Micelles remove oily dirt

The idea

In water, soap molecules form clusters called micelles, with hydrophobic tails inside around the oily dirt and ionic ends facing outside; this forms an emulsion, so the dirt is pulled into the water and rinsed away.

Oil that will not wash off

Oil does not dissolve in water. Yet soap and water can wash an oily cloth clean.

How do you think soap pulls oily dirt into the water?

• Soap molecules gather around the oil with their ionic ends facing the water
• The oil changes into water
• The soap melts the oil

Soap around oil

Press Next step.

A micelle carries the oil

The tails hold the oil from inside the cluster. The ionic ends touch the water, so the whole cluster can be washed away.

In water, soap molecules form clusters called micelles, with the hydrophobic tails inside around the oily dirt and the ionic ends facing outside. This forms an emulsion, so the dirt is pulled into the water and rinsed away.

Notes

In water, soap molecules form micelles, with hydrophobic tails inside around the oily dirt and ionic ends outside. This forms an emulsion, so the dirt is pulled into the water and rinsed away.

Check yourself

In a micelle, where are the hydrocarbon tails of soap molecules?

Which part of the soap molecules faces the water in a micelle?

What is the cluster of soap molecules around oily dirt called?

What does the soap micelle do to the dirt?

• Outside, facing the water. The ionic ends face outside, towards the water.
• Dissolved in the water, away from the dirt. The tails are inside the cluster, around the oily dirt.
• Inside, around the oily dirt — correct. Yes!
• The ionic ends — correct. Yes!
• The hydrocarbon tails. The hydrocarbon tails point into the oily dirt.
• The oil droplet. The oil droplet is in the centre of the micelle, not facing the water.
• An ester. An ester is a compound formed from an acid and an alcohol.
• A micelle — correct. Yes!
• A catalyst. A catalyst causes a reaction to occur or proceed at a different rate.
• Turns it into water. The dirt is not changed into water. The micelle pulls it into the water.
• Dissolves it by itself without the soap. Oil does not dissolve in water. The micelle holds the dirt and pulls it into the water.
• Pulls it into the water so it can be rinsed away — correct. Yes!