Water tests and domestic water treatment
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 worked examples, 6 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- From river to tap
- Chemical tests for water
- A warning
Read the transcript of the teaching part
Last time
Before we start: last time, in The reactivity series, displacement and extraction, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
From river to tap
The water that comes out of your tap was once a river or a reservoir, with mud, leaves and microbes in it. How do chemists know that a liquid is water? And how does a water works turn dirty river water into something safe to drink, using only a few simple steps?
Chemical tests for water
Anhydrous copper(II) sulfate is a white powder. When water is added, it turns blue. Anhydrous cobalt(II) chloride, or cobalt chloride paper, is blue. When water is added, it turns pink. Both are chemical tests for water. They show that water is present.
A warning
These tests only show that water is present. Tap water, sea water and orange juice all give a positive result. They do not show that the water is pure. The copper sulfate has the formula CuSO 4. The blue form is CuSO 4 dot 5H 2 O, and 36 percent of its mass is water.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Chemical tests for water · Treatment of domestic water · Tests for gases and water · Water treatment.
The whole chapter: Chemistry of the Environment, Experimental Techniques and Chemical Analysis, Chemistry of the Environment.
Chapter 10: Chemistry of the environment
- Clean air and photosynthesis 6 min
- Air pollutants, catalytic converters and global warming 5 min
- Water tests and domestic water treatment 5 min
Also for IGCSE Chemistry 0620
Which topics come up most in IGCSE Chemistry 0620 past papers, counted from every paper since 2004.