Solving Problems using Practical Chemistry
| Grade | Work Samples |
|---|---|
| End of Stage 5 (end of Year 10) | |
| Grade A | Lesley |
| Grade B | Sam Kim |
| Grade C | Shannon Casey |
| Grade D | Darcy Bailey |
| Grade E | Bobby |
Description of activity
Students apply their understanding of chemical reactions involving precipitation in a first-hand investigation and solve problems to identify unknown metal compounds in solution. A flow chart is used, together with the information provided (see Additional Information), to identify the metal compound dissolved in a solution.
Part A: Students are provided with a solution containing an unknown chemical. They follow the flow chart to select appropriate reagents and conduct simple tests to identify the unknown chemical. Each student records his/her results and conclusions in an experimental report. During this activity, the students will be observed by the teacher to assess the accuracy of their procedure.
Part B: Students attempt to solve the following three problems.
(I) Pairs of metal compounds in solution are listed below. For each pair describe in one sentence a reaction that would distinguish between them.
- Chromium and nickel
- Silver and tin
- Sodium and potassium
- Barium and calcium
(II) A chemical bottle with a torn label is found on a shelf in the chemical store. The laboratory assistant thinks the compound might be zinc chloride. Describe how the laboratory assistant could determine the answer.
(III) Mollie performed a chemical group analysis on an unknown compound. She decided that the unknown substance was aluminium. This is how she recorded her procedure:
“A solution was made by dissolving part of the sample in water. After adding some ammonium chloride solution and ammonia solution, it was heated. There looked as if there was a white precipitate present.”
Questions:
(a) Choose one step in this procedure and describe in detail the method and equipment Mollie could have used.
(b) Mollie’s deduction was incorrect. The sample contained manganese.
(i) Identify the step where the incorrect decision was made. Explain your answer.
(ii) What should have been done at this step?
Context
Students have previously performed similar investigations using the flow chart and chemical group analysis tasks in their classwork. Students are given two hours to complete parts A and B. They are provided with the relevant risk assessments.
Areas for Assessment
Outcomes
A student:
5.7 relates properties of elements, compounds and mixtures to scientific models, theories and laws
5.14 undertakes first-hand investigations independently with safety and competence
5.15 gathers first hand information accurately
5.19 uses critical thinking skills in evaluating information and drawing conclusions
5.21 uses creativity and imagination in the analysis of problems and the development of possible solutions
Criteria for assessing learning
(These criteria would normally be communicated to students with the activity.)
Students will be assessed on their ability to:
- follow a procedure to perform an investigation
- process the information gathered from an investigation
- use cause and effect relationships to explain ideas
- predict outcomes relating to the observations made and draw conclusions
- apply information and critical thinking to solving problems.