Identify 7 unknown substances!

What is this challenge about?

In this Take-Off Challenge, students become real forensic experts: They are given seven unknown white powders that they must identify using only simple tests—tasting is strictly prohibited.

The experiment can be conducted either as a challenge or as a standard lab assignment. The goal is to systematically examine the substances and use an evaluation table to determine which powder corresponds to which everyday substance, such as sugar, salt, or baking powder.

Rules

All groups receive the same seven numbered white powders (e.g. starch, baking powder, baking soda (sodium bicarbonate), salt, citric acid, chalk, sugar).
The substances must not be tasted; only observation and experimentation are allowed.
Only the specified tests are permitted: solubility, reaction with acid/base, iodine test and flammability.
Each group must carefully record its observations and, in the end, submit a clear identification for all seven numbers.
The winning team is the one that identifies all substances correctly in the shortest time.
If a team gives an incorrect answer, it receives a 3‑minute time penalty. During these 3 minutes, this team may not submit a new answer. The penalty ends either after the 3 minutes have elapsed or as soon as another team has submitted an answer.

Materials and preparation

Preparation:

Prepare 7 numbered samples with white substances for each team (e.g. starch, baking powder, sodium bicarbonate, salt, citric acid, chalk, sugar). The substances can all be ground into powder with a mortar so that they do not differ too much visually.

Materials per team:

• Several small cups (e.g. plastic shot glasses), test tubes or beakers
• Spoons or spatulas (e.g. teaspoons, wooden sticks)
• Pipettes
• 1 metal spoon (for the flammability test)
• Water
• Household vinegar (acidic solution)
• Bicarbonate solution (dissolve 1 tbsp sodium hydrogen carbonate in 100 ml water as a base)
• Iodine solution (e.g. Isobetadine from the pharmacy)
• Lighter for the flammability test
• Safety equipment: safety goggles, hair ties, possibly fire extinguisher or bucket of water
• Pen and paper for notes
• Evaluation table showing how the different substances behave in the tests (e.g. “bubbles with vinegar”, “turns blue with iodine”, “burns and turns brown”). The table can be downloaded here:

Challenge procedure:

Phase 1: Consultation period (approx. 5 minutes)
Before any testing, the teams receive the evaluation table and an overview of the materials. The goal of this phase is to develop a strategy instead of randomly “testing away”.
The groups read the table and think about which tests they want to perform and how.
They plan how to divide tasks within the group (e.g. pipetting, observing, recording).

Phase 2: Testing and analysis phase
Now it is time to experiment. The teams carry out the tests systematically so they can draw conclusions as quickly as possible:

• Solubility: Put a knife tip of white powder into 10–20 ml of water. Does the substance dissolve in water or does it remain as a sediment?
• Reaction with acid (vinegar): Add some vinegar to the powder. Does it fizz? If yes, carbon dioxide is produced – typical for carbonate or hydrogen carbonate salts.
• Reaction with base (bicarbonate solution): Is there gas formation with acidic substances such as citric acid?
• Iodine test: Dissolve the substance in a little water and add 1–2 drops of iodine solution. With starch, a characteristic blue to violet complex forms.
• Burning test: Place a small amount of powder on a metal spoon and heat it from above with the lighter. Organic substances such as sugar or starch turn brown or may smell caramel-like, whereas table salt, chalk or bicarbonate do not burn.

Important: The teacher should emphasize safety aspects (tie back hair, wear safety goggles, handle fire carefully, have extinguishing agents ready) and, if necessary, demonstrate the burning test themselves.
All observations are recorded in the table or in the notebook.
After a team has assigned a substance to each number, it can submit its results to the teacher. If the assignments are correct, that team is considered the winner. The remaining teams can continue experimenting.

Phase 3: Evaluation/discussion
Which method was the fastest? How did the winning team distribute tasks? Discuss together in class what you learned from this experiment.

Tips from our tests

• The iodine test can be omitted if necessary; the challenge also works using only solubility, acid/base reactions and the burning test.
• For classes with little lab experience, it can be helpful to demonstrate how to carry out the tests (especially the burning test) in plenary before the groups start themselves.
• Anyone wanting more variety can include additional harmless substances – the table must then be expanded accordingly. Other harmless substances include, for example: milk powder, washing powder, flour or cellulose (adapt the table accordingly).
• Additional test: pH paper or red cabbage indicator.

Background info:

The substances can be divided into organic and inorganic materials:

Organic substances (of plant origin):

• Sugar (sucrose)
• Starch
• Citric acid

Inorganic substances (mineral salts):

• Table salt (NaCl)
• Baking soda (NaHCO₃)
• Chalk (CaCO₃)

Baking powder is a mixture of baking soda, an acidifying agent and starch.

Learning objectives

Through this Take-Off Challenge, students learn to:

• Understand basic chemical properties of substances (solubility, flammability, acid–base reactions)
• Use simple detection reactions (e.g. iodine–starch reaction, gas formation with carbonates)
• Record observations systematically and evaluate them using a table
• Plan in a team, distribute tasks and develop a joint strategy

Afterwards, take a look together at how the Take Off candidates mastered this challenge: (released on 27.03.26).

Author: Joseph Rodesch (FNR)
Editor: Lucie Zeches (FNR)