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

Rajasthan 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 $CuSO_4$ 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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