C2.3

Question 1

How do you work out the number of neutrons?

Answer 1

Mass number - atomic number

Question 2

What actually is the atomic mass?

Answer 2

An average mass number of the isotopes

Question 3

Why does chlorine have a relative atomic mass (Ar) or 35.5?

Answer 3

~ Because it is an average mass number of the isotopes

~ It does NOT mean that it has half a proton or neutron

Question 4

What is the relative formula mass (Mr) of H2O?

Answer 4

1 x 2 + 16

2 + 16 = 18

Question 5

The relative atomic mass (Ar) is the mass of what?

Answer 5

A particular atom compared to the 12C isotope

Question 6

How do you work out the percentage by mass of an element in a compound?

Answer 6

Relative formula mass of the compound

Question 7

What is the empirical formula?

Answer 7

The simplest whole number ratio of atoms of each element in a compound

Question 8

What is the mass of a proton?

Answer 8

1

Question 9

What is the mass of a neutron?

Answer 9

1

Question 10

What is the mass of an electron?

Answer 10

Very small

Question 11

What is the mass number made up of?

Answer 11

Protons + neutrons

Question 12

What is one mole of a element?

Answer 12

The relative atomic mass in grams

Question 13

How can elements and compounds be detected?

Answer 13

Using instrumental methods as they’re accurate, sensitive, rapid and are useful when the sample is very small

Question 14

What can chemical analysis be used to identify?

Answer 14

Additives in food

Question 15

How can artificial colours be detected and identified?

Answer 15

Paper chromatography

Question 16

What does gas chromatography do?

Answer 16

Allows the separation of a mixture of compounds

Question 17

Why may the mass of a product change in a reaction?

Answer 17

~ The reaction may not go to completion as it’s reversible
~ Some of the product may be lost when it’s separated from the reaction mixture
~ Some of the reactants may react in ways different from the expected reaction

Question 18

What is the yield?

Answer 18

The amount of a product obtained

Question 19

What is an example of a reversible reaction?

Answer 19

Ammonium chloride ~ ammonia + hydrogen chloride

Question 20

What is the retention time?

Answer 20

The time taken for a substance to travel through the column

Question 21

What is used as the solvent in paper chromatography?

Answer 21

Water or ethanol

Question 22

What do the ink spots (solute) tell you?

Answer 22

How many chemicals are in the substance

Question 23

Why is the baseline on paper chromatography marked with a pencil?

Answer 23

So it doesn’t run up with the ink and dissolve in the solvent

Question 24

What are some reasons why gas chromatography is better than paper chromatography?

Answer 24

More accurate, sensitive and rapid

Question 25

What does the filter paper do in paper chromatography?

Answer 25

Detects the chemicals and gives a reading of how many chemicals there are

Question 26

What is the process of paper chromatography?

Answer 26

~ Pencil line put on filter paper ~ Spots of samples are put on the line ~ Put into a beaker of solvent ensuring that the sample is not put in the solvent ~ Lid is put on beaker to prevent evaporation ~ Wait for solvent to soak up paper, dissolve samples and separate them out

Question 27

Why do the different samples separate out?

Answer 27

~ Some dissolve really easily in the solvent and move up quickly ~ Some don't dissolve as well and move up slowly

Question 28

How does gas chromatography work?

Answer 28

~ Sample is vaporised and passed through a column ~ The chemicals are carried through the column at different speeds and they separate ~ A detector detects the different chemicals and shows them as a peak on a chart

Question 29

What does the molecular ion peak give you?

Answer 29

The relative formula mass of the compound

Question 30

Why is a mass spectrometer useful?

Answer 30

It can identify chemicals quickly, accurately and can detect small amounts

Question 31

What do the number of peaks show on the output data from gas chromatography?

Answer 31

The number of different compounds

Question 32

Where is the molecular ion peak found?

Answer 32

The peak on a mass spectrometer which is furthest on the right

Question 33

What is one mole of a compound?

Answer 33

The relative formula mass in grams

Question 34

A compound contains 1 mole of carbon, 2 moles of hydrogen and 1 mole of oxygen. What is the empirical formula?

Answer 34

CH2O

Question 35

Why may the percentage yield after a reaction be lower than expected?

Answer 35

~ Some product may be lost when separated from the reaction mixture ~ Reaction might be reversible ~ Reactants may react in ways which are different to what is expected

Question 36

How do you work out the % yield?

Answer 36

Amount produced -------------------- X 100 Maximum amount possible

Question 37

What are solvents used for?

Answer 37

Dissolving substances that can't dissolve in water