The Nature of Matter
Elements, compounds and mixtures
Tell an element from a compound from a mixture, and say which of them can be taken apart by physical means.
A sprout salad and a spoonful of sugar syrup are both made by mixing. The difference is what you can see: the chopped onion and tomato stay visibly themselves, while the sugar vanishes into the water. In neither case has anything new been made — take the water away and the sugar comes back.
Three words worth separating
A mixture holds two or more substances that keep their own properties and do not react with each other. A pure substance holds one kind of particle. Pure substances come in two sorts: an element, which cannot be broken into anything simpler, and a compound, in which different elements have combined chemically in a fixed ratio to make something new.
Worked example
Iron filings and sulfur powder are stirred together. The same two are then heated together until a black mass forms. What is the difference between the two results?
Look at the stirred sample: black and yellow particles are still visible side by side, and a magnet pulls the iron out.
Both substances have kept their own properties, and one of those properties is enough to separate them again. That is a mixture.
Try it together
Electricity is passed through water that has had a few drops of dilute sulfuric acid added. Gas collects in two test tubes. Work out what the experiment shows.
A word or two for each answer.
1.A burning candle at the mouth of the first tube gives a pop sound. Which gas is that?
Have a go
Have a go on your own. A mixture of two or more metals, blended so evenly that the separate metals cannot be seen, has a name of its own. What is it? Give the one word.
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.