C2.3 Atomic structure, analysis and quantitative chemistry

Question 1

What is the relative mass of a neutron?

Answer 1

1

Question 2

What is the relative mass of an electron?

Answer 2

very small

Question 3

What is the mass number of an atom?

Answer 3

The total number of protons and neutrons

Question 4

What is an isotope?

Answer 4

Atoms of the same element that have a different number of neutrons.

Question 5

What does the relative atomic mass of an element compare the mass of atoms with?

Answer 5

with the carbon 12 isotope

Question 6

What is the relative formula mass of a compound?

Answer 6

the sum of the relative atomic masses in a compound

Question 7

What is the relative mass of a proton?

Answer 7

1

Question 8

What is one mole of a substance?

Answer 8

The relative formula mass of a substance in grams

Question 9

How do you find the number of moles of a substance?

Answer 9

number of moles= mass (g) divided by relative formula mass

moles, mass, ram

Question 10

How can elements and compounds be detected and identified by?

Answer 10

using instrumental methods

Question 11

What are some advantages of using instrumental methods to detect and identify elements and compounds?

Answer 11

• accurate
• sensitive
• rapid
• useful when the sample is very small

Question 12

Describe paper chromatography

Answer 12

can be used to identify additives and colourings in foods.

extract colour from food by placing it on a pencil baseline on filter paper in a beaker with solvent

keep the baseline above the level of solvent.

the solvent will seep up the paper, taking dyes with it. Different dyes form spots at different places.

Question 13

In paper chromatography, why do we use pencil to draw a base line not pen?

Answer 13

pen will dissolve in the solvent and confuse the experiment

Question 14

In paper chromatography, why might you put a lid on the beaker?

Answer 14

to prevent evaporation of solvent

Question 15

What does GC-MS stand for?

Answer 15

gas chromatography linked to mass spectroscopy

Question 16

Describe how a GC-MS works

Answer 16

• different substances, carried by a gas, travel through a column packed with solid material, at different speeds so that they become separated.
• The number of peaks on the output of a gas chromatograph shows the number of compounds present.
• the position of the peaks on the output indicates the retention time
• the output from the gas chromatography column can be linked to a mass spectrometer, which can be used to identify the substances leaving the end of the column
• the mass spectrometer can identify substances very quickly and accurately and can detect very small quantities. It also gives the relative molecular mass of each substance separated in the column.

Question 17

in GC-MS, what shows the number of compounds present?

Answer 17

the number of peaks on the output of a gas chromatograph

Question 18

in GC-MS, what indicates the retention time?

Answer 18

the position of the peaks on the gas chromatograph

Question 19

In GC-MS, how can you tell the molecular mass?

Answer 19

by reading off the molecular ion peak

Question 20

In GC-MS, what is the retention time?

Answer 20

the time taken for a substance to travel through the column

Question 21

How can you work out the percentage of an element in a compound?

Answer 21

% of element = relative mass of element divided by relative formula mass of compound

x100

Question 22

What is a reversible reaction?

Answer 22

a reaction where the products of the reaction can themselves react to produce the original reactants.

Question 23

Why is it not always possible to obtain the calculated amount of product? (3 reasons)

Answer 23

• The reaction may not go to completion because it is reversible
• some of the product may be lost when it is separated from the reaction mixture
• Some of the reactants may react in ways different from expected

Question 24

The amount of product obtained from a reaction is know as…

Answer 24

the yield

Question 25

What is a definition of percentage yield.

Answer 25

when the amount of product obtained from a reaction is compared with the maximum theoretical amount

Question 26

How do you calculate percentage yield?

Answer 26

percentage yield= actual yield divided by predicted yield x 100

Question 27

Give an example of a reversible reaction

Answer 27

ammonium chloride = ammonia + hydrogen chloride

Question 28

in terms of yield, how can we make sure resources are saved?

Answer 28

by using as little energy as possible to create the highest product yield possible

Question 29

What is it an advantage if a reaction has a high atom economy?

Answer 29

less waste

less pollution

better for sustainable development

Question 30

In GC-MC, in which part is the mixture separated?

Answer 30

in the column

Question 31

In a GC-MS, in which part is the relative molecular mass of each of the compounds in the mixture measured?

Answer 31

in the mass spectrometer

Question 32

Describe how gas chromatography can separate substances in a mixture of compounds

Answer 32

Substances are carried by a gas

through a column

at different speeds

Question 33

In GC-MS, what information does the molecular ion peak give about the molecule?

Answer 33

The relative molecular mass

Question 34

What are some advantages of gas chromatography compared with paper chromatography?

Answer 34

rapid

accurate

sensitive

Question 35

What does gas chromatography do to a mixture?

Answer 35

separates

Question 36

What information does mass spectroscopy give?

Answer 36

identifies substances by finding out the relative molecular mass of each substance

Question 37

Why do compounds separate in a gas chromatography column?

Answer 37

different substances travel at different speeds

they have different retention times