Sample work Science Stage 5: Solving problems using practical chemistry
Work samples aligned to grades assist teachers to develop their understanding of the achievement standards at each grade level.
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.
- 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
- 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.
- 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
- Choose one step in this procedure and describe in detail the method and equipment Mollie could have used.
- Mollie’s deduction was incorrect. The sample contained manganese.
- Identify the step where the incorrect decision was made. Explain your answer.
- What should have been done at this step?
View the flow chart. (PDF 890.37KB)
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.
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.
Graded student work samples
Work sample feedback
Lesley
Lesley has demonstrated a very high level of competence in following a procedure to solve problems. A methodical approach has been taken, and the procedure and observations have been clearly presented in appropriate table format. A flow chart has been used to identify metal compounds and draw accurate conclusions from the data collected.
Critical thinking has been applied to solve problems, and the relationship between cause and effect has been explained. Lesley has demonstrated a very high level of competence in succinctly communicating information. This work sample demonstrates characteristics of work typically produced by a student performing at grade A standard.
Sam
Sam has demonstrated a high level of competence in following a procedure to solve problems. The procedure is detailed and accurate, and the observations have been clearly presented using an appropriate table format. A flow chart has been used to identify metal compounds and draw conclusions.
Critical thinking has been applied to solve problems, and the relationship between cause and effect has been explained, but some answers to the questions are a little confusing. This work sample demonstrates characteristics of work typically produced by a student performing at grade B standard.
Kim
Kim has demonstrated a high level of competence in following a procedure to solve problems. The procedure is detailed but lacks clarity in one step, and the observations have been presented in a simple but appropriate format. There are errors in the interpretation of the flow chart but the answers to the questions indicate a thorough understanding of the aim of the task and the results.
Kim has drawn conclusions from the data obtained and used this information to solve problems. This work sample demonstrates characteristics of work typically produced by a student performing at grade B standard.
Shannon
Shannon has demonstrated an adequate level of competence in using identified strategies and problem-solving skills. The method lacks some important details but has been adequately communicated using scientific language. Relevant conclusions have been drawn but a clear understanding of the aim has not been demonstrated, and the results have not been presented in an appropriate scientific format. This work sample demonstrates characteristics of work typically produced by a student performing at grade C standard.
Casey
Casey has demonstrated an adequate level of competence in using identified strategies and problem-solving skills. Information has been succinctly communicated but a scientific report format has not been used to present the procedure or results. Appropriate actions have been performed and relevant conclusions have been drawn but the critical analysis is superficial. This work sample demonstrates characteristics of work typically produced by a student performing at grade C standard.
Darcy
Darcy has demonstrated a limited level of competence in using identified strategies and problem-solving skills. A scientific procedure has been followed but some errors have been made in the method, and the observations have not been recorded in table format. Some reliable data has been obtained and basic conclusions have been drawn but the answers to the questions lack detail.
Darcy has demonstrated a basic understanding of scientific processes and limited skills in communicating using scientific terminology. This work sample demonstrates characteristics of work typically produced by a student performing at grade D standard.
Bailey
Bailey has demonstrated a limited level of competence in using identified strategies and problem-solving skills to plan and conduct a first-hand investigation. A procedure has been followed but there are some errors and omissions in the method, and the observations have been poorly recorded. Some reliable data has been obtained and basic conclusions have been drawn. There is some evidence of recall of information about ionic substances but a lack of understanding of their composition.
Bailey has demonstrated a limited level of competence in communicating using an appropriate scientific format. This work sample demonstrates characteristics of work typically produced by a student performing at grade D standard.
Bobby
Bobby has demonstrated a very limited level of competence in using identified strategies and problem-solving skills. The flow chart has been used to identify two different metal compounds but a scientific procedure has not been followed. The observations have been poorly recorded and a very limited level of competence in drawing conclusions and communicating findings has been demonstrated. This work sample demonstrates characteristics of work typically produced by a student performing at grade E standard.
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