Chemistry, unsure topics

Question 1

What is the formula to calculate the number of moles?

Answer 1

moles = mass (g) ÷ relative formula mass (Mr)

Question 2

How do you calculate the mass using moles?

Answer 2

mass = moles × Mr

Question 3

How can you find the Mr of a compound?

Answer 3

Add up the relative atomic masses (Ar) of all atoms in the formula

Question 4

How do you calculate the empirical formula from mass or % composition?

Answer 4

1. Divide each element’s mass by its Ar
2. Divide by the smallest value
3. Multiply to get whole numbers

Question 5

What is the empirical formula of a compound with 24g C and 8g H?

Answer 5

C: 24/12 = 2, H: 8/1 = 8 → divide by 2 → CH₄

Question 6

What is simple distillation used for?

Answer 6

Separating a liquid from a solution (e.g. pure water from salt water)

Question 7

How do you carry out simple distillation?

Answer 7

Heat the solution → liquid evaporates → cools in condenser → collects as distillate

Question 8

What is fractional distillation used for in chemistry?

Answer 8

Separating a mixture of liquids with different boiling points

Question 9

What is chromatography used for?

Answer 9

Separating and identifying substances in a mixture

Question 10

How do you carry out a chromatography experiment?

Answer 10

1. Draw pencil line on filter paper
2. Add spots of ink
3. Dip bottom into solvent
4. Solvent carries dyes up

Question 11

How do you calculate the Rf value in chromatography?

Answer 11

Rf = distance moved by substance ÷ distance moved by solvent

Question 12

What are the main stages of water treatment in the UK?

Answer 12

1. Screening 2. Sedimentation 3. Filtration 4. Chlorination

Question 13

How is water treated to make it potable?

Answer 13

Filtered to remove solids, then sterilised with chlorine, ozone or UV

Question 14

What is the difference between strong and weak acids?

Answer 14

Strong acids fully ionise in water; weak acids only partially ionise

Question 15

Give an example of a strong acid

Answer 15

Hydrochloric acid (HCl)

Question 16

Give an example of a weak acid

Answer 16

Ethanoic acid (CH₃COOH)

Question 17

How does the pH scale relate to acid strength?

Answer 17

Lower pH = higher concentration of H⁺ ions

Question 18

What is the general word equation for acid + metal?

Answer 18

Acid + Metal → Salt + Hydrogen

Question 19

What is the general word equation for acid + base?

Answer 19

Acid + Base → Salt + Water

Question 20

What is the general word equation for acid + carbonate?

Answer 20

Acid + Carbonate → Salt + Water + Carbon dioxide

Question 21

How does fractional distillation of crude oil work?

Answer 21

Crude oil is heated → enters column → fractions condense at different heights based on boiling points

Question 22

What is a monomer?

Answer 22

A small molecule that can join with others to form a polymer

Question 23

What is addition polymerisation?

Answer 23

Monomers with double bonds join to form a long chain with no small molecules released

Question 24

What is the repeating unit in addition polymers?

Answer 24

The monomer without the double bond, in brackets with n outside

Question 25

What is condensation polymerisation?

Answer 25

Monomers join and release a small molecule (usually water)

Question 26

What molecules are usually released in condensation polymerisation?

Answer 26

Water or HCl

Question 27

Why is polymer disposal a problem?

Answer 27

Most polymers are non-biodegradable and cause environmental pollution

Question 28

Name two ways of disposing of polymers

Answer 28

Landfill and incineration (burning)

Question 29

What is a benefit and a drawback of incinerating polymers?

Answer 29

Benefit: energy released; Drawback: toxic gases may be produced

Question 30

Why is cracking necessary?

Answer 30

To break long hydrocarbons into shorter, more useful ones

Question 31

What are the products of cracking?

Answer 31

Alkanes and alkenes

Question 32

What are two types of cracking?

Answer 32

Thermal cracking and catalytic cracking

Question 33

Describe how catalytic cracking is done

Answer 33

Heat hydrocarbons → vaporise → pass over hot catalyst (e.g. zeolite)

Question 34

What colour does lithium produce in a flame test?

Answer 34

Crimson red

Question 35

What colour does sodium produce in a flame test?

Answer 35

Yellow/orange

Question 36

What colour does potassium produce in a flame test?

Answer 36

Lilac

Question 37

What colour does calcium produce in a flame test?

Answer 37

Brick red

Question 38

What colour does copper produce in a flame test?

Answer 38

Green

Question 39

What is flame photometry used for?

Answer 39

To identify metal ions and determine their concentration

Question 40

How does flame photometry work?

Answer 40

Each metal ion gives a unique emission spectrum

Question 41

Why is flame photometry more accurate than flame tests?

Answer 41

It is quantitative and can detect mixtures

Question 42

What is a nanoparticle?

Answer 42

A particle 1–100 nm in size

Question 43

Why are nanoparticles useful?

Answer 43

Large surface area to volume ratio gives them special properties

Question 44

Give two uses of nanoparticles

Answer 44

Sun creams and medicine delivery systems

Question 45

What is a potential risk of nanoparticles?

Answer 45

Unknown effects on human health and the environment