Part 1 · Why the Laboratory Has Rules

A science laboratory is not an ordinary classroom. It contains gas taps, electrical sockets, glassware and bottles of chemicals, and you will heat things with an open flame. Every one of those things is useful, and every one of them can hurt you if it is used carelessly. That is why a laboratory has its own set of rules.

A laboratory also contains equipment that is there purely to keep you safe. A fire blanket and a sand bucket smother small fires. A fire extinguisher puts out larger ones. An eyewash bottle washes chemicals out of your eyes. A fume cupboard traps dangerous gases so you do not breathe them in. A glass bin takes broken glassware so that nobody is cut clearing it away.

Every laboratory has a set of rules that you must follow in every single lesson. They are not suggestions. Most accidents in school laboratories happen because somebody decided that one of the rules did not apply to them.

Laboratory safety rules

• Never enter the laboratory without permission.
• Always wear safety goggles when heating substances or using chemicals.
• Always tie back long hair and tuck your tie into your shirt when heating.
• Always stand up, with your stool pushed under the bench, during experiments.
• Always place bags and coats under the desk, out of the way.
• Never eat or drink in the laboratory.
• Never run in the laboratory.
• Always tell your teacher about spillages or breakages immediately.
• Never poke anything into the electrical sockets.
• Never turn on a gas tap without permission, and turn it off when finished.

Part 2 · Hazard, Risk and Control

Read the passage and study the diagram, then answer the questions.

Scientists do not simply call things 'dangerous'. They use three more precise words instead. A hazard is the thing that could cause harm. A risk is what could actually happen to you because of that hazard. A control is the thing you do to stop the risk from happening.

Take a Bunsen burner. The hazard is the open flame. The risk is that you burn your hand or set your hair alight. The controls are tying your hair back, wearing goggles and standing up so that you can move away quickly. Notice that one hazard can create several different risks, and each risk may need its own control.

Before any practical work you should look at the equipment and chemicals you have been given and identify the hazards. This is called a risk assessment, and professional scientists write one before every experiment they carry out.

Part 3 · Hazard Symbols

Study the hazard symbols, then answer the questions.

Some of the chemicals used in a laboratory are dangerous, so every bottle and container carries a hazard symbol. The symbols are printed on the side of the container. They tell you at a glance whether the chemical is dangerous and, just as importantly, in what way it is dangerous.

Hazard symbols are pictures rather than words, which means a scientist can understand them no matter what language they speak. Every symbol is drawn as a red diamond with a black picture inside it.

Part 1 · Drawing Scientific Diagrams

Read the passage and study the diagram, then answer the questions.

In science you draw a diagram of apparatus rather than a picture of it. A picture tries to show what the apparatus really looks like, with shading and 3D curves. A diagram shows what you would see if you cut the apparatus in half and looked at the cut edge. This is called a cross-section.

Diagrams are quicker to draw, easier to copy accurately, and much clearer when several pieces of apparatus are joined together. Because every scientist draws the same apparatus the same way, a scientist anywhere in the world can read your diagram even if they do not speak your language.

Rules for drawing apparatus

• Always use a pencil, never a pen.
• Always use a ruler for straight lines.
• Never shade, and never make the apparatus look 3D.
• Draw the cross-section — the view you would see if it were cut in half.
• Draw the same apparatus the same way every time.
• Label each piece of apparatus with its proper name.

Part 2 · Reading a Measuring Cylinder

Read the passage and study the diagram, then answer the questions.

When a liquid is put into a narrow container, its surface is not flat. It curves downwards in the middle, forming a shape called the meniscus. The reading is always taken from the bottom of the meniscus.

Your eye must be level with the bottom of the meniscus when you take the reading. If you look down from above, the reading comes out too high. If you look up from below, it comes out too low. This kind of error is caused by the position of the observer, not by the equipment.

Part 3 · Working Out the Scale

Read the passage and study the diagram, then answer the questions.

Every measuring instrument has a scale — a set of marked lines. Before you read any scale you must work out what one small division is worth. Two measuring cylinders can look almost identical and yet have completely different scales, so guessing is not good enough.

