GCSE Combined Science Chemistry key terms and definitions
104 Chemistry terms with their meanings, in alphabetical order. Each comes from a Yumio Chemistry lesson, and links to the topic where it is taught.
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- Accurate
- Close to the true value. Required practicals and working scientifically in chemistry
- Alloy
- A mixture of a metal with at least one other element, usually harder than the pure metal. Corrosion, alloys and materials
- Anode
- The positive electrode, where negative ions lose electrons. Electrolysis
- Anomalous result
- A result that does not fit the pattern of the others. Required practicals and working scientifically in chemistry
- Atmosphere
- The layer of gases around the Earth. The Earth's atmosphere, past and present
- Atom economy
- The percentage of the mass of the reactants that ends up in the useful product. Percentage yield and atom economy
- Avogadro constant
- The number of particles in one mole: 6.02 × 10²³ per mole. The mole and reacting masses
- Balancing numbers
- The big numbers in front of formulae in an equation. They give the ratio of moles. The mole and reacting masses
- Bauxite
- The ore from which aluminium oxide is obtained. Extracting metals by electrolysis
- Bioleaching
- Using bacteria to produce a solution that contains metal compounds from low-grade ore. Life cycle assessments, recycling and getting metals sustainably
- Bleach
- To remove the colour from something. Chlorine bleaches damp litmus paper white. Tests for gases
- Brine
- Concentrated sodium chloride solution. Electrolysis of aqueous solutions
- Burette
- A long tube with a tap that delivers a measured volume of solution. Titrations and their calculations
- Carbon footprint
- The total amount of carbon dioxide and other greenhouse gases given out over the full life cycle of a product, service or event. Greenhouse gases, climate change and air pollution
- Catalyst
- A substance that speeds up a reaction and is not used up. Tests for gases
- Cathode
- The negative electrode, where positive ions gain electrons. Electrolysis
- Chromatography
- A method of separating a mixture of soluble substances by letting a solvent move through it on a stationary phase. Purity, formulations and chromatography
- Climate change
- A long-term change in the Earth's weather patterns, linked to a rise in average global temperature. Greenhouse gases, climate change and air pollution
- Closed system
- A system in which nothing can enter or leave. Reversible reactions and equilibrium
- Composite
- A material made of a reinforcement embedded in a matrix or binder. Corrosion, alloys and materials
- Compromise
- A condition chosen between two competing needs, such as a good yield and a fast rate. Equilibrium: predicting shifts and the Haber compromise
- Concentration
- The amount of solute dissolved in a given volume of solution. Concentration and limiting reactants
- Concordant
- Titration results within 0.10 cm³ of each other. Exam calculations: moles, solutions, titration and yield
- Condense
- Change from a gas to a liquid. The Earth's atmosphere, past and present
- Control variable
- A variable you keep the same to make the test fair. Required practicals and working scientifically in chemistry
- Corrosion
- The destruction of a metal by reaction with substances in the environment. Corrosion, alloys and materials
- Cryolite
- A compound that dissolves aluminium oxide and lowers the temperature needed to melt it. Electrolysis
- Decomposition
- A reaction in which one compound breaks down into simpler substances. Extracting metals by electrolysis
- Dependent variable
- The variable you measure in an investigation. Required practicals and working scientifically in chemistry
- Desalination
- Removing salt from sea water to make fresh water. Earth's resources, potable water and waste water
- Discharged
- An ion is discharged when it gains or loses electrons and becomes an atom or molecule. Electrolysis of aqueous solutions
- Dm³
- A cubic decimetre, which is 1000 cm³ or one litre. Concentration and limiting reactants
- Dynamic equilibrium
- The state in which the forward and reverse reactions happen at the same rate, so amounts stay constant. Reversible reactions and equilibrium
- Effluent
- The liquid left after solids settle out of sewage. Earth's resources, potable water and waste water
- Electrolysis
- Breaking down an ionic compound, molten or in solution, using an electric current. Electrolysis
- Electrolyte
- The molten or dissolved ionic compound that conducts electricity. Electrolysis
- Empirical formula
- The simplest whole number ratio of atoms of each element in a compound. Empirical formulae and percentage composition
- End-point
- The point where the indicator changes colour and the reaction is just complete. Titrations and their calculations
- Excess
- More of a reactant than is needed. Some is left over at the end. Concentration and limiting reactants
- Fertiliser
- A substance added to soil to supply nutrients such as nitrogen to crops. The Haber process and fertilisers
- Finite resource
- A resource that will run out because it cannot be replaced as fast as we use it. Earth's resources, potable water and waste water
- Formulation
- A mixture designed as a useful product, made by mixing components in carefully measured quantities. Purity, formulations and chromatography
- Fossil fuel
- A fuel such as coal, crude oil or natural gas, formed from the remains of living things over millions of years. The Earth's atmosphere, past and present
- Galvanising
- Coating iron or steel with zinc. Corrosion, alloys and materials
- Gradient
- The change in y divided by the change in x for a line on a graph. Maths skills for chemistry
- Greenhouse gas
- A gas that absorbs infrared radiation from the Earth and releases it again, such as carbon dioxide, methane and water vapour. Greenhouse gases, climate change and air pollution
- Haber process
- The industrial process that makes ammonia from nitrogen and hydrogen. The Haber process and fertilisers
- Half equation
- An equation that shows what happens at one electrode, with electrons included. Electrolysis
- Halide
- A negative ion of a halogen, such as chloride, bromide or iodide. Electrolysis of aqueous solutions
- Hazard
- Something that could cause harm. Required practicals and working scientifically in chemistry
- Incomplete combustion
- Burning with too little oxygen, which makes carbon monoxide or carbon (soot). Greenhouse gases, climate change and air pollution
- Independent variable
- The variable you change in an investigation. Required practicals and working scientifically in chemistry
