Q1.
Gradually add a spoonful of salt into the glass tumbler and stir. Observe how many spoons of salt you can add before it stops dissolving completely. Record your observations in Table 9.1.
Answer
The first few spoons disappear completely. Somewhere around the sixth to the eighth spoon in half a tumbler of water (roughly 100 mL), the grains stop vanishing and a layer of salt stays at the bottom however long you stir. A typical filled Table 9.1 looks like this.
| Amount of salt taken (teaspoon) | Observation (salt dissolves / salt does not dissolve) |
|---|---|
| One | Salt dissolves completely — solution is unsaturated |
| Two | Salt dissolves completely — unsaturated |
| Three | Salt dissolves completely — unsaturated |
| Four | Salt dissolves, but takes longer stirring |
| Five | Salt dissolves with long stirring |
| Six | Most dissolves; a few grains remain |
| Seven | Salt does not dissolve — it settles at the bottom. Solution is now saturated |
Your own number may differ from seven, and it should. It depends on how much water you took, how big your spoon is, and how warm the room is — so record what you observe.
Why it happens: The water can hold only a fixed number of salt particles apart from one another at that temperature. Until that limit is reached each new spoonful is pulled apart and spread through the water. Once the limit is reached, any further salt simply stays as crystals — the solution has become saturated.
Tip: Use the same spoon, levelled off each time, and stir for the same length of time after every addition. Otherwise you are changing two things at once and the count means nothing.