Diffusion, Dissolving & Separating Mixtures

Question 1

Define a ‘mixture’.

Answer 1

A combination of two or more substances that are not chemically joined together and can be separated by physical means

Question 2

What is a ‘pure substance’?

Answer 2

A substance consisting of only one type of particle (atom or molecule)

Question 3

Define ‘solubility’.

Answer 3

A measure of how much of a solute can dissolve in a given amount of solvent at a specific temperature

Question 4

What is a ‘solute’?

Answer 4

The solid substance that is dissolved into a liquid

Question 5

What is a ‘solvent’?

Answer 5

The liquid in which a solute is dissolved to form a solution

Question 6

Define a ‘saturated solution’.

Answer 6

A solution in which no more solute can be dissolved at that particular temperature

Question 7

What does ‘insoluble’ mean?

Answer 7

A substance that cannot be dissolved in a particular solvent

Question 8

What is a ‘dilute solution’?

Answer 8

A solution containing a small amount of solute relative to the amount of solvent

Question 9

What is a ‘concentrated solution’?

Answer 9

A solution containing a large amount of solute relative to the amount of solvent

Question 10

Give an example of a common mixture found in nature.

Answer 10

Seawater or air

Question 11

What is the primary purpose of filtration?

Answer 11

To separate an insoluble solid from a liquid

Question 12

Name the key pieces of equipment used in a filtration setup.

Answer 12

Filter paper, filter funnel, and a beaker/conical flask

Question 13

In filtration, what is the ‘residue’?

Answer 13

The solid trapped in the filter paper

Question 14

In filtration, what is the ‘filtrate’?

Answer 14

The liquid that passes through the filter paper

Question 15

Why are there tiny holes in filter paper?

Answer 15

They are small enough to let liquid molecules through but too small for larger solid particles

Question 16

Can filtration separate salt from water? Why?

Answer 16

No, because the salt is dissolved (it is a solute), and its particles are small enough to pass through the filter paper

Question 17

What is the correct way to fold filter paper for a funnel?

Answer 17

Fold it in half, then in half again to form a cone

Question 18

Why should you moisten the filter paper before pouring the mixture?

Answer 18

To help it stick to the sides of the funnel and prevent the mixture from bypassing the paper

Question 19

Why is it important not to overfill the filter paper?

Answer 19

To prevent the solid-liquid mixture from flowing over the edge and into the filtrate

Question 20

Give a real-world application of filtration.

Answer 20

Coffee machines or water treatment plants

Question 21

What is the purpose of evaporation in separation?

Answer 21

To separate a soluble solid (solute) from a liquid (solvent) by turning the liquid into gas

Question 22

Name the equipment needed for a basic evaporation experiment.

Answer 22

Evaporating dish, Bunsen burner, tripod, and gauze

Question 23

What happens to the solvent during evaporation?

Answer 23

It gains thermal energy and changes state from liquid to gas (vapor)

Question 24

What is left behind after all the water has evaporated from a salt solution?

Answer 24

Salt crystals

Question 25

What is 'crystallisation'?

Answer 25

The process of forming solid crystals from a saturated solution as the solvent evaporates

Question 26

How do you obtain large crystals during evaporation?

Answer 26

By evaporating the solvent slowly at a lower temperature

Question 27

When should you stop heating the solution for best crystal formation?

Answer 27

When crystals first start to form around the edge (at the crystallisation point)

Question 28

Why might you use a water bath instead of direct heating for evaporation?

Answer 28

To prevent the solid from spitting (decrepitation) or decomposing from too much heat

Question 29

What is the difference between evaporation and boiling?

Answer 29

Evaporation happens only at the surface at any temperature; boiling happens throughout the liquid at a specific boiling point

Question 30

What is the risk of "spitting" during evaporation?

Answer 30

Hot solid particles can fly out of the dish, causing burns or loss of product

Question 31

What two main substances make up "Rock Salt"?

Answer 31

Sodium chloride (salt) and sand/grit

Question 32

Why is rock salt crushed with a mortar and pestle first?

Answer 32

To increase the surface area, making it dissolve faster in water

Question 33

Why is the crushed rock salt added to water and stirred?

Answer 33

To dissolve the salt while leaving the sand as an insoluble solid

Question 34

Is it better to use hot or cold water to dissolve the salt? Why?

Answer 34

Hot water, as salt dissolves more quickly and effectively in higher temperatures

Question 35

In the rock salt practical, which substance is the filtrate?

Answer 35

The salt-water solution

Question 36

In the rock salt practical, which substance is the residue?

Answer 36

The sand left in the filter paper

Question 37

What is the order of the four stages in this practical?

Answer 37

1. Crushing, 2. Dissolving, 3. Filtering, 4. Evaporating

Question 38

Why is the salt obtained from this method usually white, even if the rock salt was brown?

Answer 38

The brown impurities (sand/dirt) are removed during the filtration stage

Question 39

How could you prove the residue is sand?

Answer 39

It will not dissolve in water even after stirring and heating

Question 40

Why is it important to wash the residue in the filter paper with a little extra water?

Answer 40

To ensure any trapped salt solution is washed through into the filtrate

Question 41

What safety gear is essential when heating mixtures?

Answer 41

Safety goggles and a lab coat

Question 42

Why should you use a heatproof mat?

Answer 42

To protect the laboratory bench from heat damage

Question 43

What should you do if the evaporating dish begins to spit?

Answer 43

Turn off the Bunsen burner or move it away safely

Question 44

Why must you wait for equipment to cool before touching it?

Answer 44

To avoid thermal burns; hot ceramic and glass look the same as cold ones

Question 45

How do you calculate the mass of salt recovered?

Answer 45

Mass of dish with salt - Mass of empty dish

Question 46

If you started with 10g of rock salt and recovered 3g of salt, what percentage was salt?

Answer 46

30%

Question 47

What is an 'impurity' in a substance?

Answer 47

An unwanted substance mixed with the desired product

Question 48

How does an impurity affect the melting point of a substance?

Answer 48

It usually lowers the melting point and makes it melt over a range of temperatures

Question 49

IGNNORE THIS: It usually lowers the melting point and makes it melt over a range of temperatures[

Answer 49

IGNORE THIS: Tap water contains dissolved minerals (impurities) that would contaminate the results

Question 50

What is the 'Law of Conservation of Mass' in the context of mixtures?

Answer 50

The total mass of the mixture is equal to the sum of the masses of the individual components before mixing