A, B and C are all liquids. Liquid A has a comparatively low boiling point. On heating, liquid A vaporises 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 vaporises 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.
(a) Which liquid could be an element? Name this element.
(b) Which liquid could be a mixture? Name this mixture.
(c) Which liquid could be a compound? Name this compound.
(a) 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 is mercury as mercury is a liquid metal, expands on heating and is used extensively in thermometers.
(b) Liquid C is a salt solution because when it is heated, it vaporises and leaves behind a white solid (salt), which is used in the process of cooking.
(c) Liquid A is used in motor vehicles as fuel, either alone or after mixing with petrol. Hence, it is alcohol as alcohol is being used in motor vehicles nowadays.
(d) Solid D is sodium chloride. It is also known as common salt and is added to food.
(e) 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.