Topic 5 (elements, compounds and mixtures)

Question 1

Which elements are monatomic?

Answer 1

Only the noble gases such as helium and neon

Question 2

What is a compound?

Answer 2

Two or more elements chemically joined together with different properties than its constituent elements.

Question 3

Are compounds considered pure substances?

Answer 3

Yes

Question 4

What are the differences between a mixture and a compound?

Answer 4

In a mixture, the constituents are not in fixed ratios but in a compound, the constituent elements are in the same fixed ratio
Mixtures melt and boil over a range of temperatures. Compounds have a fixed melting and boiling point
Properties of a mixture are the same as its constituents, but properties of a compound are different from properties of constituents.
Mixtures can be separated by physical methods, compounds must be separated by chemical methods.

Question 5

What is a homogeneous mixture?

Answer 5

A mixture that is uniform in appearance. Also called a solution

Question 6

What is a heterogeneous mixture?

Answer 6

A mixture where you can see the boundaries between the components.

Question 7

What are alloys?

Answer 7

Alloys are mixtures of metals with other elements. They tend to be stronger than pure metals.

Question 8

What elements are steel, brass and bronze made of?

Answer 8

Steel is 99% iron, 1% carbon
Brass is 70% copper, 30% zinc
Bronze is 90% copper, 10% tin

Question 9

What is the difference between a physical and chemical change?

Answer 9

After a physical change, no new substance is formed. After a chemical change, new substances are formed.

Physical changes are reversible, but chemical changes are usually irreversible.

Question 10

Are these changes physical or chemical?
-Magnetising an iron bar
-Iron rusting
-Melting ice
-Milk souring
-Dissolving salt

Answer 10

Magnetising an iron bar is physical
Iron rusting is chemical
Melting ice is physical
Milk souring is chemical
Dissolving salt is physical

Question 11

What is a combination reaction?

Answer 11

A reaction where two or more substances react to form a compound.

Question 12

What is a decomposition reaction?

Answer 12

A reaction where a substance breaks down into simpler substances

Question 13

What is a combustion reaction?

Answer 13

A reaction where a substance is heated with oxygen to release a lot of heat

Question 14

What are indicators of a chemical change?

Answer 14

-Production of effervescence
-Colour change
-Temperature change
-Formation of precipitate