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Year 9 GCSE C2.1 Overview Learning Objectives C2.1.1 Relative formula mass Define ‘relative atomic mass’ and ‘relative formula mass’ Calculate relative formula masses from formulae C2.1.2 Empirical formula Calculate the empirical formula of a compound Calculate relative formula masses from balanced equations C2.1.3 Pure and impure substances Explain what purity means Explain that many useful materials are mixtures Use melting point data to distinguish pure substances from impure substances C2.1.4 Filtration and crystallisation Describe and explain how filtration and crystallisation work C2.1.5 Distillation Describe and explain how simple distillation and fractional distillation work C2.1.6 Chromatography Describe how paper and thin layer chromatography work Calculate Rf values from chromatograms Describe how gas chromatography works C2.1.7 Purification and checking purity Suggest suitable chromatography methods for distinguishing pure from impure substances Suggest suitable purification methods when given information about the substances involved Year 9 GCSE C2.1 Overview C2.1 Keywords Alloy: A mixture of a metal and at least one other element. Balanced chemical equation: A written model for a reaction that shows the formulae and number of units for all the substances involved. Boiling point: The temperature at which a substance changes from the liquid state to the gas state. Carrier gas: An unreactive gas such as nitrogen, or inert gas such as helium, used as the mobile phase in gas chromatography. Chemical formula: A description of a compound or an element that uses symbols to represent the atoms present. Numbers show where there are more than one atom of an element in the substance. Chromatogram: The pattern produced when separating a mixture using chromatography. Chromatography: A separation method that relies on the distribution of a substance between a mobile phase and a stationary phase. Condensed: Turned from the gas state to the liquid state. Condenser: Apparatus that can cool a substance in its gas state to change it to its liquid state. Crystallisation: The process by which crystals are formed during evaporation of a solvent from a solution. Dissolve: The process in which a solute and solvent mix completely to form a solution Empirical formula: Chemical formula showing the simplest whole number ratio of the atoms of each element in a compound. Evaporates: Turns from the liquid state to the gas state. Filtrate: A solution or substance in its liquid state that passes through the filter during filtration. Filtration: The process by which insoluble substances are separated from soluble substances using a filter. Fraction: A substance separated from a mixture during fractional distillation. Fractional distillation: A method used to separate a solvent from a mixture of two or more solvents. Fractionating column: A piece of apparatus used to improve the separation of solvents during fractional distillation. Year 9 GCSE C2.1 Overview Gas chromatography: A type of chromatography that uses silica or alumina packed into a metal tube as the stationary phase, and an unreactive or inert carrier gas as the mobile phase. Impure substances: Material consisting of two or more different elements and/or compounds. Insoluble: Describes a substance that will not dissolve in a given solvent. Melting point: The temperature at which a substance changes from the solid state to the liquid state. Mixture: Material consisting of two or more different substance, not chemically joined together. Paper chromatography: Separation method that uses paper as the stationary phase and a solvent in the liquid state as the mobile phase. Periodic table: A table in which the elements are arranged in rows (periods) and columns (groups), in order of increasing atomic number. Phase: A substance in the solid, liquid, or gas state. Pure substance: Material consisting of just one element or one compound. Purity: A measure of how pure a substance is. A 100% pure substance consists entirely of one element or compound. Relative atomic mass: The mean mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom, defined as 12.0 exactly. Its symbol is Ar. Relative formula mass: The mean mass of a unit of a substance compared to 1/12 the mass of a carbon-12 atom, defined as 12.0 exactly. It is calculated by adding together the relative atomic masses for all the atoms in the formula for the substance. Its symbol is Mr. Relative molecular mass: The mean mass of a molecule of a substance compared to 1/12 the mass of a carbon-12 atom, defined as 12.0 exactly. It is calculated by adding together the relative atomic masses for all the atoms in a molecule. Its symbol is Mr. Residue: Insoluble material left behind in the filter during filtration. Rf values: Relative distance travelled by a substance during chromatography, calculated as: distance travelled by substance ÷ distance travelled by solvent. Saturated solution: A mixture of a solvent and solute that contains the maximum mass of solute at a given temperature Year 9 GCSE C2.1 Overview Simple distillation: A method used to separate a solvent and a solution that have different boiling points. Solubility: A measure of how much solute can dissolve in a given solvent at a certain temperature. Soluble: Describes a substance that will dissolve in a given solvent. Solute: A substance that dissolves in a solvent to form a solution. Solution: A mixture formed when one substance dissolves in another. Solvent: A substance that can dissolve a solute to form a solution. Thin layer chromatography: A type of chromatography that uses silica or alumina spread on a glass or plastic plate as the stationary phase, and a solvent in the liquid state as the mobile phase. Vapour: A substance in its gas state and below its boiling point.