OCR · J248 · Gateway Science

OCR GCSE Chemistry A key terms

Absorption
The taking in of radiation by matter, transferring energy to that matter.
From: The Greenhouse Effect
Accuracy
A result close to the accepted or true value.
From: Measuring Rates of Reaction Practical

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Acid

A substance that forms hydrogen ions when it dissolves in water.

From: Neutralisation Reactions

Acid–base indicator

A dye that changes colour over a particular pH range and is used to show when the titration has reached its end point.

From: Titration of Strong Acids and Alkalis

Acidic

Having a pH below 7.

From: pH Scale

Acid rain

Rain made more acidic when atmospheric gases such as sulfur dioxide and oxides of nitrogen form acids in rainwater.

From: Atmospheric Pollutants

Activation energy

The minimum energy needed in a collision for reactant particles to react.

From: Collision Theory

Actual yield

The amount of product actually obtained and measured after carrying out a reaction.

From: Yield and Economy Calculations

Addition polymerisation

A reaction in which alkene monomers join as their carbon–carbon double bonds open, producing only a polymer.

From: Deducing Polymer Structures

Addition reaction

A reaction in which atoms join a molecule across a carbon–carbon double bond, producing one larger molecule.

From: Predicting Organic Reactions

Alcohol

A family of organic compounds containing a hydroxyl (–OH) group.

From: Functional Groups and Series

Alkali

A base that dissolves in water.

From: Neutralisation Reactions

Alkali metal

A Group 1 metal, such as lithium, sodium or potassium.

From: Group Properties

Alkaline

Having a pH above 7.

From: pH Scale

Alkane

A family of saturated hydrocarbons with carbon–carbon single bonds only.

From: Functional Groups and Series

Alkene

An organic compound containing a carbon–carbon double bond.

From: Deducing Polymer Structures

Allotrope

One of two or more structural forms of the same element in the same physical state.

From: Structural Representations

Allotropes

Different structural forms of the same element, produced when its atoms are bonded or arranged differently.

From: Giant Covalent Structures

Alloy

A mixture of two or more elements in which at least one element is a metal.

From: Alloy Composition and Uses

Alpha particle

A positively charged particle used to investigate atomic structure in the Geiger–Marsden scattering experiment.

From: Evolution of the Atomic Model

Amount

A quantity such as gas volume or mass that indicates how much reactant has been used or product has formed.

From: Rate Calculation Arithmetic

Amount of substance

The amount of substance, measured in moles (mol).

From: Concentration Relationships

Anhydrous substance

A substance from which the water in its crystal structure has been removed.

From: Reversible Reactions

Anion

A negatively charged ion.

From: Qualitative Analysis and pH Measurement

Anode

The positive electrode in an electrolytic cell, where negative ions lose electrons.

From: Electrolysis: Setup and Aqueous Solutions

Anomalous result

A plotted value that does not fit the pattern shown by most of the other values.

From: Data Interpretation

Anthropogenic

Anthropogenic means caused by human activity.

From: Anthropogenic Climate Change

Aqueous

A substance dissolved in water; the state symbol is (aq).

From: Ion Identification

Aqueous solution

A solution in which water is the solvent.

From: Solution Concentration

Aqueous solvent

A solvent in which water is the solvent or main solvent.

From: Chromatography Techniques

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