To find the value of one small division, take the gap between two numbered lines and divide it by the number of small divisions in that gap.

Reveal Answers

7 ml

12 ml

35 ml

60 ml

15 ml

150 ml

24 ml

350 ml

Part 4 · Planning to Measure the Mass of Water

Read the passage and study the diagram, then plan your risk assessment.

Next lesson we are going to measure the mass of specific volumes of water — for example the mass of 10 ml, 20 ml and 30 ml. Before any practical work, scientists write a risk assessment: they list what could cause harm, what could happen, and how they will keep everyone safe.

You will stand a measuring cylinder on a balance, add water to a measured volume, and record its mass. The diagram shows the equipment you will use.

Part 1 · Types of Variable

Read the passage and study the diagram, then answer the questions.

In science, anything that might affect the outcome of an investigation is called a variable. The thing that changes as a result is also a variable. There are three types, and every investigation has all three.

The independent variable is the one you deliberately CHANGE. The dependent variable is the one you MEASURE. The control variables are all the others, and you KEEP THEM THE SAME. Controlling them is what makes the test a fair test: if two things changed at once you would not know which one caused the result.

For example, in an investigation into how the temperature of water affects how much sugar dissolves, the independent variable is the temperature of the water, the dependent variable is the mass of sugar that dissolves, and the control variables include the volume of water and the apparatus used.

Part 2 · Drawing a Results Table

Study the rules, then complete the task below.

Rules for a good results table

• The independent variable goes in the first column.
• The dependent variable goes in the columns to the right of it.
• Every column has a clear heading.
• Every heading gives the unit, written in brackets.
• Units are written in the heading only, never next to each number.
• Repeat readings each get their own column, with a final column for the mean.

Part 3 · Measuring the Mass of Water

Read the method, then answer the questions.

In this practical you will measure the mass of different volumes of water.

The measuring cylinder itself has a mass, which would be included in every reading. To remove it we use taring: stand the empty cylinder on the balance and press the tare button so the display reads zero. The balance now shows only the mass of the water you add.

Class practical — mass of water

• Stand an empty measuring cylinder on the balance.
• Press tare so the balance reads 0.0 g.
• Add water until it reaches the 10 ml line, reading the bottom of the meniscus at eye level.
• Record the mass shown on the balance.
• Repeat twice more, taring each time.
• Repeat for 20 ml, 30 ml and so on, up to 100 ml.

Part 4 · Means and Anomalies

Study the results table, then answer the questions.

An anomaly (or anomalous result) is a reading that does not fit the pattern of the others — it is much too high or much too low. Anomalies are usually caused by a mistake in the measurement, so we circle them and leave them out when we calculate a mean.

Calculating the mean

Repeat readings are never identical, so we calculate a mean — the value we would expect if the measurement were perfect. To find the mean, add the readings together and divide by how many readings there were.

We don't include anomalies in our mean calculations.

Part 1 · Bar Chart or Line Graph?

Read the passage and study the diagrams, then answer the questions.

A table stores results, but a graph shows the pattern in them. Choosing the wrong type of graph hides that pattern, so the choice is made before you draw anything.

The rule is simple, and it depends on the independent variable. If the independent variable is described in words — colours, materials, types of food — draw a bar chart, with a gap between each bar. If both variables are numbers you have measured — time, length, temperature, volume — draw a line graph.

Whichever you draw, the independent variable always goes on the horizontal x-axis and the dependent variable always goes on the vertical y-axis.

Part 2 · Drawing a Graph

Read the passage, then plot your graph.

We will now plot a graph for our experiment last lesson, finding the mass of water. Which type of graph should we use?

Rules for plotting a graph

• Give the graph a title.
• Put the independent variable on the x-axis and the dependent variable on the y-axis.
• Label both axes with the name of the variable and its unit.
• Start each axis at zero and go up in regular steps (1, 2, 3… or 2, 4, 6…).
• Make the graph fill about three quarters of the paper.
• Plot each point with a small, neat X.
• Draw a single line of best fit — do not join the dots.
• Use a ruler for straight lines, and pencil throughout.

