Teaching activity – Identifying the mystery substance
This resource for level 3–4 students supports the science capability "gather and interpret data".
About this resource
A mystery substance has been found. Your challenge is to learn what investigations can be used to identify substances and then to use this knowledge to solve the mystery of what the substance is.
Teaching activity: Identifying the mystery substance
Curriculum links
Level 3 and 4
Nature of Science: Understanding in science
Students will:
- appreciate that science is a way of explaining the world
- identify ways in which scientists work together and provide evidence to support their ideas.
Level 3 and 4
Nature of Science: Investigating in science
Students will:
- build on prior experiences, working together to share and examine their own and others’ knowledge
- ask questions, find evidence, and carry out appropriate investigations to develop simple explanations.
Level 3 and 4
Material World: Properties and changes of matter
Students will:
- group materials in different ways based on the observations and measurements of the characteristic chemical and physical properties of a range of different materials.
Mātauranga Māori
In this activity, students closely observe a range of substances and their responses to a range of diagnostic tests. The characteristic responses can be used to identify the substance.
Close observation is important to Māori, and mātauranga, pūrākau (narratives), ngā tohu o te taiao (environmental signs), and the close connection Māori informs the maramataka and knowledge about how to create the best conditions for growth.
For example, the oral traditions of Tainui tell of how Whakaotirangi was tasked with looking after the kūmara on the seafaring voyage to Aotearoa. Upon arrival, Whakaotirangi had to find a place where the kūmara could be cultivated and stored.
Whakaotirangi used her close observation skills and knowledge of the growing conditions needed for the kūmara to select where, in the colder climate of the new land, she thought the kūmara would be able to grow. This process involved observing the plants’ response to the growing conditions and carefully considering modifications to the environment to successfully grow healthy kūmara.
See Whakaotirangi and her Kete of Kūmara (Connected, Level 2, 2020) and supporting resources curated by the Science Learning Hub - Pokapū Akoranga Pūtaiao for more. At the end of the activity described below, students could discuss connections between what they have done and what Whakaotirangi needed to think about.
Learning activity 1: Identify characteristics of a range of substances
Students will:
- develop the science capability gather and interpret data to identify some characteristics of a range of substances (castor sugar, ground salt, white flour, baking soda, baking powder, and citric acid). This involves making close observations and recording them
- understand that the properties of a substance can be measured and used for classification purposes on the basis of the similarities and differences from the diagnostic tests.
- access to sinks and cleaning and drying cloths
- eight sets of a range of common (non-toxic) white powders (one teaspoon of each in separate small containers with the name of the substance on the container):
- Castor sugar
- Salt (ground)
- White flour
- Baking powder
- Baking soda
- Citric (or tartaric) acid.
- test tubes (or equivalents, for example, small glass jars) per group
- jar lids made from metal are suitable for heating
- metal tongs or forceps (not plastic)
- a candle
- matches
- white vinegar and water
- litmus paper (either neutral paper, or both red and blue paper)
- copies of diagnostic test instruction sheets for each team of consultants; See Materials that come with this resource to download Teaching activity: Identifying substances - Student copy (.doc) and Teaching activity: Identifying mystery substances – Teacher copy (.doc).
A note about safety
Care must always be taken with unknown substances with unknown properties. Students need to understand that any of these diagnostic tests could release toxic fumes or have violent reactions with some substances (although not the ones selected for this activity).
Scientists have built knowledge over time through research and study of ways to ensure safety. Students could investigate the history of some of the discoveries about the reactivity of substances and the incidents that occurred to alert them to the potential dangers. (Students may not recognise that even water can produce some extreme and dangerous reactions. (See, for example, Sodium and water reaction and Calcium carbide and water on YouTube.)
See Materials that come with this resource to download Safety and Science Putaiao School labs guidance (.pdf).
- Substances, objects, and materials have physical and chemical properties.
- A property is a feature of a substance, object, or material.
- The properties can be identified using our senses and scientific equipment to observe, measure, and test.
- How do you think someone could find out what type of substance something is (by using our five senses, measuring, testing, comparing, and contrasting)?
- What do you think scientists mean when they say most substances have distinctive properties?
- What are some of the properties we know about? (If not already covered, suggest ‘solubility’, ‘acidity’, ‘reaction with acids’, ‘melting temperature’. For clarification of terms, see Materials that come with this resource to download Teaching activity: Identifying substances - Teacher copy (.doc)).
- What questions do you think we could ask when trying to find out what an unknown powder is? (Record questions)
- What made you think of the questions?
