C1.7a Thermal decomposition of carbonates: Student brief Practice Controlled Assessment This practice controlled assessment is about the decomposition of carbonates. Carbonates decompose when they are heated, producing calcium oxide and carbon dioxide. Carbon dioxide can be detected using limewater. When the carbon dioxide is passed through it the limewater turns milky. You are going to test the hypothesis that some metal carbonates decompose more easily than others when they are heated. Plan an investigation to test what happens when different metal carbonates are heated.
Part A: Planning How to attempt the task: You must produce a plan. The plan must include: •
an explanation of which equipment you need to complete the task. You may want to draw a diagram of how the equipment will be set up
•
which variable (or variables) you will change and which you will keep the same
•
which measurements you should make to test the hypothesis, explaining how these will test the hypothesis, and including the number and range of measurements
•
any risks that are linked to the practical task and how you can reduce these to make your practical task safer
You should check the overall plan is clear and will produce a range of results that will test the hypothesis.
Part B: Observations You are going to test the hypothesis that some metal carbonates decompose more easily than others when they are heated. You will test this hypothesis using your own method from Part A. You should also collect some secondary evidence on the decomposition of metal carbonates.
How to attempt the task: You should decide on the number and range of measurements you will make. Complete the practical task, recording your measurements clearly and accurately. Collect some secondary evidence on this task. Comment on the quality of the source of this secondary evidence.
Part C: Conclusions You will need your primary and secondary evidence from the Part B: Observations task and information about the method you used.
How to attempt the task: You must process your primary and secondary evidence from Part B and present these, using mathematical processes if relevant. You must produce a conclusion in which you: •
review all of the primary and secondary evidence, then identify and deal with any anomalies
•
draw conclusions from this processed evidence to prove or disprove a hypothesis
•
show how the data supports the conclusion
•
explain how you might change the method if you were going to repeat the investigation
•
describe the primary and secondary evidence you might collect to extend your investigation and say why you would collect it.
© Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
C1.7b Thermal decomposition of carbonates: Observations Practice Controlled Assessment You are going to investigate what happens when different metal carbonates are heated. You will be given the following equipment/resources: eye protection, 25 cm3 measuring cylinder, 3 × boiling tubes, 3 × delivery tubes with bungs, 3 × spatulas, 3 × test tubes, balance, Bunsen burner, heatproof mat, stand, boss and clamp, stop clock, teat pipette, test tube rack, limewater (IRRITANT), calcium carbonate (powdered), copper carbonate (powdered) (HARMFUL), zinc carbonate (powdered)
Health and safety Eye protection should be worn. Limewater is an IRRITANT. Copper carbonate is HARMFUL. To avoid suck-back, it is essential to remove the delivery tube from the limewater before removing the Bunsen. Follow these instructions when carrying out the practical: 1
Measure 1 g of a metal carbonate into a test tube.
2
Clamp the test tube at about 45°. The bottom of the test tube should be high enough off the bench to allow a Bunsen burner to be used under it safely.
3
Put a boiling tube into the test tube rack, and add 20 cm3 of limewater using the measuring cylinder.
4
Put the end of a delivery tube into the limewater and fit the bung into the test tube. Adjust the apparatus if necessary to make sure everything fits safely.
5
Using a blue flame, heat the metal carbonate through the end of the test tube. Start the stop clock at the same time as you start heating. Observe the limewater and the metal carbonate.
6
When the limewater becomes too milky for you to see the end of the delivery tube, or when two minutes have passed, remove the delivery tube to avoid the limewater being drawn up. Stop heating and stop the stop clock. Allow the apparatus to cool.
7
Repeat steps 1 to 6 using clean apparatus and each of the other metal carbonates. Repeat for any of the metal carbonates if needed.
© Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
C1.7c Thermal decomposition of carbonates: Recording results Practice Controlled Assessment Name
Class
Date
Carry out the investigation on Worksheet C1.7b Thermal decomposition of carbonates: Observations and use this sheet to record your results and draw a conclusion.
Recording your results 1
Record your measurements and observations in this table.
Time taken for limewater to turn milky (s) Name of metal carbonate
Experiment 1
Experiment Mean 2
Observations
Presenting data 2
a What is the range in times taken for the limewater to turn milky? b If you repeated an experiment, calculate the mean time for each carbonate.
3
Draw a bar chart on the graph paper below. Put the metal carbonate used on the x-axis and the time (or mean time) on the y-axis. You will need to label both axes and add numbers and units to the yaxis.
Š Pearson Education 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
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C1.7c Thermal decomposition of carbonates: Recording results
Practice Controlled Assessment
Considering your results/conclusions 4
5
a
Which carbonate decomposed most easily? Give reasons for your answer.
b
Which carbonate decomposed least easily? Give reasons for your answer.
c
Write the names of the carbonates in order of how easily they decomposed. Start with the one that decomposed quickest.
Other than by looking for the production of carbon dioxide, how could you tell that zinc carbonate and copper carbonate decomposed when heated?
Evaluation 6
a If you did your experiments more than once, how repeatable were your results for each metal carbonate?
b Compare the results you obtained with the results from other groups. How similar were the results? Suggest reasons for any differences seen between your results and their results.
7
Think about the method you used to compare how quickly the carbonates decompose. How could it be improved? Explain why each improvement would help to make your results more repeatable.
Š Pearson Education Ltd 2010. Edexcel GCSE Science Activity Pack This document may have been altered from the original.
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