Chemical Quantities

Elements are the simplest chemicals - they cannot be broken down into simpler chemicals.Compounds are chemicals containing two or more elements chemically combined together.An atom is the smallest particle of an element.A molecule is a particle containing two or more atoms joined together chemically.An ion is an atom, or group of atoms, which has become electrically charged by the loss or gain of one or more electrons.Symbols are used to represent elements, e.g. Fe for iron and C for carbon.Formulae are used to represent compounds e.g. H20 for water and NaCl for sodium chloride.A molecular formula shows the numbers of atoms of the different elements in one molecule of a compound, e.g. CH4 for methane and C2H6 for ethane.An empirical formula shows the simplest whole number ratio of the different atoms of different elements in a compound, e.g. CH4 for methane and CH3 for ethane.A balanced chemical equation describes a chemical reaction using symbols for the reactants and products. The numbers of each kind of atom are the same on both sides of the equation.Thermal decomposition is the breaking up of substances into simpler substances by heating.Spectator ions are ions which take no part in a reaction.Acids are substances which donate hydrogen ions, H+ (protons).Bases are substances which accept hydrogen ions, H+ (protons).Alkalis are soluble bases.Neutralisation occurs when H+ ions react with OH- or O2- ions forming water.Salts are ionic compounds formed when an acid reacts with a base. Most salts are metal/non-metal compounds.The relative molecular mass of an element or compound is the sum of the relative atomic masses of all the atoms in its molecular formula.The relative formula mass of a compound is the sum of the relative atomic masses of all the atoms in its formula.Molar mass is the mass of one mole of a chemical - the unit is g mol-1. As always with molar amounts, the symbol or formula of the chemical must be specified.The molar volume of a gas is the volume of 1 mole. At room temperature and atmospheric pressure, the molar volume of all gases is 24 dm3 mol-1.Concentration/g dm-3 = ( mass of solute/g ) / ( volume of solution/dm3).Concentration/mol dm-3 = ( amount of solute/mol ) / ( volume of solution/dm3).The actual yield is the mass of product obtained.The theoretical yield is the mass of product obtained if the reaction goes according to the equation.The percentage yield = (( actual yield ) / ( theoretical yield )) x 100A limiting reactant is a substance which is present in an amount which limits the theoretical yield. Often, some reactants are added in excess to ensure that the most valuable reactant is converted to as much product as possible.Atom economy = (( mass of atoms in desired product) / (mass of atoms in all reactants)) x 100

Analysis of 20.1 g of iron bromide showed that it contained 3.8 g of iron and 16.3 g of bromine What is its formula? Iron BromineCombined masses 3.8 16.3 Molar mass 55.8 79.9Combined moles 3.8 / 55.8 16.3 / 79.9of atoms = 0.068 = 0.204Ratio of combined 0.068/0.068 0.204/0.068atoms = 1 = 3Simplest ratio 1 : 3So, the empirical formula is FeBr3.

What mass of iron can be obtained from 1 kg of iron (III) oxide ( iron ore ) ?Fe2O3 (s) + 3CO (g) ----> 2Fe (s) + 3CO2 (g)1 mol Fe2O3 ----> 2 mol FeM(Fe2O3) = ( 2 x 55.8 g mol^-1) + ( 3 x 16.0 g mol^-1) = 111.6 + 48.0 =159.6 g mol^-1So, 159.6 g Fe2O3 ----> 2 x 55.8 g Fe = 111.6 g Fe159.6 g Fe2O3 ----> 111.6 g Fe1 g Fe203 ----> 111.6 / 159.6 = 0.7 g Fe1 kg of iron (III) oxide produces 0.7 kg of iron.

What volume of oxygen reacts with 60 cm^3 methane and what volume of carbon dioxide is produced if all volumes are measured at the same temperature and pressure?CH4 (g) + 2O2 (g) ----> CO2 (g) + 2H20 (l)1 mol 2 mol 1 mol insignificant volume 1 volume 2 volume 1 volume of liquid below 100CSo, 60 cm^3 methane reacts with 120 cm^3 oxygen to produce 60 cm^3 carbon dioxide.

A car battery contains 2354.4 g of sulphuric acid ( H2SO4 ) in 6 dm^3 of the battery liquid. What is the concentration of sulphuric acid in g dm^-3 and mol dm^-3 ?Concentration/g dm^-3 = 2354.4 / 6 = 392.4 g dm^-3M(H2SO4) = 98.1 g mol^-1So, amount of H2SO4 in the battery = 2354.4 / 98.1 = 24 molConcentration = 24 / 6 = 4 mol dm^-3

A sample of tap water contains 0.15 mg of Fe^3+ per dm^3. What is its concentration in ppm ? ( Assume that 1 cm^3 of tap water has a mass of 1.0 g )0.15 mg of Fe^3+ in 1 dm^3 solution = 0.15 / 1000 = 0.00015 g Fe^3+ in 1000 g solutionConcentration/ppm = ( 0.00015 / 1000 ) x 10^6 = 0.15

A modern gas - fuelled lime kiln produces 500 kg of calcium oxide, CaO (quicklime), from 1000 kg of crushed calcium carbonate, CaCO3 (limestone). What is the percentage yield of calcium oxide ?CaCO3 (s) ----> CaO (s) + CO2 (g)From the equation: 1 mole CaCO3 ----> 1 mole CaO[40.1 + 12 + (3 x 15)] g CaCO3 ----> (40.1 + 16) g CaO100.1 g CaCO3 ----> 56.1 g CaCOSo, 1 g CaCO3 ----> ( 56.1 / 100.1 ) g CaOTheoretical yield from 1000 kg CaCO3 = ( 56.1 / 100.1 ) x 1000 kg CaO = 560.4 kgThe actual yield of CaO = 500 kg CaOPercentage yield = ( 500 / 560.4 ) x 100 = 89 %

Titanium is manufactured by heating titanium (IV) chloride with magnesium:TiCl4 (g) + 2Mg (l) ----> Ti (s) + 2MgCl2 (s)What is the atom economy of this process?Relative mass of reactants = Mr(TiCl4) + 2Ar(Mg) = Ar(Ti) + 4Ar(Cl) + 2Ar(Mg)= 47.9 + 142 + 48.6 = 238.5Relative mass of desired product = Ar(Ti) = 47.9Atom economy = ( 47.9 / 238.5 ) x 100 = 20.1 %