- How can we decide which questions we might be able to investigate ourselves in the classroom?
- Are there any skills/techniques we need to develop before the investigation?
- Explain to the students that they are going to learn to carry out some tests that can be used to explore the properties of substances.
- Divide the class into eight teams of consultants:
- Two teams of solubility consultants
- Two teams of acid reaction consultants
- Two teams of melting consultants
- Two teams of acidity consultants.
- Each team will have a different diagnostic test to perform (there are four different tests and eight teams). Hand out one diagnostic test instruction sheet to each team and explain that they will become specialists at using that diagnostic test. Explain the need for avoiding contamination by cleaning thoroughly between substances.
- Issue a set of powders to each team and give students about 15–20 minutes to complete the diagnostic tests to answer the investigation question on their team’s diagnostic test instruction sheet, and record their observations for each substance.
- Have the teams working on the same test meet and compare their processes and results. Ask questions like:
- What did you do?
- Was your process the same as ours?
- Are our results the same or different?
- As a class, use the information from each team to fill in the table of substances and their distinctive properties. See Materials that come with this resource to download Teaching activity: Identifying mystery substances - Student copy (.doc).
- Did your team get the same results for your diagnostic tests as the other team using the same tests? If there were any differences in your results, what could explain these differences?
- How do the results of the test help you describe the properties of the mystery substances?
- What is the advantage of practising your diagnostic test before using it on a mystery substance?
- How important is a scientist’s experience when developing a research question?
Learning activity 2: Identify a mystery substance
- Use their prior knowledge to make a prediction as to the identity of the mystery substance.
- Gather and interpret the data, noting the results of the diagnostic tests.
- Record data from their tests using appropriate science recording practices, for example, using a table (interpret representations).
- Use evidence to support their conclusion as to what the mystery substance might be
- Reflect on why having multiple forms of evidence is important for forensic scientists (critique evidence).
- access to sinks and cleaning and drying cloths
- eight unlabelled containers of a substance – you could have two lots of different substances, and students could work in the same groups as previously to identify their substance
- test tubes or equivalents, for example, small glass jars for each group
- glass jar lids (metal), for example, jam or chutney lids suitable for heating
- tongs or forceps
- a candle
- matches
- white vinegar and water
- litmus paper, either neutral paper, or both red and blue paper
- the last page of Teaching activity: Identifying mystery substances - Student copy (.doc). See Materials that come with this resource to download.
Review the previous activity with the class. Recall the diagnostic tests you used. Show the class the mystery substance.
- What did you learn from your diagnostic tests that could help you predict what the substance might be?
- What are some diagnostic questions you could investigate in class to determine what the substance is? (Record questions)
- Divide the class into the same eight teams of consultants as in the first activity.
- Ask the students to imagine that they are a team of forensic scientists who have been asked to identify a mystery substance found at a crime scene.
- Issue a sample of the unknown substance to each of the eight teams and ask them to conduct their specialist tests on it.
- Students record their observations about the results of their diagnostic test on the mysterious substance.
- See Materials that come with this resource to download Teaching activity: Identifying mystery substances - Student copy (.doc).
- Full class report-back session. Have each team report the results of their test on the mystery substance and suggest what they now think the substance is, providing specialist, supporting evidence.
Alternatively
- Issue the same mystery sample to two groups.
- Ask students to perform the full raft of tests on their mystery substance to identify it.
- The two groups are then asked to share their results with each other.
- Did they get the same results? Did they come to the same conclusion as to the identity of the substance? Why or why not? This provides a great opportunity to critique their experimental technique, their data recording, and the inferences they draw from their data.
- What do you think the mystery substance is? What prior knowledge did you use to make that prediction?
- How useful were your questions in guiding your diagnostic testing?
- Was it helpful to have predictions about the results?
- How did your confidence in your prediction change as more teams reported their findings?
- How confident do you feel about your own team’s specialist test results? Do you think you would be as confident if you did one of the other tests without practising first?
- Was it more efficient when specialist teams shared their findings and arrived at a combined decision?
- How much confidence should a court or jury have in just one piece of evidence?
- Identify connections between this activity and what Whakaotirangi needed to think about when looking for a place to grow kūmara in the new land (see Whakaotirangi and her Kete of Kūmara (Connected, Level 2, 2020) and supporting resources curated by the Science Learning Hub - Pokapū Akoranga Pūtaiao)
- Use this activity as a starter for a unit on forensic science
Other resources
- Properties of materials: An introduction - Science Learning Hub - Pokapū Akoranga Pūtaiao
