Question

• Fill half a beaker with water.
• Put a watch glass on the mouth of the beaker.
• Put few drops of ink on the watch glass.
• Now start heating the beaker. We do not want to heat the ink directly. You will see that evaporation is taking place from the watch glass.
• Continue heating as the evaporation goes on and stop heating when you do not see any further change on the watch glass.
• Observe carefully and record your observations.

1. What do you think has got evaporated from the watch glass?
2. Is there a residue on the watch glass?
3. What is your interpretation? Is ink a single substance (pure) or is it a mixture?

NCERT Class 9th Science Ch 2 Is Matter Around Us Pure

Answer 1

only water is evaporated and dye remains in the plate as residue. No ink is not a single substance its a mixture of water and dye colour

Answer 2

1) Water evaporates from the watch glass. This is because on heating water changes into its vapour state. The ink does not evaporate or sublime.

2) There is a residue on the glass in form of a bluish or violet color. This is ink that has precipitated and settled at the bottom of the watch glass.

3) Ink is not a single substance and not pure. Ink is a mixture and is formed by mixing water with a dye.