Cloudy water that will not clear

The idea

Heavier suspended particles settle on standing and filtration removes only larger ones, so very fine suspended particles that keep a liquid cloudy need centrifugation or coagulation.

Muddy water after a rain

You leave muddy water to stand. The mud settles, but the water still looks cloudy. You pour it through a cotton cloth.

Will the water now be clear?

• Often not. Tiny particles remain
• Yes, always perfectly clear
• It will turn into a solution

Settle it, then filter it

Let muddy water stand. Then try filtering it. Is it clear?

Why settling and filtering are not always enough

Heavier suspended particles settle when the mixture is left standing, and filtration removes only the larger particles. Very fine suspended particles keep the liquid cloudy, so we need centrifugation or coagulation.

You can filter muddy water through a cotton cloth or filter paper. Some larger particles are removed, but the water often remains cloudy.

Notes

Heavier particles settle and filtration removes larger particles. Very fine suspended particles keep water cloudy: use centrifugation or coagulation.

Check yourself

Muddy water is left to stand. What settles first?

Why may the water still be cloudy after filtering?

Which techniques can clean water when filtering is not enough?

Filtration removes…

• The smallest particles. The fine ones stay suspended longest.
• Nothing can settle. Heavier particles settle.
• The heavier mud particles — correct. Yes.
• Very fine particles pass through — correct. Yes.
• Filter paper adds mud. The tiny particles are the cause.
• The water has turned into oil. Water does not change like that.
• Sublimation and deposition. Those are for solids that turn to vapour.
• Centrifugation and coagulation — correct. Yes.
• Crystallization only. That separates dissolved solids.
• only the larger suspended particles — correct. Yes.
• every particle, however fine. Fine particles can still pass.
• only dissolved particles. Dissolved particles pass through.