Q1.
What do you observe? (after swirling until the added salt dissolves)
Answer
The reading on the balance does not change. Before swirling, the pan carries water plus a heap of undissolved salt; after swirling it carries a clear salt solution — and the number on the display is the same.
Mass of water taken (50 mL) ≈ 50.0 g
Mass of salt added (one spatula) ≈ 2.0 g
Expected mass of solution = 50.0 g + 2.0 g = 52.0 g
Mass actually read after dissolving = 52.0 g (within ±0.1 g)
Mass of salt added (one spatula) ≈ 2.0 g
Expected mass of solution = 50.0 g + 2.0 g = 52.0 g
Mass actually read after dissolving = 52.0 g (within ±0.1 g)
So mass of solution = mass of water + mass of salt. Dissolving a solid in water is a physical change, and no mass is gained or lost in it.
Why it happens: the salt has not gone anywhere. Its Na⁺ and Cl⁻ ions have simply spread out among the water molecules instead of sitting stacked in a crystal. Every particle that was on the pan before is still on the pan. Nothing has been added, nothing has escaped — so the balance cannot read anything different.
Try This: repeat with a sheet of paper. Weigh it, tear it into small pieces on the pan, weigh again. Same reading. Tearing changes the shape and size of the pieces, not the amount of matter.