.1 ÷ 0.1 = 1 0.2 ÷ 0.1 = 2 6 Write the formula SO 2 Calculating Molecular Formula From the empirical formula, you can work out the molecular formula from the relative formula mass (M r ) of the compound. Add up the atomic masses of the atoms in the empirical formula. For example, the empirical formula of a hydrocarbon is CH 2 and its M r is 42. The mass of the atoms in the empirical formula is 14 42 ÷ 14 = 3 so you need to multiply the numbers in the empirical formula by 3 The molecular formula of the hydrocarbon is therefore C 3 H 6 .

Empirical formula - It is the formula that represents the simplest whole number ratio of the atoms of each element present in a compound. Molecular formula - The molecular formula gives the actual number of atoms of each element in one molecule of the compound.

It is not always possible to get the calculated amount of product in a reaction The percentage yield can be calculated: The actual yield is the mass of the product made when the reaction is carried our for real. The theoretical yield is the maximum mass of the product of the reactants. To calculate theoretical yield: 1. Use molar mass of reactant to convert grams of reactant to moles of reactant 2. Use the mole ratio between reactant and product to convert moles reactant to moles product 3. Use the molar mass of the product to convert moles product to grams of product A 100% yield means it all reacted and no product has been lost Loss may occur in: Filtering Evaporating Transferring liquids Not all reactants react to make the product

Reactivity Series Reactions to remember: Metal + Water --> Metal hydroxide + hydrogen Metal + hydrochloric acid --> metal chlride + hydrogen Metal + sulphuric acid --> metal sulphate + hydrogen Displacement Reactions A more reactive metal is able to displace a less reactive metal from its solution e.g. Magnesium + iron sulphate --> magnesium sulphate + iron                Mg      +     FeSO4       -->        MgSO4              +  Fe Series Potassium                                                               ** Really reactive metals are found in compounds Sodium Lithium Magnesium Aluminium Carb...

Isotopes Isotopes - atoms of the same element with the same atomic number but different masses E.g. Isotopes of carbon Isotopes do not differ chemically (same no. of electrons). However physical properties may vary due to different mass numbers. (different no. of neutrons) Working out Ar from Isotopes abundances  Ar = relative atomic mass Ar is a weighted average, it is worked out using the abundance of each isotope. e.g. Chlorine has 2 isotopes (Cl 35 and Cl 37) 75% = Cl35 25% = Cl37 Calculation (35 x 75%) + (37 x 25%) = 35.5

A mole is that amount of substance that contains 6.02 x 10 23 atoms, molecules etc. This number is known as the Avogadro constant Molar masses A mole of an element will have a mass equal to its Ar but in grams A mole of a compound will have a mass equal to its Mr but in grams Moles tell you how many particles are present, and the ratio of moles tells you the ratio of particles that are represented by an equation.  You can find out how many moles are present by dividing the mass by the Mr: number of moles = mass ÷ Mr                                      

Oxidization  Metals and metal oxides  Example  Magnesium + copper oxide --> magnesium oxide + copper Magnesium has been  oxidized to magnesium oxide   Copper has been reduced to copper Copper oxide is the oxidizing agent - it oxidizes but gets reduced in the process Mg is the reducing agent - it reduces the CuO to Cu but gets oxidized in the process e.g. Ca + ZnO --> CaO + Zn

Isotopes are atoms of the same element that have different number of neutrons (% of isotope 1 × mass of isotope 1) + (% of isotope 2 × mass of isotope 2) ÷ 100 In the case of chlorine: (75 × 35) + (25 × 37) ∕ 100 = 35.5 The relative atomic mass of an element is the average value for the isotopes of the element. It takes into account the percentage abundance of isotopes.

Atomic number - the number of protons in the nucleus of an atom, which determines the chemical properties of an element and its place in the periodic table. Mass number - the total number of protons and neutrons in a nucleus. The larger number shown on the periodic table.  Isotopes - each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass. Relative atomic mass (Ar) - the mass of an atom of a chemical element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom (the mass number). 

States of matter: Solid - Difficult to compress - Fixed shape - Fixed volume  - Particles are closely packed Liquid - Molds shape to container  - Fixed volume  - Cannot be compressed  - Particles far apart  Gas - Particles far apart - No fixed shape - No fixed volume  - Easy to compress 

Definitions: Solvent - dissolves other substances Solute - dissolved in other substance Solution - liquid mixture where the solute has dissolved Saturated Solution - a solution that has reached maximum concentration

Separation Techniques: Filtration: Consists of a barrier that one component of the mixture cannot pass through e.g. water goes through rocks are caught Distillation  One substance is evaporated off, the other is left in the flask e.g. salt water is heated, water evaporates, salt is left Fractional distillation  The mixture is evaporated and rises up the tube. Different substances have different boiling points and so will evaporate at different times. As mixtures travel up the tube they condense and are collected. e.g. different liquids Crystallization A solution is heated allowing the solvent to evaporate, the solute is left behind. e.g. salt dissolved in water Chromatography Chromatography paper is placed in a solvent, different substances are placed on the paper, the different components of the substances will travel to different places.

Chromatography RF = Distance from baseline to spot/distance from baseline to solvent front Solvent front - point at which water stopped moving up to paper Spot - the point where a bond or spot of colour is Baseline - where the original sample was placed Pencil not pen pen ink will bleed in water and ruin results

The Periodic Table: Group number - how many electrons are in the outer shell Period number - how many occupied shells there are Atom - Smallest part of something Molecule - smallest unit of a compound ATOMS All atoms are made up of protons electrons and neutrons, these are known as subatomic particles. Every element is represented by a chemical symbol e.g. Mass number = protons + neutrons Atomic number = protons (equal to electrons) Particle Relative mass Charge Proton 1 +1 Neutron 1 - Electron 1/2000 -1

The arrangement of electrons: Electrons orbit the nucleus They are arranged in regions called 'shells' which are positioned a fixed distance from the nucleus. First shell - 2 electrons Second shell - 8 electrons Third shell - 8 electrons Group no. = electrons in outer shell Period no. = no. of occupied shells Electronic Configuration  e.g.  2,1  2,7