9.1 Solute, Solvent & Solution
Probe and Ponder
You’ve had ORS (Oral Rehydration Solution) when unwell. Have you noticed that every sip tastes the same — never salty in one mouthful and sweet in the next? Why is the taste so perfectly even?
When you stir sugar and salt into water, they spread evenly throughout — so every sip is identical. That’s a uniform mixture. Stir in chalk powder, sand or sawdust instead, and the bits don’t spread evenly — those are non-uniform mixtures.
The Three Names A uniform mixture like salt-or-sugar in water is called a solution. When a solid dissolves in a liquid:
- the solute is the substance that dissolves (the solid, e.g. salt),
- the solvent is the substance it dissolves in (the liquid, e.g. water),
- the solution is the uniform mixture they form.
\text{Solute} + \text{Solvent} \longrightarrow \text{Solution}
When two liquids mix
If a solution forms from two liquids, which is the solute and which the solvent? The rule is simple: the substance present in the smaller amount is the solute, and the one in the larger amount is the solvent.
Ever Heard Of… The Gulab Jamun Exception The chashni (sugar syrup) of gulab jamun has a large amount of sugar dissolved in a small amount of water. Even though there’s more sugar than water, the water is still the solvent and the sugar the solute — because here a solid (sugar) is dissolving in a liquid (water), and the solid is always the solute.
Science Talk Air is a uniform mixture of gases (Chapter 8). Does that make air a solution too? Talk it through: if “solution” just means uniform mixture, then a uniform mix of gases — or a gas dissolved in a liquid — should count. (You’ll see in 9.3 that oxygen dissolved in water is exactly such a solution.)