Topic 3 - Covalent Compounds And Separation Techniques

Question 1

What is formed with a covalent bond?

Answer 1

Molecule

Question 2

What are the two types of covalent structures?

Answer 2

Giant molecular covalent

Simple molecular covalent

Question 3

What are the properties of a simple molecular bond?

Answer 3

Weak forces of attraction between molecules

Low melting and boiling points because of ^

Don’t conduct because no free electrons

Question 4

What are the properties of a giant molecular covalent bond?

Answer 4

No charged ions

Strong covalent bonds

Very high melting and boiling points due to ^

Don’t conduct (except graphite)

E.g diamond and graphite

Question 5

Why is diamond used in saws?

Answer 5

4 strong bonds extremely hard.

Question 6

Why is graphic used in pencils?

Answer 6

Layer rubs off and leaves a line.

Question 7

Properties of graphite?

Answer 7

3 strong bonds

Conducts

Layers Sea of delocalised electrons between layers.

Good lubricant because layers slide over each other

Question 8

What is a covalent bond?

Answer 8

Share pair of electrons

Question 9

draw a dot and cross diagram of water

Answer 9

Question 10

what does miscible mean?

Answer 10

it mixes with other liquids

Question 11

what does immiscible mean

Answer 11

it doesn’t mix with other liquids

Question 12

how do you separate two immiscibile liquids?

Answer 12

let two immisclible substances are shaken together and left to stand they will separate into diffferent layers.

the denser liquid goes to the bottom.

put them in sparating funnel with a tap. the tap can be opened to drain off the denser liquid.

for example oil and water can be separtated this way.

Question 13

how do you sperate miscible liquids?

Answer 13

fractional distalation however they have to have different boiling points. air is filtered to remove dust. it’s then cooled to -200* during cooling water vapour condenses and is removed. then CO_{2 .}

liquidfied air then enters the column and is heated slowly. the remaining gases are sperated using fractional distilation but argon and oxygen come out together so another column us used to separate them.

Question 14

how do you do chromatography?

Answer 14

you put a line in pencil near the bottom of the chromatograph. then but spots of each mixure being tested on it. roll up the paper and put it in a beaker containing a solvent such as water. make sure the pencil line is above the solvent. the solvent seeps up the paper taking the samples with it. different pigments will form different spots.

Question 15

How do you work out Rf values of substances from a chromatograph?

Answer 15

distance traveled by substance/distance travelled by solvent.