You have been asked to carry out an investigation to test the following hypothesis: ‘The hotter the water, the more temporary hardness that will be removed.’ Gather the following equipment for use during your investigation:
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500 cm3 of hard water 500 cm3 of soft water Graduated cylinder Beaker(s)
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Soap flakes Mass balance Spatula
Tripod and gauze
3 Draw a labelled diagram of the set-up you will use. Write a step-by-step method.
Consider the following as you plan and carry out your investigation:
4 Identify the: a. Independent variable. b. Dependent variable. c. Controlled (fixed) variables.
5 What would be a suitable control for this investigation?
6 How much time will you need and what protective equipment will you need to wear?
7 Produce a suitable data collection sheet and comment on any trends that you see in your table of data. Construct an appropriate chart or graph to present your data.
8 Do your results indicate that your original hypothesis is false or not false? Do you need to change your hypothesis in light of the new information you gathered during this investigation?
9 Consider all sources of error and recommend potential adjustments to your method.
10 How do your results compare with those of your classmates? Is there evidence of trends within the class data set? How do your results compare with similar investigations online?
11 How might the results of your investigation be used to inform people living in hard water areas?
z Fig. 22.6.2 Limescale on a kettle element
12 What other physical, chemical and biological properties of water should local authorities consider monitoring before water is delivered to homes for human use?