An axis that goes up in irregular steps is the most common mistake. If the x-axis jumps 0, 10, 20, 50, 100, the shape of the line is meaningless, because equal distances along the axis no longer mean equal changes.

Part 3 · Lines of Best Fit and Checking a Graph

Study the diagrams, then answer the questions.

A line of best fit passes as close to as many points as possible. It does not have to go through every point, and it must never be drawn dot to dot. Where the points curve, draw a single smooth curve instead of a straight line. Never sketch the line several times — a fuzzy, 'feathered' line cannot be read accurately.

Once a graph is finished, check it against the criteria before handing it in. Every one of the criteria below is worth a mark, and every one of them is easy to lose.

Line graph checklist

• Title
• x-axis is linear
• x-axis labelled with a unit
• y-axis is linear
• y-axis labelled with a unit
• Points plotted as a small X
• A single line of best fit
• Ruler used and drawn in pencil

Part 1 · The Parts of the Bunsen Burner

Read the passage and study the diagram, then answer the questions.

The Bunsen burner is the main heat source in a school laboratory. It burns methane gas, which is supplied through the gas tap on the bench. It is named after Robert Bunsen, who developed it in 1855.

Gas travels from the gas tap along the hose and into the base of the burner. It then rises up the chimney, which is the tall metal tube. Near the bottom of the chimney is the collar, a metal ring that can be turned. Turning the collar opens or closes the air hole, and this is the only control you have over the flame.

The flame itself has two parts. The outer cone is the pale region around the edge of the flame. The inner cone is the darker region in the middle, where the gas has not yet burned. The burner always stands on a heatproof mat so that the bench is not damaged.

Part 2 · Lighting the Bunsen Burner Safely

Read the method, then answer the questions.

There is one correct order for lighting a Bunsen burner, and it matters. The air hole must be closed before you light it, because a closed air hole gives a large, visible yellow flame. If the air hole is open when you light the burner, the flame is almost invisible and somebody can be burned without realising the burner is lit.

The splint must also be lit and held above the chimney before the gas is turned on. If you turn the gas on first, unburned gas builds up in the room while you look for a light.

If the burner goes out for any reason, turn the gas off at the tap immediately and tell your teacher before relighting it.

Part 3 · The Three Flames

Turning the collar changes how much air mixes with the gas, and that changes the flame completely. More air means more oxygen, which means the gas burns more completely and the flame gets hotter.

Class practical — lighting a Bunsen burner

• Clear bags and books from the bench and push your stool under.
• Put on safety goggles, tie long hair back and tuck your tie in.
• Check the hose for splits or holes. If you find any, do not use the burner — give it to your teacher.
• Stand the burner on a heatproof mat and connect the hose to the gas tap, but do not turn the tap on.
• Close the air hole by turning the collar.
• Light a splint and hold it about 2 cm above the top of the chimney.
• Your partner now turns on the gas tap. The burner lights with a yellow flame.
• Adjust the collar to make each flame, and record what you see in the table below.
• To turn the burner off, switch off the gas at the gas tap.

The safety flame is never used for heating. It burns the gas incompletely, which produces soot — a layer of black carbon that coats the bottom of any glassware held in it. The burner is left on the safety flame between heatings so that everyone can see it is still lit.

Part 4 · Heating Different Amounts of Water

Read the method, then carry out the experiment.

In this experiment you will find out how the amount of water affects how long it takes to heat it. You will heat different volumes of water until each reaches 40 °C, timing how long it takes, and then draw a graph of your results.

You will always heat the water on the fully open (roaring) flame, changing only the volume of water each time. The volume of water is the independent variable.

Class practical — heating water

• Measure 50 ml of cold water into a beaker and stand it on the gauze and tripod.
• Place the thermometer in the water and record the starting temperature.
• Light the Bunsen burner and set the air hole fully open.
• Start a timer, and stop it when the water reaches 40 °C. Record the time.
• Turn the burner to the safety flame while you set up the next volume of water.
• Repeat with 100 ml, 150 ml, 200 ml and 250 ml of water.