Burning candle diagram

Burning candle diagram

Pencil and paperOnline interactive
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about showing the changes that happen when a candle burns.
candle burning
When a candle is burning, some of the wax melts, and some of it is used as fuel.
If you were able to see the molecules of wax as the candle burns, what do you think you would see happening?

Question Change answer

Draw a picture of a burning candle to show all the ways that the wax changes.
Add labels to help other people understand your picture.
Task administration: 
This task can be completed with pencil and paper or online.
Level:
5
Curriculum info: 
Science, Communicating in science, Material World
Key Competencies: 
Using language, symbols, and texts
Keywords: 
changes, nature of matter, burning, particles, diagrams, drawing, key competencies
Description of task: 
Task: Students draw a picture of a burning candle to show changes that occur. Assessment focus: representing the way particles behave when material undergoes temporary and permanent changes.
Answers/responses: 
  Y10 (09/2007)
Drawings included representation of particles very difficult
 
Based on a representative sample of 294 Y10 students.

NOTE: Level 4 in the new curriculum states that students will "begin to develop an understanding of the particle nature of matter and use this to explain observed changes".

Asking students to represent particles by drawing gives teachers opportunities to assess both students' knowledge about the particle nature of matter and their ability to communicate science ideas (Nature of science strand).

Diagnostic and formative information: 

In this task, students were specifically asked to think about what they would see happening when a candle burns if they were able to see the molecules of wax. Most students indicated that they knew something about the changes that occur when a candle burns but did not attempt to show changes happening at this "micro-level". Instead, they drew the changes you would directly observe if you were watching a candle burn.

Only 41 students out of the sample of 294 students represented molecules in their drawings. Of those that did, twenty six students showed they knew something about how the behaviour of molecules changed when material changed state (although only six of these students' drawings included representations of gas). Only one of these students represented combustion.

Many students in the trial identified this task as difficult and almost 10% of the students made no attempt to answer this question. Several students commented that they found it difficult to express their ideas in drawings, although others said they welcomed alternative ways of showing what they knew.

What is this assessment really telling us?
Talk to the students to check whether or not they understood what the task was asking of them.

  • What exactly does the task ask you to do?
  • Where in the question does it ask you to think about what is happening to the molecules of wax?
  • Why does it say you should add labels?

This is an opportunity to support students to develop effective strategies to ensure they are actually answering the question that is being asked. If the students did understand the task but still did not represent changes at a "micro-level" was it because they did not understand these changes or because they did not know how to represent them?

What do the students' drawings tell us about their science content knowledge?

The focus of this task was on how students represented the changes at a "micro-level" when a candle burns. Approximately 70% of students in the trial did not represent changes at this level, or in fact represent molecules at all in their drawings. However, many of these students still demonstrated that they knew that wax was changing from a solid to a liquid (and back again), and some knew that the wax changed from a liquid to a gas. A few also knew that the wax in its gas form was burning. Other students showed misconceptions in their understanding about the processes involved. So, although the focus in this task is the nature of science, the task clearly shows that the content itself is still important.

Next steps: 

The task provides opportunities to develop ideas about the conventions that are used in science when representing ideas visually. A range of students' pictures could be discussed and questions asked:

  • What do the pictures show and what don't they show?
  • Are there lines or arrows in the pictures? What do they represent? How do we know?
  • Are there labels? Do the labels make the ideas clearer? If so, how?
In this task students are also being asked to represent things (molecules) that are too small to see. This is an opportunity to talk about the use of models in science as a tool to understand phenomena that are too small for us to see. In discussing models it is important to talk about how the model is similar and how it is different from the "real" thing. You could talk too about a variety of ways "micro-level" changes could be represented in diagrams e.g., enlarged insets in the diagrams and the use of labelling or keys. Students could be challenged to look through books (or go on line) and find alternative ways of representing things that are too small to see. They could also come up with their own representations and compare and critique these.

Exemplars

  • This Level 5 exemplar shows a student's progress in using representations to describe the nature of matter: It's elementary

On the Science Is site there are two activities that explore scientists' representations of atoms:

  • Level 5-8, Models of the atom from Democritus to Rutherford
  • Level 5, Selecting models of atoms

Ministry of Education (2004). Building Science Concepts, Book 64, Candles: Investigating combustion. Wellington: Learning Media.