Chemistry 11–12 · Year 12
Le Chatelier's principle with the cobalt(II) chloride and chloride equilibrium: concentration and temperature
Module 5: Equilibrium and Acid Reactions
Teacher-led demonstration
A teacher carries out this activity as a demonstration. Its materials, steps, variables, misconceptions and sources are not published on the open web, and neither is any result, control or note that states a number or an amount: tutors and administrators read them on the learning platform, with the safety card first. The idea, the hazards and the curriculum references are below.
Open the procedure on the learning platform (tutor or administrator sign-in)
School laboratory, not for home
In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
The idea
When an equilibrium is disturbed by adding a reactant or by heating, the position shifts to oppose the change; the direction of the colour change reveals the sign of the enthalpy change.
Safety card
Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
Hazards
- cobalt(II) chloride is toxic, a sensitiser and a classified carcinogen
- concentrated hydrochloric acid is corrosive and fumes
- hot water
Controls
- technician prepares the mixture in a fume cupboard
- teacher demonstration: only the teacher handles the tubes and the concentrated acid, in a fume cupboard or with strong ventilation
- gloves and eye protection for the teacher; eye protection for learners, who observe from their benches
- all cobalt solutions returned for disposal as hazardous waste
Note
It states a number or an amount, which may be part of the method, so it is shown with the method to tutors and administrators on the learning platform.
What you should see
Adding water turns the mixture pink (hexaaquacobalt(II) ion favoured as chloride is diluted); adding concentrated hydrochloric acid turns it blue (tetrachlorocobaltate(II) favoured). Heating turns it blue, cooling turns it pink, and the cycle repeats, so the forward reaction is endothermic. The predicted effect of adding solid sodium chloride is a shift towards blue, because it adds chloride ions. The changes take only seconds.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document)CH12-12CH11/12-4CH11/12-5
- Chemistry 11-12 Syllabus (2025), NESA; implemented from 2028, not yet taughtCH-12-01CH-12WS-04CH-12WS-05
- Australian Curriculum v9No Australian Curriculum v9 code is listed.