Elements,Compunds and mixtures

Question 1

What is chemical composition?

Answer 1

Different substances can serve different functions as
they have different properties.

This is due to their chemical composition.

Chemical composition is the chemical components
that make up a substance.

Matter can be classified as elements, compounds and
mixtures according to their chemical composition.

Question 2

What are elements?

Answer 2

An element is a substance that cannot be broken
down into 2 or more simpler substances by
chemical methods.Matter in its simplest form is called an element.

Thus, elements are the basic building blocks of all
matter.

Elements can occur naturally on their own as solids,
liquids or gases.

They can also combine with other elements.

Question 3

How are elements studied?

Answer 3

Scientists have classified all the discovered
elements into a table called the Periodic Table.

This enables us to study the elements in a more
systematic way as they are classified according to
their chemical properties.

Question 4

What is the difference of a metal and non metal is terms of appearance?

Answer 4

Appearance

Metal: Shiny (lustrous)

Non-metal: Dull (non-lustrous)

Question 5

What is the difference between a metal and non-metal in terms of Physical state?

Answer 5

Physical state at
r.t.p.

metals: Mostly solids (except
mercury)

Non-metals: Gases, volatile
liquids or solids

Question 6

What is the difference between a metal and non-metal in terms of Melting and boiling points?

Answer 6

Melting and
boiling points

metals:High (except for
sodium, potassium and
mercury)

non-metals:Low (except for
carbon and silicon)

Question 7

What is the difference between a metal and non-metal in terms of Ductility

Answer 7

Ductility

metals:• Ductile (can be
drawn into wires)

non-metals:Brittle if solid

Question 8

What is the difference between a metal and non-metal in terms of Malleability?

Answer 8

Malleability

Metals:• Malleable (can be
hammered into
different shapes
without breaking
• Sonorous (makes a
ringing sound when
struck)

non-metals:Brittle if solid

Question 9

What is the difference between a metal and non-metal in terms of Heat Conductivity?

Answer 9

Heat
conductivity

metals:Good

non-metals:Poor (except carbon in
the form of graphite and
diamond)

Question 10

What is the difference between a metal and non-metal in terms of Electrical conductivity?

Answer 10

Electrical
Conductivity

metals:Good

non-metals:Poor (except carbon in
the form of graphite)

Question 11

What are the properties and uses of aluminium?

Answer 11

Aluminium

Properties:

Silvery, shiny

Low density

Malleable

Corrosion resistant

Uses:

Aluminium foils

Aluminium drink cans

Aircraft bodies (aluminium alloys)

Question 12

What are the properties and uses of copper?

Answer 12

Copper

Properties:

Reddish brown solid

Good conductor of electricity

Ductile

Uses:

Copper wires

Copper pipes

Question 13

What are the properties and uses of chlorine?

Answer 13

Chlorine

Properties:

Greenish yellow gas

Bleaches dyes

Poisonous

Uses:

Bleaching of clothes

To kill bacteria in drinking water

and swimming pool water

Question 14

what are the properties and uses of Iodine?

Answer 14

Iodine

Properties:

Black crystals

Poisonous

Antiseptic (prevents wound infections)

Uses:

As antiseptic in medicines

Question 15

How are elements represented?

Answer 15

Chemists use chemical symbols to represent
elements.

Each symbol is unique, consisting of one or
two letters.

The names and symbols of all known elements are found
in Periodic Table.

Question 16

What are atoms?

Answer 16

An element is made up of tiny particles called atoms.

Atoms are the smallest particles of an element that have
the chemical properties of that element.

The atoms of an element are different from that of another
element.

Question 17

What are molecules?

Answer 17

A molecule is a group of two or more atoms that
are chemically bonded (joined together).

Diatomic molecules are those that
are formed by the chemical bonding
of two atoms.

E.g. hydrogen (H2) oxygen (O2)
nitrogen (N2)

Question 18

What are polyatomic molecules?

Answer 18

Polyatomic molecules consists of four or more

atoms that are chemically bonded together.

Question 19

what is a compound?

Answer 19

A compound is a substance that is made up of 2 or
more elements chemically combined in a fixed
ratio.
Water is a compound made up of the elements
hydrogen and oxygen.

