Week 5

Class 1: Mixtures

In science the word "pure" describes something

only containing a single substance. Pure water

contains just water, with no other substances

mixed with it.

A mixture is not pure. It is made up of

different kinds of particles that are

mixed together. The mixture may be of

elements, compounds or both. There are

solids, liquids and gases that are mixtures.

During the following classes, we will learn the difference between a mixture and a solution.

Mixtures and solutions are a common occurrence in our everyday lives. They are the air we breathe, the drinks and foods we consume, and the fabrics we clothe ourselves in. By studying how chemists distinguish pure substances from mixtures and solutions, you will start to appreciate how matter is organized at the atomic level. Knowing this, we can manipulate matter to improve our health and quality of life.

Then, you will solve the activity in the notebook:

1. Air is a mixture of different gases.

Look at the picture showing the gases

we can find in the air and:

a) Draw them

b) Write the formula for each one

c) Which ones are elements? how

can you tell?

d) Which ones are compounds?

e) Explain why air is a mixture, not

a compound.

2. The diagrams show the atoms in four different substances. Each circle represents an atom.

Complete the following table by drawing the diagrams representing the molecules:

3. In the picture we can see

some particles in air. The orange

circles represent oxygen atoms.

The blue circles represent nitrogen

atoms. The black circles represent

carbon atoms. The white circles

represent hydrogen atoms. Which is

the most common element in air? Which

is the least common compound?

4. Look at the lists of substances in the table. Write the list that only contains mixtures:

5. Write an example of a mixture that includes:

a) Solid - Solid

b) Solid - Liquid

c) Liquid - Gas

d) Liquid - Liquid

6. Alloys are mixtures. Give two examples of alloys

explaining the elements that were mixed and what is

the use of that alloy in real life.

When you add a spoonful of sugar or salt into

water it seems to disappear. This is called

dissolving (disolverse). You get a colorless

solution. The substance that dissolves is called

the solute. The substance that it dissolves into

is called the solvent.

A solution is a mixture. All solutions are transparent

or at least translucent (you can see through them),

this is why milk is not considered a solution, it is

opaque and you can not see through it.

Even if the solute seems to "disappear" in the solvent, it is still there, the molecules have simply spread out among the water molecules.

Today we will learn more about solutions as we solve some questions about them and at the same time, we create and then separate a salty solution:

Before you start solving this activity follow these instructions:

Measure 220 ml of water in the beaker
Add 2 spoons of salt
Stir the solution until the salt completely dilutes into the water
Put it on the stove at a high temperature
Once it starts boiling, measure the temperature of the water
Wait for as long as needed (you must see a change in the solution)

1) Mass is conserved when a solution is made. This means that to find the final weight of the solution you just have to add both weights. If we say a spoon of salt weighs 2.5 grams and 240ml of water weigh 240 grams, what is the weight of the solution you just created? (take into account that we used 2 spoons of salt, not one)

2) In this solution, which is the solvent, and which one is the solute?

3) When you add a solute into a solvent it dissolves, but if you keep adding more and more solute, there comes a point when no more of the solid will dissolve. You have made a saturated solution. Click on the image and follow the slides, then, answer the questions:

a) What happened when they heated up the saturated solution?

b) Which solution got saturated first, the one with sugar or the one with salt?

c) Which solute is more soluble in water? (This means you can add more of it before it gets saturated)

4) What happened at the end of the experiment with the solution you created?

5) What property was used to separate the solution? (What was the difference between the solute and the solvent that was useful to separate them?)

6) How could this knowledge be useful to a

person who has been shipwrecked (naufragado)

and finds himself/herself without water in the

middle of the ocean or on an island?

Check this link if you have no idea: LINK

7) Write one CONCLUSION from this

lab practice (What did you learn?)