Split the Mixture

Why it matters

Your sister accidentally tips sand into a glass of clean water, and salt into another. You cannot just pick the bits out by hand, so how do you get each one back?

Predict first

You have sand mixed in water. The sand does not dissolve. What is the easiest way to separate the sand from the water?

The right method depends on the mixture. An insoluble solid like sand is caught by filtration, a dissolved solid like salt is recovered by evaporation, and iron can be pulled out with a magnet.

• Boil the water away until only sand is left
• Pour it through filter paper — correct
• Bring a magnet near it
• Add more water

What you do

Drag each mixture to the BEST method for separating it.

Check yourself

Filtration is used to separate a mixture when one substance is:

Filter paper traps solid particles that do not dissolve while the liquid passes through. So filtration removes an insoluble solid from a liquid.

To get pure salt back from salt water, the best method is:

The salt is dissolved, so it will not stay on filter paper. Heating evaporates the water and leaves the dissolved salt behind.

Which method would separate iron filings from a mixture of iron filings and sulphur powder?

Iron is magnetic but sulphur is not, so a magnet attracts and pulls out the iron filings, leaving the sulphur behind.

• An insoluble solid in a liquid — correct
• A solid fully dissolved in the liquid
• Two gases mixed together
• Two liquids that mix completely
• Evaporation of the water — correct
• Filtration through filter paper
• Using a magnet
• Adding more salt
• Bring a magnet near the mixture — correct
• Filter the dry mixture through paper
• Evaporate it
• Let it sublime