However, water does not share the same properties
as its constituent elements.

For example, water exists as a liquid at room
temperature but its elements exist as gases.

Question 20

What are the examples of compounds around us?

Answer 20

Table salt

Elements in the
compound: sodium
and chlorine

Sugar

Elements in the
compound: carbon,
oxygen and hydrogen

Chalk

Elements in the
compound: calcium,
carbon and oxygen

Question 21

What is the first property of a compound?

Answer 21

The properties of a compound are usually different from the
elements it is made up of.

Example — table salt (sodium chloride)

Sodium chloride is
a white solid used in
cooking.

Sodium is a soft,
silvery and highly
reactive metal.

Chlorine is a
yellowish-green
poisonous gas.

Question 22

What is the second property of a compound?

Answer 22

The elements that make up a compound are always
combined in a fixed proportion by mass.

For example, sodium and chlorine always combine
chemically in the ratio of 1:1 to form table salt
Hence, the ratio of sodium to chlorine by mass is
fixed.

Question 23

what is the third property of a compound?

Answer 23

A compound cannot be broken down by physical
methods. This is because a compound is made up of
different elements that are chemically combined.
For example, sodium and chloride cannot be
separated by physical methods such as filtration.

Question 24

How are compounds seperated?

Answer 24

A chemical reaction is necessary to separate the
elements in a compound.

Compounds can also be broken down by using electricity.

This process is known as electrolysis.

Question 25

What are mixtures?

Answer 25

A mixture consists of two or more different substances | that are mixed but not chemically combined.

Question 26

what are some examples of mixtures around us?

Answer 26

Some examples of mixtures around us: A mixture consists of two or more different substances that are mixed but not chemically combined. Milk Milk is a mixture of compounds such as proteins and fats. Air Air has the properties of a mixture. For example, inhaled air contains more oxygen than exhaled air.

Question 27

What are mixtures made up of?

Answer 27

Mixtures may be made up of: elements; compounds; or both elements and compounds. The components of a mixture may or may not exist in the same state of matter. For example: a liquid-liquid mixture: vinegar, made of ethanoic acid and water; and a solid-liquid mixture: sugar cane juice, made of sugar in water.

Question 28

What is the first property of a mixture?

Answer 28

A mixture has the properties of the substance it is made up of. -Air has the properties of the gases it is made up of. -Air supports combustion because the oxygen gas in air supports combustion. -Air turns limewater chalky because the carbon dioxide in air reacts with the limewater.

Question 29

What is the second property of a mixture?

Answer 29

The components of mixtures are not mixed in any fixed proportion. -For example, the proportion of the gases that make up the air may vary with place and time. -The air in the city contains a higher amount of carbon dioxide than the air near the sea.

Question 30

What is the third property of a mixture?

Answer 30

When a mixture is formed, no chemical reaction occurs. Hence, a mixture can be easily separated by physical methods. -For example, air is formed by simply mixing the gases it is made up of. -The gases do not react with one another and thus, can be separated using physical methods.

Question 31

What is the difference betwene a mixture and compound in terms of seperation?

Answer 31

``` The components of a mixture can be separated by physical processes such as magnetic separation, filtration or distillation. ``` ``` A compound can only be broken down into its elements or into simpler compounds by chemical processes (e.g. thermal decomposition or electrolysis). ```

Question 32

What is the difference betwene a mixture and compound in terms of Properties?

Answer 32

The chemical properties of a mixture are the same as those of its components. The physical and chemical properties of a compound are different from those of its constituent elements.

Question 33

What is the difference betwene a mixture and compound in terms of Formation

Answer 33

No chemical reaction takes place when a mixture is formed — usually there is little or no energy change. ``` A chemical reaction takes place when a compound is formed — usually there is an energy change, e.g. the reactants get hot or cold. ```

Question 34

What is the difference betwene a mixture and compound in terms of composition

Answer 34

The components of a mixture can be mixed in any proportion. The elements in a compound are always combined in a fixed proportion.

Question 35

What is an alloy?

Answer 35

An alloy is a mixture of metals with other elements (usually metals but sometimes non-metals such as carbon). Alloys are widely used and in great demand because they tend to be stronger than pure metals. An alloy is an example of a mixture.