Key terms: Introduction to Chemistry

The exam rewards precise definitions and correct terminology, so learn each term below exactly as written. The trickiest pairs to keep apart are observation versus inference and corrosive versus toxic, these are defined side by side so you can see the difference. Terms are grouped by content standard.

1.1 The scientific method

• Scientific method, The ordered process used to investigate a problem: observation, question, hypothesis, experiment, collection and analysis of data, and conclusion. It makes results reliable and repeatable.
• Hypothesis, A testable statement predicting the relationship between two variables, for example “the higher the temperature, the faster the reaction”. It is written before the experiment and later accepted or rejected.
• Observation, Information gathered directly with the senses or an instrument, such as “a colourless gas is produced”. It states only what is seen, not what it means.
• Inference, A reasonable conclusion drawn from an observation, such as “the gas is carbon dioxide”. An inference interprets the observation; it goes one step beyond it.
• Manipulated variable, The variable deliberately changed by the experimenter, such as the concentration of acid. It is the suspected cause being tested.
• Responding variable, The variable that is measured because it changes in response, such as the time taken to react. It must be a quantity that can be measured.
• Controlled (fixed) variable, A variable kept constant so the test is fair, such as temperature, volume or mass. Keeping it constant ensures the responding variable changes only because of the manipulated variable.
• Fair test, An experiment in which only the manipulated variable is changed while all other variables are controlled, so the conclusion about cause and effect is valid.
• Data, The measurements and observations recorded during an experiment, usually in a table with units in the headings. Data are analysed to find a pattern.
• Conclusion, A statement of what the results show, expressed as the relationship between the variables and whether the hypothesis is accepted or rejected.
• Aim, The purpose of the experiment, stating what is being investigated, for example “to investigate how temperature affects reaction rate”. It is not the same as a hypothesis, which predicts a relationship.
• Variable, Any quantity in an experiment that can change. Every described experiment has one manipulated, one responding and several controlled variables.

1.2 Laboratory apparatus and materials

• Laboratory apparatus, The instruments and equipment used to carry out experiments safely and accurately, each with a specific use and a correct name.
• Beaker, A wide cylindrical container for holding, mixing or heating liquids. It gives only an approximate volume and is not used for accurate measurement.
• Conical flask, A flask with a narrow neck and wide base for holding and swirling a solution, especially in titration; its shape reduces splashing.
• Measuring cylinder, A graduated tube for measuring an approximate volume of liquid. It is quick but less precise than a pipette or burette.
• Pipette, A tube that delivers one fixed, accurate volume, such as 25.0 cm³, used where an exact known volume is needed.
• Burette, A long graduated tube with a tap that delivers a variable, readable volume, used in titration to add liquid gradually and measure the volume used.
• Thermometer, An instrument that measures temperature in degrees Celsius (°C), read with the eye level with the liquid to avoid error.
• Bunsen burner, A gas burner giving a controllable flame; the blue flame is hot for strong heating, the yellow flame is cooler and luminous.
• Balance, An instrument that measures mass in grams (g); an electronic balance shows mass to a fixed number of decimal places.
• Meniscus, The curved upper surface of a liquid in a narrow tube; the volume is read from the bottom of the meniscus at eye level.
• Test tube, A small tube used to hold and heat small amounts of substance for a reaction; when heating, its mouth is pointed away from people.

1.3 Handling chemicals and laboratory safety

• Hazard symbol, A standard sign on a container warning of a specific danger, such as corrosive, toxic or flammable, telling you how to handle the chemical safely.
• Corrosive, Describes a chemical that attacks and damages skin, eyes or materials on contact, such as a concentrated acid or alkali; goggles and careful handling are needed.
• Toxic, Describes a chemical that is poisonous if taken in, swallowed, inhaled or absorbed; it is handled with care, often in a fume cupboard.
• Flammable, Describes a substance that catches fire easily; it must be kept away from flames and heat.
• Fume cupboard, An enclosed, ventilated workspace that draws away harmful gases and vapours, used when handling toxic or strong-smelling chemicals.
• Wafting, The safe way to smell a chemical, fanning a small amount of vapour towards the nose with the hand so concentrated fumes are not inhaled.
• Safety goggles, Protective eyewear that shields the eyes from splashes and flying particles; essential when handling corrosive substances.

1.4 Chemistry in daily life and careers

• Chemistry in daily life, The everyday uses of chemistry in food, medicine, materials, agriculture and energy; recognising them shows why the subject matters.
• Pharmacist, A chemistry-related career: a person who prepares and dispenses medicines and advises patients on their safe use.
• Chemical engineer, A chemistry-related career: a person who designs and operates the industrial processes that manufacture chemical products safely and efficiently.

How to use this glossary

Test yourself by covering the definitions and writing them from the term alone, then checking word for word. Pay special attention to the paired distinctions, observation and inference, corrosive and toxic, manipulated and responding, because muddling either pair is the most common way marks are lost in this chapter. A one-to-one teacher can quiz you on these definitions and check that your wording is precise enough to score, so the terminology is secure before it appears in the SPM Chemistry papers. Once the terms are automatic, move on to the practice questions and use this glossary to check every answer.