Page 237 - Chemistry ICSE Class IX
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Chemistry Practicals 225
Observations
The observations made in this experiment are summarised below:
Ŷ Ŷ Ŷ
Behaviour of the Two Water Samples Towards Soap Solution
SAMPLE A: Temporary hard water SAMPLE B: Permanent hard water
Before boiling #HVGT $QKNKPI CPF ſNVGTKPI
5CORNG # 5CORNG $ 5CORNG # 5CORNG $
No lather with soap No lather with soap Gives lather with soap Does not give lather
solution. solution. solution. with soap solution.
Gives curdy precipitate Gives curdy precipitate No curdy precipitate Gives curdy precipitate
with soap solution. with soap solution. with soap solution. with soap solution.
Results and Conclusions
The following conclusions are derived from the above observations:
y Initially, both the samples showed hardness.
y After boiling, sample A gives lather with soap solution, whereas sample B does not give lather with
soap solution.
This shows that the hardness of sample A is removed by boiling, whereas that of sample B is not removed.
Thus,
y The original sample A is temporary hard water.
y The original sample B is permanent hard water.
Explanation
Temporary hardness is due to the presence of bicarbonates of calcium and magnesium in water. On boiling,
bicarbonates decompose to give carbon dioxide and the corresponding carbonate. Carbonates of calcium
and magnesium are insoluble in water. Carbon dioxide escapes out of the water, and the carbonates of
calcium and magnesium settle down in the form of precipitate. The precipitate is removed by ltration. The
ltrate is the soft water.
EXPERIMENT 6.3
Objective
6Q UQHVGP VGORQTCT[ CPF RGTOCPGPV JCTF YCVGT D[ VJG CFFKVKQP QH YCUJKPI UQFC
Apparatus Required
Beakers (2), Test tubes
Materials Required
Samples of temporary and permanent hard water, Washing soda, Filter papers, Soap solution
