Boiling water

Boiling water

Pencil and paperOnline interactive
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about fair testing.
two-beakers-with-bunsen-burners.png
Jill and Toby wanted to see who could boil water the quickest.
The diagram above shows how they each set up their equipment.

Question

a)  i)  Whose water will boil faster? (Select one) 

    • Jill's

    • Toby's

ii) Why did you choose this answer?

Question 2Change answer

b)  Toby said a blue flame is hotter than a yellow flame. Jill was not so sure.
     To decide if Toby's statement is correct they set up a new experiment.
     Jill used a yellow flame and Toby a blue flame.
     What would they need to keep the same to be sure it was the colour of the flame they were testing?
Task administration: 
This task can be completed with pencil and paper or online.
Level:
5
Curriculum info: 
Science, Investigating in science, Material World
Keywords: 
changes, boiling, fair testing, variables
Description of task: 
Students decide on the variables that will make an experiment about boiling water a fair test. Assessment focus: Recognising multiple variables.
Curriculum Links: 
Science capabilities
The capabilities focus is brought about by the conversations you have and the questions you ask.
Capability: Gather and interpret data
This resource provides opportunities to discuss the importance of controlling variables when using fair testing for an investigation.

 

Science capability: Gather and interpret data (TKI)
 
Science capabilities: 
Gather and interpret data
Answers/responses: 
  Y10 (08/2009)
a)

i)
ii)

 Toby’s
In Toby’s experiment

• there was less water to heat
• the beaker of water is closer to the flame so the water will heat up more quickly
• the beakers are different sizes with different sized bases which affects how much of the water is exposed to the heat from the flame

(or the opposite of the above if they discuss Jill’s experiment)

very easy

All 3 identified - very difficult
2 identified - difficult
1 identified - very easy
b)

 
• Same amount of water
• Same size tripod or distance of the beaker to the flame
• Same size/shape beaker
• Same initial temperature of water
• Same amount of time for heating water/ begin both experiments at the same time
• Same environmental conditions e.g. experiments conducted at the same room temperature, exposure to drafts/the sun and light conditions in the room are the same etc.

All identified - very difficult
3 identified - difficult
1-2 identified - very easy
Based on a representative sample of 252 Year 10 students 
Teaching and learning: 
This resource uses a simple context and is a good diagnostic activity to show how many relevant variables students identify without prompting.
Diagnostic and formative information: 
  Common response Likely misconception
a) ii)

Most students gave only one variable.

Some students identified the amount of water and the size of the beakers.

Most students answered that Toby had less water than Jill. However, a few of the students also explained that less water would take less time to boil. Many students ignored the second important variable, the distance of the water from the flame.

Although the size of the beakers is a variable in this experiment it has little impact in comparison to the variables of distance to the flame and amount of water to heat.

See Next steps.
b)

Most students again gave just one variable.

Very few students mentioned the variable of time.

Some students said the amount of gas being let through the Bunsen burner.

The most common variable given was the same amount of water.

When it was included it was not explained. For example most students who included time just said “same time” rather than heat for the same amount of time or begin experiments at the same time.

These students are not clear about what they understand about the mixture of the gas and that it is the amount of oxygen in the fuel which affects the heat of the flame. This amount of oxygen is the independent variable, and it does need to be different so that a comparison can be made in the data.

 

Next steps: 
Identifying multiple relevant variables
Students easily identified one variable which did affect the experiment. However few listed multiple variables. Students need to look at each investigation as one whole system and consider all the variables that could impact on this system. They could practise this by considering the variables in other simple familiar investigations. For example, if using the “burning peanut”, you could direct students to consider the range of relevant variables and explain why each one needs to be considered. For example:

  • the size of the peanut  - do larger peanuts have more oil?
  • the age of the peanut - do older peanuts have less oil?
  • the amount of heat used to initiate the burning – will quickly catching the peanut alight waste less oil?
  • the experimental techniques, e.g., height of the boiling tube above the flame, timing issues, measuring issues, etc.

Understanding the impact of a variable
Once students have thought about the range of variables they could then decide how much of an impact each variable would make. For example in the boiling water experiment some students identified that the beakers were of different sizes. However this variable may have little effect on the outcome because although a larger surface area on the base of a large beaker allows water in the beaker to heat up more quickly than the water in a smaller beaker (heat from the flame is in contact with more water) in this experiment, it is the amount of water that mainly affects the outcome. The larger beaker holds about twice as much water as the smaller beaker so the relative advantage of greater surface area for its base is more than cancelled out. Students could plan and carry out experiments to investigate this, in doing so gaining more practise at managing the other variables.
 

  • There are many ARB resources that focus on fair testing and control of variables.
  • Use the key words “fair testing” and “variables” plus the context you are focussing on to find other resources.
  • Science investigations gives a brief summary of different sorts of investigations.