C2.3 - Atomic Structure, Analysis, and Quantitative Chemistry

Question 1

What is the “mass number”?

Answer 1

Protons + neutrons

Question 2

What is the “atomic number”?

Answer 2

Number of protons and the number of electrons

Question 3

Why do stable atoms have no charge?

Answer 3

In a stable atom, the number of positive protons is equal to the number of negative electrons, hence the charges cancel out and the atom has no overall charge.

Question 4

Which sub-atomic particle do atoms of the same element have the same?

Answer 4

Atoms of the same element all have the same number of protons.

Question 5

What are the masses of a proton, neutron, and electron?

Answer 5

Proton - 1

Neutron - 1

Electron - Very small - 1/200 of a proton

Question 6

What is an isotope?

Answer 6

Isotopes are different atomic forms of the same element.

They have the same number of protons but a different number of neutrons.

Question 7

Isotopes have the same what?

Answer 7

Isotopes must have the same atomic number but different mass numbers.

Question 8

What is the relative atomic mass?

Answer 8

The relative atomic mass is a means of comparing the mass of an atom of the element in question compared with a carbon-12 isotope.

Question 9

What is the way of finding the relative atomic mass?

Answer 9

The atomic mass is the mass number or “top number”.

Question 10

What is the relative atomic mass an average of?

Answer 10

The relative atomic mass is an average of all of the different isotopes of an element.

Question 11

What is the relative formula mass?

Answer 11

The relative formula mass, Mr, is simply the relative atomic masses added together.

Question 12

What is meant by a mole?

Answer 12

One mole of a substance is its relative formula mass in grams.

Question 13

What is the formula for finding the mole amount?

Answer 13

Number of moles = Mass of element in grams/Mr of element

Question 14

What is the percentage by mass formula?

Answer 14

Ar * Number of Atoms/Mr (x100)

Question 15

What is the purpose of the “x100” in the percentage by mass formula?

Answer 15

The “x100” is to turn the answer into a percentage.

Question 16

What is the empirical formula?

Answer 16

The empirical formula is the simplest whole number ratio of elements in a compound.

Question 17

What is the method for the empirical formula?

Answer 17

Take the mass/percentage and divide it by the mass number.

Get the number of moles and divide this by the smallest value there.

Turn this into a whole number if needs be.

Question 18

What happens if the answers to an empirical formula question are decimals?

Answer 18

If the answer is a decimal, make it into a positive, alongside the other number too.

Question 19

What is the method for a reacting masses question?

Answer 19

Writing out a balanced equation means you can calculate the masses of the reactants and products.

Work out the Mr of the required chemicals.

Divide the Mr by the amount given and then use that in a division of the product.

Question 20

What is meant by the yield?

Answer 20

The amount of product in a chemical reaction is called the yield.

Question 21

What is the effect of more reactants on the yield?

Answer 21

The more reactants you start with, the higher the yield.

The percentage yield does not depend on this.

Question 22

What is the formula for percentage yield?

Answer 22

Percentage yield = actual yield (g)/predicted yield (g) (x100)

Question 23

What is the produced yield also known as?

Answer 23

The percentage yield is also called the theoretical yield.

Question 24

What is an 100% yield?

Answer 24

A 100% yield means you got all of the expected product.

Question 25

What is a 0% yield?

Answer 25

A 0% yield means that no reactant was converted to product.

Question 26

Why are yields less than 100%?

Answer 26

Even though no atoms are gained or lost in reactions, the percentage yield is never 100% because:

The reaction is reversible.

Some of the product may be lost when you filter a liquid to remove solid particles.

Side reactions may be occurring.

Question 27

Why does a reaction being reversible mean the yield is never 100%?

Answer 27

The reaction being reversible means some of the products are always reacting together to change back to the original reactants. This will mean a lower yield.

Question 28

What is sustainable development in terms of yield?

Answer 28

Sustainable development is about ensuring we do not use resources faster than they can be replaced. Using as little energy as possible to create the highest product yield possible means that resources are saved.

Question 29

What are food additives?

Answer 29

Substances added to food to improve its qualities are called food additives.

Question 30

What types of food additives are there?

Answer 30

Food additives may be natural products and synthetic products.

Question 31

What can chemical analysis do?

Answer 31

Chemical analysis can check food to ensure only safe, permitted food additives have been used.

The methods used include paper chromatography and using a mass spectrometer.

Question 32

Outline paper chromatography.

Answer 32

Paper chromatography can involve putting a colour onto paper and allowing a solvent (ethanol, water, etc) to move up the substance.

Question 33

Why is a pencil line used in paper chromatography?

Answer 33

The pencil line used is to ensure the line doesn’t dissolve in the solvent like pen would.

Question 34

What is the purpose of a lid in paper chromatography?

Answer 34

A lid at the top prevents evaporation.

Question 35

Why do colours move different distances in paper chromatography?

Answer 35

The colours move different distances depending on their solubility.

Question 36

What qualities do instrumental methods possess?

Answer 36

Instrumental analysis are sensitive (only small amounts needed), fast, and accurate.

Computers can process the results quickly.

Question 37

What are the downsides of instrumental methods?

Answer 37

The equipment is very expensive and special training is needed to use it.

Question 38

Outline the process of gas chromatography.

Answer 38

A gas is used to carry substances through a column packed with solid material.

The samples are vaporised.

Question 39

What is the “retention time”?

Answer 39

The substances in gas chromatography travel through the column at different speeds, so they separate out and the amount of time spent in the column is its retention time.

Question 40

What is the purpose of a gas chromatograph?

Answer 40

A gas chromatograph can show the number of peaks and ergo the number of different compounds in something.

Question 41

What does a mass spectrometer do?

Answer 41

A mass spectrometer can identify the substances very accurately by giving the relative molecular mass by looking at the molecular ion peak.