Question

What will be the residue left on the watch glass on heating blue ink in it?

Answer 1

Hint : We know that blue ink is a mixture of blue or black color dye in water. So there is a volatile and a non-volatile component, so we use the process which helps us to separate the volatile component from non-volatile components.

Complete Step By Step Answer:
The process in which a volatile component is separated from a non-volatile component is known as evaporation. Evaporation is one type of vaporization reaction, in this process the mixture in which the compounds have different boiling points are heated. As the temperature increases the compound having low boiling point evaporates.
Put a watch glass on the top of a beaker and put a few drops of ink on the watch glass. Now start heating the beaker using a Bunsen burner, after some time we can notice the evaporation taking place in the watch glass. Continue heating as the process of evaporation goes on and stop when you can observe no further change on the watch glass. Now we can observe that the residue is left behind on the watch glass and the water has evaporated. In this way evaporation is used to separate the volatile component from non-volatile components.
Therefore, the residue left on the watch glass is the solute dye. Due to heating of the ink the water solvent in the ink evaporated leaving behind the dye, the solute.

Note :
Remember that the wind moving over the surface can carry the vapours during the process of evaporation so this point should be taken care of while separating two liquids. And we should heat the mixture slowly and stop the process when one of the components evaporates.