Covalent Compunds And Seperation Techniques

Question 1

What happens in a covalent bond

Answer 1

A pain of electrons is shared
The two atoms together become a molecule
It is between two non metals

Question 2

What are simple molecular covalent substances

Answer 2

There are very strong covalent bonds
But there are weak inter molecular forces
So the melting and boiling points are very low
Most molecular substances are liquid or gases at room temp
They don’t conduct electricity because their are no ions

Question 3

What are giant molecular covalent substances

Answer 3

They are similar to ionic lattices but there are no ions
All atoms are bonded by strong covalent bonds
They have high melting and boiling points
They don’t conduct electricity at all except from granite
They are insoluble

Question 4

Describe diamond

Answer 4

It is only made of carbon atoms
Each carbon atom forms four covalent bonds which makes it really hard
There are no free electrons so it doesn’t conduct electricity
It is really good as a cutting tool

Question 5

Describe graphite

Answer 5

Each carbon atom has three covalent bonds it creates sheets of carbon atoms which can slide over each other so graphite is a good lubricant
The layers are held really loosely so they can easily slide off that’s how a pencil works
There are lots of spare electrons so they can conduct electricity and granite can be used a electrodes

Question 6

What does immiscible mean

Answer 6

When the liquids don’t mix e.g. Oil and water

Question 7

What does miscible mean

Answer 7

When the liquids mix e.g. Milk and tea

Question 8

How do you separate immiscible liquids

Answer 8

Using a separating funnel
The denser layer sinks down
The tap is used to separate the two

Question 9

How do you separate miscible liquids

Answer 9

By fractional distillation

If they have different boiling points then the different liquids will condense at different layers

Question 10

What is chromatography

Answer 10

It is used to identify Substances in a mixture it works because different substances wash through wet filter paper at different rates

Question 11

How do you do chromatography

Answer 11

Put spots of each liquid on filter paper in a line
Roll up the paper and put it in a beaker containing a solvent the baseline must be above the water level
The solvent seeps up the paper taking the samples with it
Different chemicals in the sample form separate spots on the paper

Question 12

How to work out the Rf value

Answer 12

Distance travelled by substance/distance traveled by solvent

Question 13

Describe fractional distillation of liquid air

Answer 13

Air is filtered to remove dust
It is cooled to about -200 degrees and becomes a miscible mixture of liquids
The water vapour condenses and is removed during cooling
Carbon dioxide freezes and is removed
Oxygen and argon come out of the bottom of the fractional distillation column and nitrogen comes out of the top
Oxygen and argon are then separated