Example 1
A filter reduces cloudiness from 60 units to 15 units. What change is supported?
Cloudiness decreased by 60−15=45 units under the tested conditions. These measurements alone do not establish removal of microbes or dissolved salt.
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Year 7
Reading separation results
Read before-and-after data and identify what different separation stages remove.
Method and worked examples
Water may contain suspended solids, dissolved substances and microorganisms. Ordinary filtration can remove sand without removing dissolved salt. Clear water is therefore not automatically pure or drinkable. Settling, filtration and distillation target different material properties; read the named component rather than assuming every stage removes everything.
In a table, a reduction equals the starting value minus the final value. If cloudiness falls but salt concentration stays unchanged, suspended material was reduced while dissolved salt remained. Filtering sand from salt water leaves a salt solution as the filtrate. Distillation can then collect water by condensation while retaining most non-volatile salt. Keep the desired product clear at every step.
Example 1
Example 2
A filter removes sand but the dissolved salt concentration is unchanged. Which method matches the result?
Ordinary filtration: sand is trapped, while dissolved salt passes through with water.
Watch out: Invisible dissolved substances and microorganisms may remain. Safety requires suitable validated treatment and testing.