topic 3 - covalent compounds and separation techniques

Question 1

what do covalent bonds form between?

Answer 1

non-metals.

Question 2

what are covalent bonds?

Answer 2

a shared pair of electrons.

Question 3

why do atoms share electrons?

Answer 3

to get a full outer shell.

Question 4

why is there a lot of energy that is needed to break covalent bonds?

Answer 4

because they are strong.

Question 5

substances with covalent bonds often form what? and give an example?

Answer 5

molecules with low melting and boiling points like hydrogen and water.

Question 6

why do covalent bonds have low melting and boiling points?

Answer 6

because little energy is needed to break weak intermolecular forces.

Question 7

why do covalent bonds not conduct electricity?

Answer 7

because they do not have any free electrons or an overall electric charge.

Question 8

Give the properties of graphite?

Answer 8

it is a form of carbon in which the carbon atoms form layers.
the layers slide over each other, so graphite is much softer than diamond is.
used in pencils and as a lubricant.
each carbon atom in a layer is joined to only 3 other carbon atoms.
it conducts electricity.

Question 9

Give the properties of diamond?

Answer 9

it is a form of carbon in which each carbon atom is joined to 4 other carbon atoms forming a giant covalent structure.
very hard and has a high melting point.
used in cutting tools.
does not conduct electricity.

Question 10

what are immiscible liquids?

Answer 10

ones that don’t completely mix together.

Question 11

what are miscible liquids?

Answer 11

ones that mix together.

Question 12

what happens when 2 immiscible liquids are shaken together?

Answer 12

they will separate into layers.

Question 13

give an example of 2 immiscible liquids?

Answer 13

oil and water.

Question 14

what happens the the denser liquid and the less dense liquid in a separating funnel?

Answer 14

the more dense liquid sinks to the bottom, and the less dense liquid forms a layer on top.

Question 15

how are layers of immiscible liquids separated?

Answer 15

using a separating funnel and a tap.

Question 16

what happens when the tap is opened?

Answer 16

it drains off the denser liquid into a beaker.

Question 17

what does fractional distillation separate?

Answer 17

miscible liquids.

Question 18

the different liquids in F.D must have what?

Answer 18

different boiling points.

Question 19

what happens when the mixture of miscible liquids is heated in F.D?

Answer 19

the liquids will condense at different temperatures and can be collected separately.

Question 20

what is the method for separating out miscible liquids using F.D?

Answer 20

1. air is filtered to remove dust.
2. it is then cooled to -200 degrees and becomes a miscible mixture of liquids.
3. during cooling, water vapour condenses and is removed.
4. CO2 freezes and is removed.
5. the liquified air then enter F.D column and is heated slowly.
6. remaining gases are separated by F.D. Oxygen and argon come out together so another column is used to separate them.

Question 21

what is the definition of concentration?

Answer 21

measure of how much solute is dissolved in the solvent.

Question 22

what is the definition of soluble?

Answer 22

a substance which dissolves in a given solvent.

Question 23

what is the definition of solute?

Answer 23

a solid or a liquid that dissolves in a given solvent from a solution.

Question 24

what is the definition of solution?

Answer 24

a clear mixture that forms when a solute dissolves in a given solvent.

Question 25

what is the definition of solvent?

Answer 25

the liquid that dissolves the solute.

Question 26

what is chromatography used to find out?

Answer 26

which coloured compounds in a mixture contain.

Question 27

how does chromatography work?

Answer 27

some compounds work better in a solvent than others.
when a solvent moves along a strip of paper, it carries different substances at different speeds so they are separated.
the solvent is called the mobile phase.
the paper contains the stationary phase, through which the solvent and dissolved substances move.
the paper with separated components is called a chromatogram.

Question 28

how do I complete a chromatography experiment?

Answer 28

1. draw a pencil line 1cm from the bottom.
2. dot the dye onto the line.
3. place into a beaker, with the solvent touching the bottom of the paper, but not the dye.
4. cover and leave the solvent to move up the paper.
5. when the solvent nears the top, take it out and draw a line to where the solvent reaches.

Question 29

how can you work out the RF value?

Answer 29

from the value of the spots on a chromatogram.

Question 30

what is the RF value?

Answer 30

the ratio between the distance traveled by the dissolved substance and the distance travelled by the solvent.

Question 31

what is the formula for the RF value?

Answer 31

distance traveled by the substance / distance traveled but he solvent.

Question 32

what are RF values used in?

Answer 32

food industry and forensic science.

scientists use these values and refer to them to identify substances like food additives and drugs.