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Is Matter Around Us Pure? — Science STD 9 — Question

Gujarat BoardEnglish MediumSTD 9ScienceIs Matter Around Us Pure?4 Marks
Question
A, B and C are all liquids. Liquid A has a comparatively low boiling point. On heating, liquid a vaporizes completely without leaving behind any residue. Liquid A is being used increasingly as a fuel in motor vehicles either alone or by mixing with petrol. Liquid B has a very high boiling point. It also vaporizes completely on heating, without leaving any residue. Liquid B is a conductor of electricity and used in making thermometers. Liquid c has a moderate boiling point. On heating, liquid C vaporises leaving behind a white solid D which is used in cooking vegetables. The condensation of vapours from C give a liquid E which turns anhydrous CuSO4 to blue.
  1. Which liquid could be an element? Name this element.
  2. Which liquid could be a mixture? Name this mixture.
  3. Which liquid could be a compound? Name this compound.
  4. What could the solid D be?
  5. What do you think is liquid E?
✓

Answer

  1. Liquid B has a very high boiling point. It also vaporises on heating. It is a conductor of electricity and is used in making thermometers. So, B could be an element. Further, liquid B is mercury as mercury is a liquid metal, which expands on heating and is used extensively in thermometers.
  2. Liquid C has a moderate boiling point. It could be a mixture. It is a salt solution because when C is heated, it vaporises and leaves behind a white solid (salt), which is used in the process of cooking.
  3. Liquid A is used in motor vehicles as fuel, either alone or after mixing with petrol. It could be a compound because on heating, it does not leave any residue. It is alcohol as alcohol is being used in motor vehicles nowadays.
  4. Solid D is sodium chloride. It is also known as common salt and is added in food.
  5. Liquid E is water as, on heating, liquid C, which is a salt solution, leaves water vapours. On condensing these vapours, we obtain pure water. When water is mixed with anhydrous copper sulphate, we obtain a blue colour solution. This is because of the formation of hydrated copper sulphate solution.

$\text{CuSO}_4+5\text{H}_2\text{O}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ }\text{CuSO}_4\cdot5\text{H}_2\text{O}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {^\text{hydrated copper sulphate}}$

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