- Indicator
- A dye that changes colour to show when the reaction is complete. Titrations and their calculations
- Inert electrode
- An electrode, such as graphite, that does not take part in the reaction. Electrolysis of aqueous solutions
- Le Chatelier's principle
- If a change is made to a system at equilibrium, the system shifts to oppose the change. Reversible reactions and equilibrium
- Life cycle assessment
- A way of assessing the environmental impact of a product at each stage of its life: raw materials, manufacture, use and disposal. Life cycle assessments, recycling and getting metals sustainably
- Limewater
- A clear solution of calcium hydroxide that turns milky with carbon dioxide. Tests for gases
- Limiting reactant
- The reactant that is used up first and so decides how much product forms. Concentration and limiting reactants
- Mixture
- Two or more substances that are not chemically joined. Purity, formulations and chromatography
- Mobile phase
- The solvent that moves through the stationary phase. Purity, formulations and chromatography
- Mol/dm³
- The unit for concentration when it is given as moles of solute in each dm³ of solution. Concentration and limiting reactants
- Molar mass
- The mass of one mole of a substance, in grams per mole. The mole and reacting masses
- Mole
- The unit for amount of substance. One mole has 6.02 × 10²³ particles. The mole and reacting masses
- Molecular formula
- The actual number of atoms of each element in one molecule. Empirical formulae and percentage composition
- Ore
- A rock that contains enough of a metal compound to make it worth extracting the metal. Extracting metals by electrolysis
- Oxidation
- Loss of electrons. It happens at the anode. Electrolysis
- Particulates
- Tiny solid particles, such as soot, released into the air when fuels burn. Greenhouse gases, climate change and air pollution
- Peer review
- Checking by other scientists before results are accepted. Greenhouse gases, climate change and air pollution
- Percentage
- A fraction out of 100. Maths skills for chemistry
- Percentage by mass
- The part of the total mass of a compound that is a particular element, as a percentage. Empirical formulae and percentage composition
- Percentage yield
- Actual yield divided by theoretical yield, multiplied by 100. Percentage yield and atom economy
- Photosynthesis
- The reaction in which plants and algae use light to turn carbon dioxide and water into glucose and oxygen. The Earth's atmosphere, past and present
- Phytomining
- Using plants to take up metal compounds, then burning the plants to get ash containing the metal compounds. Life cycle assessments, recycling and getting metals sustainably
- Pipette
- A glass tube that measures one fixed volume of solution very accurately. Titrations and their calculations
- Position of equilibrium
- How far the reaction has gone: more products is to the right, more reactants is to the left. Reversible reactions and equilibrium
- Positive test
- The result you see or hear that shows a particular gas is present. Tests for gases
- Potable water
- Water that is safe to drink. Earth's resources, potable water and waste water
- Precise
- Repeat results that are close to each other. Required practicals and working scientifically in chemistry
- Pure substance
- A single element or compound, not mixed with any other substance. Purity, formulations and chromatography
- Reactivity series
- A list of metals in order of how easily they form compounds. Extracting metals by electrolysis
- Recycling
- Processing used materials so they can be made into new products. Life cycle assessments, recycling and getting metals sustainably
- Reduction
- Gain of electrons. It happens at the cathode. Electrolysis
- Relative formula mass (Mr)
- The sum of the relative atomic masses of all the atoms in the formula. Empirical formulae and percentage composition
- Renewable resource
- A resource that can be replaced as fast as it is used. Earth's resources, potable water and waste water
- Reuse
- Using a product again for the same job, such as washing and refilling a glass bottle. Life cycle assessments, recycling and getting metals sustainably
- Reversible reaction
- A reaction in which the products can react to make the reactants again. Reversible reactions and equilibrium
- Rf value
- Distance moved by a substance divided by distance moved by the solvent. Purity, formulations and chromatography
- Risk
- The chance that a hazard will cause harm, and how serious it would be. Required practicals and working scientifically in chemistry
- Rusting
- The corrosion of iron and steel to form hydrated iron(III) oxide. Corrosion, alloys and materials
- Sacrificial protection
- Protecting a metal by attaching a more reactive metal that corrodes instead. Corrosion, alloys and materials
- Sedimentary rock
- A rock formed from layers of material that settled and were squashed together. The Earth's atmosphere, past and present
- Side reaction
- An unwanted reaction that happens at the same time and makes other products. Percentage yield and atom economy
- Significant figures
- The digits in a number counted from the first non-zero digit. Maths skills for chemistry
- Simplest ratio
- The smallest whole-number ratio of moles of the substances in a formula or an equation. The mole and reacting masses
- Solute
- The substance that dissolves in a solvent to make a solution. Concentration and limiting reactants
- Standard form
- A number written as A × 10ⁿ, where A is between 1 and 10 and n is a whole number. Maths skills for chemistry
- Stationary phase
- The part of a chromatography set-up that does not move, such as the paper. Purity, formulations and chromatography
- Sustainable
- Using resources in a way that does not run them out or harm the environment. Percentage yield and atom economy
- Sustainable development
- Development that meets the needs of people today without stopping future generations meeting theirs. Earth's resources, potable water and waste water
- Tangent
- A straight line that touches a curve at one point and has the same slope as the curve there. Maths skills for chemistry
- Theoretical yield
- The maximum mass of product that could form, calculated from the equation. Percentage yield and atom economy
- Titration
- A method that finds the volume of one solution that exactly reacts with a fixed volume of another. Titrations and their calculations
- Titre
- The volume of solution added from the burette to reach the end-point. Titrations and their calculations
- Yield
- The mass of product you collect from a reaction. Percentage yield and atom economy
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