Solution, colloid, suspension
Put salt in one glass of water. Put chalk powder in another. Put drops of milk in a third. All three look mixed.
Loading lab…
The rule
A solution has the smallest pieces and a suspension has the largest. A colloid lies in between. Size decides what the tests show.
1 nm (a nanometre) is one billionth of a metre. The pieces of a solution are under 1 nm. A colloid has pieces of 1 to 1000 nm. A suspension has pieces over 1000 nm.
| Test | Solution | Colloid | Suspension |
|---|---|---|---|
| Size of pieces | Under 1 nm | 1 to 1000 nm | Over 1000 nm |
| Looks cloudy or grainy | No | Often | Yes |
| Settles if left | No | No | Yes |
| Caught by filter paper | No | No | Only the big pieces |
| Torch beam shows a path | No | Yes | Yes |
Filter paper has holes about 10,000 nm wide. Only pieces bigger than that stay on the paper. Fine pieces of a suspension can pass through. So muddy water can stay cloudy.
Salt in water is a solution. Milk and fog are colloids. Muddy water and chalk in water are suspensions.
A colloid looks even, but it scatters light. So it counts as heterogeneous.
Watch out!
Passing through filter paper does not mean something dissolved. Milk goes through the paper. Milk is a colloid, not a solution.