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20 cm³ samples of waters, A, B, C and D, are tested for hardness by adding soap solution and shaking the mixture - Edexcel - GCSE Chemistry - Question 1 - 2016 - Paper 1
Question 1
20 cm³ samples of waters, A, B, C and D, are tested for hardness by adding soap solution and shaking the mixture. The soap solution is added until a permanent lather... show full transcript
Worked Solution & Example Answer:20 cm³ samples of waters, A, B, C and D, are tested for hardness by adding soap solution and shaking the mixture - Edexcel - GCSE Chemistry - Question 1 - 2016 - Paper 1
Step 1
(i) Which of the water samples is most likely to be pure water?
Answer
The water sample that is most likely to be pure water is sample A. This is because it requires only 0.1 cm³ of soap solution to form a permanent lather both before and after boiling. A low volume of soap solution indicates that there are no hardness ions present.
Step 2
(ii) Which water sample is most likely to contain only temporary hardness?
Answer
Water sample B is most likely to contain only temporary hardness. This is indicated by the decrease in the volume of soap solution required to form a permanent lather after boiling, from 5.0 cm³ before boiling to 2.0 cm³ after boiling. This reduction suggests that the hardness present in sample B is temporary and can be removed by boiling.