In order to complete the task, the students must have previously learned about the reaction of sodium bicarbonate (baking soda) with citric acid and how to interpret it. The task can be worked through on a purely experimental level or else with prior knowledge of chemistry. The students should definitely have the basic idea that gases formed in a closed container generate pressure.
Degree of difficulty of the task: medium.
The teaching methods provide teachers with all the important information on using the worksheet of the same name and the related incremental hints in class. The scientific background on the task and possible variations are provided.
The five incremental hints for the task are provided with the corresponding answers. They are also available as a separate ready-to-print medium named “Foam fire extinguisher (hints for printing)” or as an interactive medium named “Foam fire extinguisher (interactive hints)” on the media portal of the Siemens Stiftung.

Foam fire extinguisher (hints for printing) (Text)
Foam fire extinguisher (interactive hints) (Interaktiv)
Foam fire extinguisher (task) (Text)
Tasks with incremental hints – An introduction (Text)

Chemistry; Physics

Grade 5 to 6; Grade 7 to 9; Grade 10 to 13

Middle/high school

Chemical reaction; Gas; Pressure (physics)

Siemens Stiftung Media Portal

Dr. Lutz Stäudel (text), Dieter Arnold (photo) and MediaHouse GmbH

© Siemens Stiftung 2017