Freezing water

Freezing 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 planning an investigation.

Question 1Change answer

Raedon and Jen were talking about what happens to water when it freezes.
Raedon said, "When water changes to ice, it takes up less space."
Jen said, "When water changes to ice, it takes up more space."

a)  Write down the steps for a test to see who is right. The first step is done for you.
     1. Pour some water into a container and mark where it comes up to.

Question 1Change answer

b)  What results would you get from your investigation if Jen was right?
Task administration: 
This task can be completed with pencil and paper or online.
Levels:
3, 4
Curriculum info: 
Science, Investigating in science, Material World
Keywords: 
changes, freezing, water, ice, peer assessment, planning investigations
Description of task: 
Plan an investigation to find out which of two students' predictions is correct, and identify how to recognise what a result would look like. Assessment focus: identifying what to measure or compare to answer a science question.
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 that, when planning an investigation, the question we ask helps us to work out what to measure.
Science capabilities: 
Gather and interpret data
Answers/responses: 
  Y6 (06/2009) Y8 (06/2009)
a) The response must refer to both freezing the water, and measuring/comparing the ice with the water. difficult easy
 

The ice will be above the water mark.
Or
The container bulges/cracks/breaks.
(Do not accept "takes up more space").

 difficult moderate
Based on representative samples of 169 Year 6 and 171 Year 8 students.  
 
Teaching and learning: 

Nature of science idea
In science we carry out investigations to find
evidence to answer our questions.

Science concept
Water has unique properties that affect how it
behaves when it is heated or cooled.

Why is learning to plan an investigation important?
Science knowledge is built on observable evidence – this is one thing that makes science different from other disciplines. In “doing” science, students experience finding answers to their own questions. This helps them to understand what questions science can answer, and what it doesn’t.

In this task the emphasis is planning how to judge the result.

Why is learning about properties of water important?
Water is an element essential for life on our planet. To make decisions about environmental issues such as clean water supplies, water use, and global warming, we need to understand the properties of water, and how it behaves in different circumstances.
Diagnostic and formative information: 
Question a)
In the trial, Year 8 students were much more likely to describe a complete plan than Year 6 students.
This may be because:

•  They have had more experiences with planning an investigation;
•  They are more familiar with this particular investigation; or
•  They are better able to deal cognitively with a sequence of steps.
 

Incomplete responses - no way of comparing is provided.

Satisfactory responses

Put it in the freezer for a night or two (Y6)
Make sure it is a plastic container, put it in the freezer for a while then take it out. (Y6)
Then put it in the fridge or freezer and leave it overnight. Then get it out in the morning and it will be frozen. (Y8)

Then put it in the freezer for a night then take it out and mark where the ice is. Is it higher? (Y6)
Then place the container in the freezer so it can freeze. Give it a few hours. Then take it out and mark where it comes up to now. (Y8)

 

Question b)
Although Year 8 students did better than Year 6 students, a large number of students in both years did not state that the ice would be above the water mark if Jill was right. Some typical responses are listed in the table below.

Incomplete or incorrect responses

Misconceptions about the process of freezing
Does not describe what to do to check if the prediction was right, e.g.,

  You would have to check if she has been right. (Y6)
 
Attempts to explain why water behaves as it does but does not describe what to look for, e.g.,

  If you pour water into a container it will come up to a certain point, but because ice is   a solid not a liquid when the water freezes all the little particles will stop moving and move together, (Y8)
This student is using a developing understanding of particle theory that doesn't clearly explain the process of evaporation.  There is a possible misconception that ice takes up less space than liquid water.
Attempts to explain that Jill is wrong, rather than describe the evidence that her prediction is correct.

  The ice will take up a small space because water is heavier than ice. (Y8)

The density formula is the wrong way round – the denser ("heavier") material, i.e. water, will take up less space.

Examples of satisfactory responses where students clearly described what they would see included:

  • That when she marked the water it was lower than the ice so the ice takes up more space. (Y6)
  • The ice would be over the water mark line. (Y6) 
  • If I had 300ml of water when I froze it, it would be bigger and go up to 400-500ml. The water would expand while it was freezing. (Y8)
  • The frozen water would be a little bigger than the water itself. (Y8)
Next steps: 
Developing planning skills
Peer assessment: by following literally what is written in each others' plans students can critique each other's instructions.
They can then adjust their plans to reflect the feedback given.
  • Discuss that planning an investigation involves:

    • Being precise about what you will do;
    • How you will measure the result.
  • For resources to assist students to explore explanations, refer to an English resource, Changes of state (WL2655).
Other resources
  • Any activity that involves planning an investigation can be used to assess whether students can show how they will judge the results. 
  • The Making Better Sense books each include a section called What is an Investigation in Science?Templates are provided to help students with their plan, including what they will measure. (The templates do focus on fair testing.)
The following resources include developing concepts about ice:
For ARB resources, click on the link or search using the fields Material World, Levels 3 and 4, with keyword freezing.
  • Ministry of Education (2004). Ice, Building Science Concepts Book 58. Wellington: Learning Media. This book is aimed at Levels 1 and 2, and does not address the idea of ice taking up more space than liquid water, but does explore other aspects freezing.
  • Ministry of Education (1998). Making Better Sense of the Material World. A chapter on Water includes some activities about freezing water.