2.2 Pure substances and mixtures

• Scheikunde
• Middelbare school
• havo, vwo
• Leerjaar 2

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substance property or not?

property

not a property

inflamable

colour

Temperature

phase

Mass

shape

Density

melting point

Volume

Tekst

Pictogrammen

corrosive

toxic

explosive

environmentally dangerous

harmful, irritant

inflamable

Drag the substance to the substance property

nice smell

strong

light

see through

elastic

sweet

acidic

inflamable

rubber

glass

soap

steel

vinegar

alluminium

sugar

wood

H2.2 Pure substances and mixtures

learning objectives

• You can distinguish between pure substances and mixtures.
  
• You can explain what a molecule is and the types of molecules that make up pure substances and mixtures.
  
• You can distinguish between solutions and suspensions.
  
• You can describe how substances can be separated by extraction or filtration.
  
• You can explain the function of alcohol as a solvent.

Introduction

Most substances you encounter at home are mixtures.

You can see this immediately when you look at the packaging of a food or medicine.

It lists the various substances contained in the product. These substances are called ingredients.

'pure spring water'

A bottle of spring water might say "pure spring water" is inside. However, spring water isn't pure. It contains all sorts of dissolved substances, as you can see on the label. The word "pure" in this case means the water isn't contaminated with hazardous substances or bacteria. You can drink it without risk to your health.

pure substance

You'll find only a few pure substances in your home. An example of a pure substance is granulated sugar. A packet of sugar contains only sugar; it doesn't contain any other substances. Table salt is also a pure substance, at least if no iodine has been added (figure above).

with added iodine          pure salt

mixture

Ice tea consists of several substances, which we call a mixture.

Types of mixtures

Different types of mixtures:

- Solution

- Suspension

Solution = clear

solid, liquid, or gas in a liquid solvent

molecules are mixed together

Recognizing solutions

Solutions are always clear. You can see right through them. 

Water is clear and colorless, even if you've dissolved sugar or salt in it.

A solution can have a color. Tea or iced tea are good examples.

Solutions also always stay well-mixed. If you leave a bottle of soda in the cupboard for a year, it will remain well-mixed.

Suspension = cloudy

Solid substance dissolved in a liquid

Recognizing suspensions

If a mixture is cloudy (opaque), it may not be a solution but a suspension.

Paint, for example, is not a solution, but a suspension: a liquid containing a finely dispersed powder.

Paint separates; over time, the powder settles to the bottom of the can.

Which statement is true?

1. A pure substance consists of more than one substance
2. A pure substance consists of exactly one substance
3. Some pure substances consist of one substance, some of more

a suspention is a..

1. Mixture of two liquids
2. Mixture of two solids
3. Mixture of a liquid and a solid
4. a pure substance

Are the sentences correct or incorrect?
I A solution is always clear.
II A suspension is transparent.

1. both are correct
2. I is incorrect II is correct
3. I is correct II is incorrect
4. both are incorrect

Make the sentence complete.
You filled a bottle with lemonade. After half a day, you see that the lemonade still looks the same as when you filled the bottle.
The lemonade is a ……………………...

Extracting

Separation by using a difference in solubility of solids

Filtration

Separating solids from liquids

This can be done with a suspension

Filter

Residue - remains in the filter

Filtrate - passes through the filter

Which of the following drinks do you make by extraction?

1. limonade
2. water
3. tea
4. cola

What is the filtrate when making coffee with a coffee maker?

1. the ground coffee that you scoop from the package into the filter
2. the hot water dripping on the ground coffee
3. freshly brewed coffee in the pot under the filter
4. the coffee grounds that remain in the filter

What have you learned today?

You may now try the following

Assignments C2.2: 2, 3, 5, 6, 7

The rest is automatically your homework.