Science: Working Scientifically and Practical Skills Set 3
Working scientifically and practical skills, set 3, extends the working-scientifically strand with graph skills: choosing the right chart type, drawing a line of best fit, reading values by interpolation or extrapolation, finding a rate from a gradient, and using hazard symbols safely.
Before you start
Make sure you're comfortable with these topics first:
Method
- Before drawing a graph, decide whether the independent variable is categoric (grouped into distinct categories, such as different metals) or continuous (able to take any numerical value, such as time or temperature), since this determines whether a bar chart or a line graph is the appropriate choice.
- When drawing axes for a line graph, choose a scale that uses as much of the graph paper as sensibly possible and that is easy to read, for example rising in 2s, 5s or 10s, then label each axis with both the variable and its unit.
- Plot each data point accurately as a small, clear cross or dot, then draw a single smooth line of best fit that shows the overall trend, rather than joining the points dot-to-dot.
- Use the line of best fit, not the raw data points, to read off any value asked for between two measured points (interpolation), and be more cautious about a value read from well beyond the measured range (extrapolation), since the pattern may not continue.
- To find the rate of a reaction or process from a graph, calculate the gradient, the change in the y-value divided by the change in the x-value, over the steepest, most consistent part of the line.
- Before starting any practical, check the hazard symbols and safety instructions given for each chemical or piece of equipment, and identify at least one sensible precaution linked to each hazard identified.
- When a preliminary (trial) run gives a very fast or very slow result, adjust the range or number of values planned for the main investigation accordingly, rather than repeating the same range and hoping for a clearer pattern.
Worked example
A student collects the volume of gas produced during a reaction between marble chips and hydrochloric acid, plotting a graph of volume of gas (cm^3) against time (s). Her line of best fit passes through (10 s, 20 cm^3) and (30 s, 60 cm^3) over its steepest, most linear section. Use gradient = change in y / change in x to calculate the rate of reaction over this section, in cm^3/s.
- Find the change in the y-value (volume of gas): 60 - 20 = 40 cm^3.
- Find the change in the x-value (time) over the same section: 30 - 10 = 20 s.
- Divide the change in y by the change in x: 40 / 20.
- Final answer: rate of reaction = 2 cm^3/s.
Practice questions
Type your answer and press Check to be marked straight away, or reveal the answer and mark yourself.
Q1A student investigates how the mass of five different metal samples affects their volume, with mass as a continuous numerical variable. State whether a bar chart or a line graph is the more appropriate way to display these results.Show answer
Answer: A line graph, because mass is a continuous variable.
Q2State the name given to a value read from a graph that lies between two points that were actually measured.Show answer
Answer: An interpolated value (interpolation).
Q3State the name given to a value read from a graph beyond the range of the data that was actually measured.Show answer
Answer: An extrapolated value (extrapolation).
Q4A hazard symbol shows a skull and crossbones on an orange background. State what hazard this represents.Show answer
Answer: Toxic (poisonous).
Q5On a graph of temperature (y-axis) against time (x-axis), a straight line rises from (0 s, 20 degrees C) to (40 s, 60 degrees C). Calculate the gradient of this line, and state what it represents.Show answer
Answer: 1 degree C per second ((60 - 20) / (40 - 0) = 1); it represents the rate at which the temperature increases.
Q6State why it is good practice to run a quick preliminary (trial) experiment before starting the main investigation.Show answer
Answer: To check that the chosen range and number of values give measurable, sensible results, and that the method and timing work, before committing to the full investigation.
Q7A student wears safety goggles when heating a test tube of liquid over a Bunsen burner. State the hazard that the goggles help protect against.Show answer
Answer: Hot or splashing liquid, or steam, reaching and injuring the eyes.
Exam-style questions
Written in the style of a 13+ Common Entrance exam paper, with a full mark scheme.
A student times how far a trolley travels from rest down a ramp at 1 second intervals, then plots a graph of distance travelled (y-axis, in cm) against time (x-axis, in seconds). The line of best fit is straight and passes through the points (2 s, 30 cm) and (6 s, 90 cm). (a) Calculate the gradient of the line of best fit between these two points, showing your working. (b) State what this gradient represents, including its unit. (c) The student wants to know the distance travelled at 4 s. State whether reading this value from the graph would be an example of interpolation or extrapolation, and explain your answer.
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A technician sets up an experiment for a class using a chemical labelled with a hazard symbol showing a flame over a circle, and reminds pupils to keep the chemical away from all naked flames and heat sources. (a) Name the hazard that this symbol represents. (b) A pupil wants to investigate how the concentration of this chemical affects the rate of a reaction with a metal. State the independent variable and the dependent variable for this investigation. (c) Suggest one variable that should be kept the same for this to be a fair test.
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Free printable worksheet
Want more practice on paper? Download the science: working scientifically and practical skills set 3 worksheet pack - 19 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 17 of 13+ Science Workbook, the whole course as one free printable PDF.
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