Chemistry - separation

Question 1

What are the 4 methods of separating mixtures by physical methods (physical methods means there are physical changes involved)?

Answer 1

Filtration
Evaporation
Chromatography
Distillation

Question 2

What methods are used for the separation of rock salt?

Answer 2

Filtration and evaporation

Question 3

What is rock salt?

Answer 3

A mixture of salt and sand

Question 4

In the experiment to separate rock salt you first of all grind it up in a pestle and mortar, what does this do?

Answer 4

This mixes the different solids together and releases all the salt from rocks

Salt is mined in the form of rock salt

Question 5

When you dissolve the mixture (rock salt) in water by stirring, what happens?

Answer 5

The salt dissolves into the water however the sand doesn’t dissolve and the sand is left at the bottom.

This difference allows us to separate them.

Question 6

Is sand soluble or insoluble?

Answer 6

Insoluble

Question 7

After dissolving, the next stage in separating rock salt is filtration, what is collected where?

Answer 7

The salt dissolved in the water passes through however the sand doesn’t pass through and stays in the filter paper

Question 8

Does the filter paper have holes in it?

Answer 8

Ye tiny holes you can’t see, the holes are too small to let the sand through

Question 9

How do you get the salt out of the solution?

Answer 9

You heat from below the mixture (which is in an evaporating dish) to allow evaporation to occur, leaving the salt in the dish

Question 10

During evaporation,what happens to the water?

Answer 10

It escapes the steam (gas) as the mixture is boiled

Question 11

What method separates liquids from solids?

Answer 11

Simple distillation

Eg. Salt and water

Question 12

How do you define a mixture?

Answer 12

2 or more substances jumbled up together

Question 13

What is the scientific name for a solid that dissolves?

Answer 13

Solute

Eg. In a salt solution the solute is the salt

Question 14

What is formed when a solute completely dissolves?

Answer 14

Solution

Question 15

What is the name of the liquid that does the dissolving?

Answer 15

Solvent

Eg. In a salt solution the solvent is the water

Question 16

If a solute dissolves in a solvent then it is…..?

Answer 16

Soluble

Question 17

If a solute doesn’t dissolve in a solvent, then it is ……?

Answer 17

Insoluble

Eg. Wax is insoluble in water

Question 18

If sand can’t dissolve in water it is X in Y?

Answer 18

X is insoluble

Y is water

Question 19

What is evaporation?

Answer 19

When a liquid changes into a gas

Question 20

Distillation is the method used to separate a soluble X from a Y?

Answer 20

X is solid

Y is liquid

Question 21

Condensation is ……

Answer 21

When a gas changes into a liquid

Question 22

Describe an example (everyday) of condensation?

Answer 22

When liquid drops form on a window, on the inside they have formed from the atmosphere.

Question 23

In the first step of distillation what is released from the heated flask?

Answer 23

Gas

Eg. If salt and water are the mixture , water vapour is released as gas

Question 24

How does the gas get to the top of the distillation tube (condenser)?

Answer 24

It rises with the heat

Question 25

What happens in the condenser (distillation tube)?

Answer 25

Gas is cooling and it turns into a liquid

Question 26

In a distillation experiment where is the salt near the end?

Answer 26

The salt is left behind in the flask

Question 27

The water collected is pure or dirty?

Answer 27

Pure because it’s been through the distillation process

Question 28

What does pure in chemistry mean?

Answer 28

Only contains one substance

Eg. Water only contains H20 molecules

Question 29

In a distillation experiment a thermometer is at the top of the flask, what temp will it show when water vapour (gas) is released?

Answer 29

100*C

Where water boils

Question 30

What is chromatography?

Answer 30

It is a separation technique based on the principle, that different substances will take different times to travel through the chromatography paper

Question 31

Name some uses of chromatography?

Answer 31

To see separation of mixtures

Eg. Dyes in ink, mixtures in blood, food colouring and additives

Question 32

The distance travelled by a chemical in chromatography is called what?

Answer 32

Retention factor (Rf)

Question 33

How is the (Rf) calculated?

Answer 33

Ratio of the Distance travelled by the sample spot against the distance travelled by the solvent front

Question 34

What is the equation for Rf value in chromatography?

Answer 34

Rf = distance moved by spot /

Distance moved by solvent front (liquid line)

Question 35

What is the base line in chromatography?

Answer 35

It is where the spot is placed (a pencil line can be drawn on the chromatography paper at the start)

Question 36

The Rf value is always less than 1

T or F?

Answer 36

T

Question 37

In chromatography experiments, is the base line above the line of liquid at the start?

Answer 37

Yes it’s above the liquid
When the paper is placed in the liquid the liquid solvent moves up through the base line and the substances to be separated move with it

Question 38

What should the baseline or start line be written in?

Answer 38

Pencil, not ink because it would smudge

Question 39

What happens to the solvent in chromatography?

Answer 39

It moves up through the chromatography paper

Question 40

How do you know if different substances are more soluble or less soluble (in chromatography)?

Answer 40

If there’re higher on the paper they are more soluble

Question 41

What happens when a substance dissolves?

Answer 41

A solute breaks into tiny particles and spreads through out the particles of a solvent

Question 42

In distillation why is a condenser able to cool a gas as it passes through?

Answer 42

Because it has cold water running on the outside