Topic 3 -Convalent Compounds And Separation Techniques

Question 1

When atoms make covalent bonds with one or more other atoms what to do they form ?

Answer 1

A Molecule

Question 2

Why do simple covalent compounds have a low melting point?

Answer 2

Due to the weak inter-molecular forces that only need a small amount of energy to break

Question 3

Why do simple covalent compounds not conduct electricity?

Answer 3

They have no free electrons or ions to carry the electric current.

(No mobile charge carrier)

Question 4

Why do ionic compounds have high melting points?

Answer 4

Due to the strong ionic bonds that need a lot of energy to break

Question 5

Why do ionic compounds not conduct electricity when solid and conduct electricity when melted or in a solution?

Answer 5

SOLID = Ions in fixed positions so no mobile charge carrier

MELTED= Ions are mobile and can carry the current

Question 6

What is Covalent bonding?

Answer 6

A shared pair of electrons between two atoms

Question 7

What are the two kinds of covalent substances?

Answer 7

1) simple molecular

2) giant molecular

Question 8

What are the two key points to do with diamond?

Answer 8

1) Each carbon atom forms FOUR covalent bonds in a giant covalent structure
2) It doesn’t conduct electricity because there are no free electrons

Question 9

Why is Diamond the hardest natural substance and what is it used for?

Answer 9

Due to the very rigid giant covalent structure.

It is used as cutting tools.

Question 10

What are the two key points to do with Graphite?

Answer 10

1) Each carbon atom only forms THREE covalent bonds leaving each atom with a delocalised electron
2) The sheets of carbon atoms are free to slide over each other and get rubbed off which is how pencils work.

Question 11

Why is Graphite a good conductor of electricity and what can it be used for?

Answer 11

It is a good conductor of electricity because the delocalised electron can carry the electric current which is why it can be used in electrodes.

Question 12

What are the three types of substances from Ionic and covalent bonding?

Answer 12

1) Ionic lattice
2) Simple molecular
3) Giant molecular

Question 13

What type of substance is sodium chloride if it conducts electricity when dissolved?

Answer 13

Ionic Lattice

Question 14

What type of substance is silicon (IV) oxide if it doesn’t conduct electricity and has a high melting&boiling point?

Answer 14

Giant Molecular

Question 15

What type of substance is Sucrose which doesn’t conduct electricity in a solution and has a low melting&boiling point and is soluble in water?

Answer 15

Simple Molecular

Question 16

what does Miscible mean and how is it separated?

Answer 16

When liquids DO mix together

They are separated by fractional distillation

Question 17

What does Immiscible mean?

Answer 17

When Liquids DON’T mix together

They are separated using a separating funnel

Question 18

What does a separating funnel do ?

Answer 18

The denser liquid sinks to the bottom of the funnel while the less dense liquid forms a layer on top.

The tap can be opened to drain off the denser liquid into a beaker Eg Oil & Water

Question 19

What does fractional distillation do?

Answer 19

Liquid air enters the column and is heated slowly. The remaining gases are separated using fractional distillation.

Question 20

Why in fractional distillation do the different liquids needs different boiling points?

Answer 20

So then the mixture is heated the different liquids will condense at different temperatures and be collected separately.

Question 21

What is chromatography?

Answer 21

A way of identifying substances in a mixture

Question 22

What does chromatography involve?

Answer 22

Spots of each mixture are placed at the baseline on some filter paper.
The paper is placed in solvent.
The solvent seeps up the paper taking the different chemicals in the sample away creating separate spots higher up.

Question 23

What is the equation to find out the Rf value for each chemical in chromatography?

Answer 23

Rf = Distance travelled by the substance / Distance travelled by the solvent