العلوم (بالإنجليزية) الصف الخامس الابتدائي، الأسبوع 12: Mixtures everywhere

Heat, melting and mixtures

الأسبوع 12 · المحور الثاني «المادة والطاقة»، الوحدة الثانية «حركة الجسيمات»، المفهوم 2.3 «مقارنة تغيرات المادة» (ب): تغير الحالة والمخاليط · 3 دروس

Mixtures everywhere

Discovery Education Science P5: Term 1, Unit 2, pp. 189–191

GoalSay what a mixture is, give examples, and describe ways to separate the parts of a mixture.

New words

mixture · two or more materials put together that do not change each otherseparate · to take the parts of a mixture apartfilter · to hold back solid bits while a liquid passes through

Explanation

A mixture is made of two or more parts that are only mixed together. Each part keeps its own properties. Sugar is still sweet when it is stirred into tea, and pebbles are still pebbles in a bucket of sand. A salad, a bag of mixed nuts, sea water and the air are all mixtures. The air is a mixture of gases that we cannot see, while in the nuts we can pick out each kind. Because the parts do not change, we can separate a mixture by physical means. We can pick pieces out by hand, shake a mixture through a sieve, filter a muddy liquid so the mud is held back, or let water evaporate so that dissolved salt is left behind. A compound is different: its parts join to make a completely new substance that is hard to pull apart.

Mixture	Parts	Way to separate
mixed nuts	different nuts	pick out by hand
sand and pebbles	sand, pebbles	shake through a sieve
muddy water	water, mud	filter
salt water	water, salt	let the water evaporate

Worked examples

A bowl of salad has cucumber, tomato and onion. They are only mixed together, so each piece keeps its own colour, shape and taste. We can pick every kind out again.

At a building site a worker shakes sand mixed with small stones through a sieve. The sand falls through the holes and the stones stay on top. This is a physical way to separate a mixture.

Salt water is left in a dish in the sun. The water evaporates into the air, and white salt crystals stay in the dish. The salt was in the water all along, but it did not change. Nobody tastes it.

Class activity

Mix and unmix (a grown-up helps). Mix rice, lentils and small pasta in a bowl. Separate them by hand, then try a kitchen sieve. Next stir a spoonful of salt into a cup of warm tap water, pour a little onto a dark plate and leave it in a sunny place for a day or two. Write what is left on the plate. Never taste it.

Practice

Is a bag of mixed nuts a mixture? Give a reason.

Which method would you use to separate pebbles from sand?

The water in beaker A is muddy. Which would you use to take out the mud: a sieve or a filter? Say why.

Sugar is stirred into tea and seems to disappear. How can you tell that the sugar did not change into something new?