C1b 5.3 Everyday Emulsions

What happens if you let ice cream melt and then re-freeze it?

Separates into crunchy ice crystals and a buttery oily part

Made from two runny liquids!

Egg yoke stops the oil and water from separating outEgg yoke is an emulsifier

Oil, water

mayonnaise

milkice cream

salad dressing

What do these substances have in common?

They are all……

OK – so what is an emulsion?

Emulsions are foods made from a mixture of oil and water and they are important foods as they are smooth and creamy.

But, oil and water don’t mix (immiscible) so we need a special substance which stops the water and oil separating out.

Oil droplet

Water

We need an EMULSIFIER

Emulsifiers stop oil and water from separating out, but how do they work?

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An emulsifier molecule

This end is attracted to water (Hydrophilic)

This end is attracted to oil (Hydrophobic)

oil droplet

The charged oil droplets repel each other (like charges repel), keeping them spread throughout the water.

water

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The negative charges repel each other which stops the oil droplets from coming together and forming bigger drops.

Observing an emulsion (milk) with a microscope

Put a drop of one type of milk in the centre of the microscope slide.

Place a cover slip at the edge, and support it with the mounted needle.

Gently, lower onto the liquid in order to minimise air bubbles getting trapped underneath.

Put the slide onto the microscope stage, and adjust for the lowest magnification and bring into focus. Repeat for other milk.

Draw diagrams of what you see.