Types of Mixtures - Emulsions, Alloys, Solutions, and Gels

The concentration formula is: $\text{Concentration (g/L)}=\frac{\text{mass of solute (g)}}{\text{volume of solution (L)}}$

The mass of solute (salt) is 15 g and the volume of solution is 0.5 L.

$\text{Concentration}=\frac{15}{0.5}=30\text{ g/L}$

The concentration is 30 g/L. This makes sense — dissolving 15 g into only 0.5 L (half a litre) gives a relatively concentrated solution.

We need to find the concentration in g/L by dividing the mass of solute by the volume of solution.

7.5 g/L would result from dividing 15 by 2, not by 0.5. This confuses multiplying by 2 with dividing by 0.5 — these are opposite operations.

0.033 g/L would result from dividing 0.5 by 15 — this reverses the numerator and denominator, which is incorrect.

15 g/L is simply the mass of solute with the g/L unit added on — it ignores the volume entirely and does not represent a concentration calculation.

$\frac{15\text{ g}}{0.5\text{ L}}=30\text{ g/L}$ The correct answer is 30 g/L.

Mayonnaise is a colloid (specifically an emulsion), and colloids have particles in the range of 1–1000 nm. Particles in this size range interact with visible light.

The Tyndall Effect describes how colloid particles scatter light that passes through them. When light hits the oil droplets in mayonnaise, it is scattered in all directions, making the mixture appear opaque and milky.

In a true solution, particles are smaller than 1 nm — too small to scatter visible light — so the solution appears transparent. This is why salt water is clear but mayonnaise is not.

The correct explanation is that oil droplets scatter light via the Tyndall Effect, making mayonnaise appear opaque.

We need to identify the correct physical reason why mayonnaise is opaque, relating to how light interacts with the mixture.

Emulsifiers such as lecithin are present in tiny amounts and do not absorb visible light. Their role is to stabilise the emulsion by sitting at the oil–water interface, not to block light.

Dissolved salt in vinegar forms a solution, which would appear transparent, not white. Dissolved ions are too small to scatter light and do not cause opacity.

This is the opposite of the truth. It is solutions whose particles are too small to scatter light. Colloid-sized oil droplets (100 nm–several micrometres) are exactly the right size to scatter visible light.

The correct answer is that oil droplets scatter light (Tyndall Effect), which is why emulsions like mayonnaise appear opaque.