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End of chapter exercises

Which of the following can be classified as a mixture:

  1. sugar

  2. table salt

  3. air

  4. iron

An element can be defined as:

  1. A substance that cannot be separated into two or more substances by ordinary chemical (or physical) means

  2. A substance with constant composition

  3. A substance that contains two or more substances, in definite proportion by weight

  4. A uniform substance

d.

A substance that cannot be separated into two or more substances by ordinary chemical (or physical) means

Classify each of the following substances as an element, a compound, a homogeneous mixture, or a heterogeneous mixture: salt, pure water, soil, salt water, pure air, carbon dioxide, gold and bronze.

Salt: Compound

 

Pure Water: Compound

 

Soil: Heterogeneous Mixture

 

Salt Water: Solution

 

Pure Air: Solution

 

Carbon Dioxide: Compound

 

Gold: Element

 

Bronze: Solution

Look at the table below. In the first column (A) is a list of substances. In the second column (B) is a description of the group that each of these substances belongs in. Match up the substance in Column A with the description in Column B.

Table 1

Column A

Column B

1. iron

A. a compound containing 2 elements

2. H 2 S

B. a heterogeneous mixture

3. sugar solution

C. a metal alloy

4. sand and stones

D. an element

5. steel

E. a homogeneous mixture

1) D

 

2) A

 

3) E

 

4) B

 

5) C

You are given a test tube that contains a mixture of iron filings and sulphur. You are asked to weigh the amount of iron in the sample.

  1. Suggest one method that you could use to separate the iron filings from the sulphur.

  2. What property of metals allows you to do this?

1) Extract the iron filings using a magnet

 

2) Magnetism

Given the following descriptions, write the chemical formula for each of the following substances:

  1. silver metal

  2. a compound that contains only potassium and bromine

  3. a gas that contains the elements carbon and oxygen in a ratio of 1:2

1) Ag

 

2) KBr

 

3) CO2

Give the names of each of the following compounds:

  1. NaBr

  2. Ba(NO 2 ) 2

  3. SO 2

  4. H 2 SO 4

1) Sodium bromide

2) Barium nitrate

3) Sulphur dioxide

4) Hydrogen sulphate (sulphuric acid)

Give the formula for each of the following compounds:

  1. iron (II) sulphate

  2. boron trifluoride

  3. potassium permanganate

  4. zinc chloride

1) FeSO4

2) BF3

3) KMnO4

4) ZnCl2

For each of the following materials, say what properties of the material make it important in carrying out its particular function.

  1. tar on roads

  2. iron burglar bars

  3. plastic furniture

  4. metal jewellery

  5. clay for building

  6. cotton clothing

Some suggestions for answers are given. Learners could discuss these questions amongst themselves.

 

1) High coefficients of friction

 

2) Inelastic, durable

 

3) Durable, easily cleaned

 

4) Shiny, malleable

 

5) Easily moulded while wet, strong and durable once dry

 

6) Fibrous, allows skin to “breathe”