The Scientific Endeavour

Science is more than a collection of facts. It is a process: scientists observe something, ask a question about it, suggest an explanation, and test that explanation with experiments. If the evidence does not support the explanation, the explanation is changed.

Because of this, scientific knowledge can change when new evidence is found. People once believed that living things could appear on their own from non-living matter, such as maggots from rotting meat. Careful experiments showed that this does not happen.

1. 1Observe and ask

   Notice something and ask a question that can be tested: does the temperature of water affect how fast sugar dissolves?

2. 2Hypothesise

   Suggest a possible explanation or prediction, e.g. “sugar dissolves faster in hotter water”.

3. 3Plan a fair test

   Decide what to change, what to measure and what to keep the same. Choose apparatus and safety precautions.

4. 4Experiment and record

   Carry out the test, repeat it, and record the results in a table with units.

5. 5Analyse and conclude

   Look for a pattern — a graph helps — and decide whether the results support the hypothesis.

6. 6Communicate

   Share the method and results so that others can check them and repeat the experiment.

Good scientists also share a set of scientific attitudes — habits of mind that keep their work honest and useful.

Curiosity

Wanting to find out why and how things happen.

Creativity

Thinking of new ways to solve a problem or test an idea.

Integrity

Recording and reporting results honestly — even when they do not match your prediction.

Objectivity

Judging ideas by the evidence, not by personal feelings or by who suggested them.

Open-mindedness

Being willing to change your mind when there is new evidence.

Perseverance

Continuing to investigate when an experiment fails or gives unexpected results.

Science also affects society. Scientists have to consider whether an investigation is safe and ethical — for example, how animals are treated, or how a new technology might affect people and the environment.

A variable is any factor that can change in an experiment. To find out whether one factor affects another, you have to make the test fair.

• Change

  Independent variable

  The one variable you change on purpose. Example: the temperature of the water.

• Measure

  Dependent variable

  The variable you measure or observe to see the effect. Example: the time taken for the sugar to dissolve.

• Keep the same

  Controlled variables

  Everything else that could affect the result, kept constant. Example: volume of water, mass of sugar, amount of stirring.

Record results in a table with the unit in each column heading, e.g. “Temperature / °C” and “Time / s”. On a graph, plot the independent variable on the x-axis and the dependent variable on the y-axis.

• Repeat each measurement — usually three times — and calculate the average.
• Look out for an anomalous result: one that does not fit the pattern. Repeat that measurement and leave the odd value out of the average.
• Where you can, set up a control to compare against — for example, a plant given no fertiliser.

• Enter the lab only when a teacher is present, and follow instructions exactly.
• Wear safety goggles when heating or handling chemicals. Tie back long hair and tuck in loose clothing.
• Never eat, drink or taste anything in the lab. To smell a gas, waft it gently towards your nose with your hand.
• Report spills, breakages and injuries to your teacher immediately — however small.
• Know where the fire extinguisher, fire blanket, eye-wash station and first-aid kit are.
• Dispose of chemicals as instructed. Never pour them down the sink unless you are told to.

Containers of dangerous chemicals carry hazard symbols. Each symbol tells you the kind of danger, so you know which precautions to take.

• Flammable

  Catches fire easily. Keep away from flames, sparks and heat.

  e.g. Ethanol

• Corrosive

  Destroys skin and eyes, and attacks metals. Wear goggles and gloves.

  e.g. Concentrated acids and alkalis

• Toxic

  Can cause serious harm or death if swallowed, breathed in or absorbed through the skin.

  e.g. Mercury

• Harmful / irritant

  May irritate the skin, eyes or lungs, or be harmful in larger amounts.

  e.g. Some cleaning agents

• Oxidising

  Gives off oxygen, making other materials burn more fiercely. Keep away from flammables.

  e.g. Concentrated hydrogen peroxide

• Explosive

  May explode if heated, knocked or exposed to a flame.

  e.g. Fireworks

• Health hazard

  Can cause serious long-term harm, such as damage to organs or breathing.

  e.g. Some solvents

• Hazardous to the environment

  Harmful to water life. Never pour it down the sink.

  e.g. Copper(II) sulfate

Precautions must match the hazard. “Be careful” scores nothing. Name the action: keep a flammable liquid away from the Bunsen flame; wear goggles and gloves with a corrosive; use a toxic substance only as your teacher directs, in a well-ventilated area.

The drawings below are section diagrams — the way to draw apparatus in an exam: simple 2-D outlines in pencil, straight lines ruled, a label line to each part, and no shading.

Gas enters at the base and comes out of a small jet inside the barrel. Turning the collar opens or closes the air hole, which controls how much air mixes with the gas before it burns.

1. 1Place the burner on a heat-proof mat, away from the edge of the bench and from anything flammable.
2. 2Close the air hole.
3. 3Light the match or lighter first and hold it beside the top of the barrel, then turn on the gas tap.
4. 4Open the air hole gradually to get a blue, non-luminous flame for heating.
5. 5When you stop heating, close the air hole so the yellow safety flame is easy to see — or turn off the gas.

The hottest part of the non-luminous flame is just above the tip of the inner blue cone.

Scientists around the world use the same system of units — the SI units (International System of Units) — so that their measurements can be compared.

Choose an instrument that suits the size of the quantity and how precise you need to be. A measuring cylinder only a little bigger than the volume you need gives a more precise reading than a large one, because its scale divisions are smaller.

• Work out the value of one small division before you read any scale.
• Stand a measuring cylinder on a flat bench. Water curves at its surface (the meniscus); read the bottom of the meniscus.
• Keep your eye level with the mark you are reading. Reading from above or below gives a wrong value — a parallax error.
• On an electronic balance, press tare (zero) with the empty container on the pan, so the reading shows only the mass of what you add.
• To find the volume of an irregular solid such as a stone, lower it into water in a measuring cylinder: volume of stone = final reading − initial reading.
• Very thin objects are hard to measure one at a time. Measure many together — such as 100 sheets of paper — and divide by the number.
• Your reaction time affects stopwatch readings. Time several swings or events together and divide, to reduce its effect.
• Always write the unit. A number without a unit is not a measurement: “25” could mean 25 cm³, 25 g or 25 s, and answers without units lose marks.