C3 Pure and Impure Substances

Question 1

Define element

Answer 1

A substance made of only one type of atom.

Question 2

Define (chemical) compound

Answer 2

Substance made of more than one type of atom chemically bonded together.

Question 3

Define (chemical) molecule

Answer 3

Two or more atoms, chemically bonded into a single particle.

Question 4

Does a molecule have to be a compound?

Answer 4

No, a molecule can be an element made of more than one of the same type of atom chemically bonded together into a single particle.

Question 5

Define (chemically) pure

Answer 5

When a substance is made of only one element or compound.

Question 6

Define (chemically) impure

Answer 6

When a substance is made of more than one element or compound, or a mixture of elements and compounds.

Question 7

What is a mixture?

Answer 7

An impure substance that can be separated by physical (not chemical) processes.

Question 8

Is spring water pure? Explain your answer.

Answer 8

No. Spring water contains minerals, as well as water molecules which are not chemically bonded.

Question 9

Is air pure? Explain your answer.

Answer 9

No. Air contains a mixture of elements and compounds in their gaseous state which are not chemically bonded.

Question 10

State one similarity and one difference between boiling and evaporation?

Answer 10

Similarity: both a state change from liquid to gas
Difference: Evaporation can occur at any temperature, boiling occurs at the boiling point of the substance.

Question 11

Define dissolve

Answer 11

When a substance is added to a solvent (liquid) and its particles spread out evenly within the liquid.

Question 12

Define solute

Answer 12

A solid or gas that dissolves in a solvent.

Question 13

Define solvent

Answer 13

A liquid that dissolves a solute

Question 14

Define solution

Answer 14

A mixture made when a solute dissolves in a solvent.

Question 15

Define solubility

Answer 15

The mass of a solute that will dissolve in a given volume of solvent

Question 16

Define insoluble

Answer 16

A substance that does not dissolve in a liquid.

Question 17

Define soluble

Answer 17

A substance that does dissolve in a liquid (solvent).

Question 18

What is a saturated solution?

Answer 18

A solution where no more solute will dissolve in the solvent.

Question 19

Generally, what is the effect of increasing the temperature on solubility?

Answer 19

The greater the temperature, the greater the solubility

Question 20

What piece of equipment could be used to separate marbles from sand, and what physical property does it separate them based on?

Answer 20

Sieve. Based on the size of the object.

Question 21

What physical property does filtration separate substances based on?

Answer 21

Size of particles

Question 22

What word could be used to describe the solubility of sand in water?

Answer 22

Insoluble

Question 23

What is the name of the substance left in the filter (paper) after filtration?

Answer 23

Residue

Question 24

What is the name of the substance that passes through the filter (paper)?

Answer 24

Filtrate

Question 25

What types of substances are most commonly separated by filtration in chemistry?

Answer 25

Insoluble solids from liquids

Question 26

What types of substances are most commonly separated by evaporation in chemistry?

Answer 26

Soluble solids from liquids

Question 27

What is crystallisation?

Answer 27

Slow evaporation that allows crystals to form.

Question 28

What physical property does chromatography separate substances based on?

Answer 28

Solubility

Question 29

What is chromatography used to separate?

Answer 29

Pigments (colours) in a solution.

Question 30

Which part of the simple chromatography set-up is considered the stationary phase?

Answer 30

The paper.

Question 31

Which part of the set-up above is considered the mobile phase?

Answer 31

The solution moving up the paper.

Question 32

What formula can be used to calculate the retention factor (Rf) of the pigment?

Answer 32

Rf = Distance moved by pigment / Distance moved by solvent

Question 33

Calculate the Rf value of red pigment which has moved 2cm when the solvent has moved 10cm on a chromatogram.

Answer 33

Rf= 2/10 = 0.2

Question 34

Calculate the Rf value of the purple pigment which has moved 6cm when the solvent has moved 10cm on a chromatogram.

Answer 34

Rf= 6/10 = 0.6

Question 35

What is the piece of paper with separated pigments called, once chromatography is complete?

Answer 35

Chromatogram

Question 36

What process can be used to separate two liquids based on their boiling points?`

Answer 36

Distillation

Question 37

What is the state change that occurs in the round bottomed flask during simple distillation?

Answer 37

Boiling or evaporation (liquid to gas)

Question 38

What is the state change that occurs in the condenser during simple distillation?

Answer 38

Condensing (gas to liquid)

Question 39

What does desalination mean?

Answer 39

To remove salt from salt water (sea water)

Question 40

Why do we not use desalination to produce drinking water in the UK?

Answer 40

Very energy intensive. No need as we have a good supply of clean drinking water.

Question 41

Fractional distillation separates out a range of different chemicals based on their…

Answer 41

Boiling points.

Question 42

Give two mixtures that are commonly separated using fractional distillation.

Answer 42

Air and crude oil

Question 43

What scale is used to represent how acidic or alkaline something is?

Answer 43

pH scale

Question 44

What is the pH of a neutral substance?

Answer 44

7

Question 45

What is the pH of an acidic substance?

Answer 45

Less than 7

Question 46

What is the pH of an alkali substance?

Answer 46

More than 7

Question 47

How could you describe a substance of pH 8

Answer 47

(Weak) Alkali

Question 48

How could you describe a substance of pH 2

Answer 48

(Strong) Acid

Question 49

How could you describe a substance of pH 5

Answer 49

(Weak) Acid

Question 50

How could you describe a substance of pH 14

Answer 50

(Strong) Alkali

Question 51

What is the standard word equation for a reaction between an acid and an alkali?

Answer 51

Acid + Alkali → Salt + Water

Question 52

What type of salts are formed by hydrochloric acid?

Answer 52

Chloride salts

Question 53

What type of salts are formed by sulfuric acid?

Answer 53

Sulfate salts

Question 54

What type of salts are formed by nitric acid?

Answer 54

Nitrate salts

Question 55

Give the word equation for the reaction between copper oxide and sulphuric acid

Answer 55

Copper oxide + sulfuric acid → copper sulphate + water

Question 56

Give the word equation for the reaction between sodium hydroxide and hydrochloric acid

Answer 56

sodium hydroxide + hydrochloric acid → sodium chloride + water

Question 57

Give the word equation for the reaction between potassium hydroxide and nitric acid

Answer 57

potassium hydroxide + nitric acid → potassium nitrate + water

Question 58

What is the name for a reaction where the pH moves towards 7.

Answer 58

Neutralisation

Question 59

What colour of universal indicator is usually associated with acidic substances.

Answer 59

Red

Question 60

What colour of universal indicator is usually associated with alkaline substances.

Answer 60

Purple / Blue

Question 61

What colour of universal indicator is usually associated with neutral substances.

Answer 61

Green