Quantitative Chemistry Definitions

Question 1

What is a relative mass?

Answer 1

A comparative value (modern compare to an atom of Carbon-12)

Question 2

Definition of relative atomic mass?

Answer 2

The average mass of an atom of an element of a scale where an atom of Carbon- 12 is exactly 12

Question 3

Definition of relative molecular mass

Answer 3

The average mass of an element/ compound on a scale where an atom of Carbon-12 is exactly 2 (used with molecules of a element/ compound)

Question 4

Definition of relative formula mass

Answer 4

The average mass of a formula unit of a scale where an atom of Carbon-12 is exactly 12 (used with ionic/ giant covalent compounds)

Question 5

How many particles does 1 mole of a substance have in?

Answer 5

6.02 x 10^23 particles (avogadros number)

Question 6

What is the empirical formula?

Answer 6

The simplest ratio of atoms in each element in a compound

Question 7

What is the molecular formula?

Answer 7

The actual numbers of atoms of each element in a molecule

Question 8

Does a molecular formula apply to ionic compounds?

Answer 8

No

Question 9

Reading (e.g reading from some apparatus) definition

Answer 9

A value found from a single judgement when using a piece of equipment

Question 10

What is the definition of a measurement?

Answer 10

A value found from the differences between the judgement of two readings

Question 11

What is a cation?

Answer 11

A positive (metal) ion

Question 12

What is an anion?

Answer 12

A negative (non-metal) ion

Question 13

What are ions?

Answer 13

Charged particles formed when atoms lose or gain electrons

Question 14

What are three substances that contain ions?

Answer 14

Ionic metal-non metal compounds
Ammonium salts
Acids in an aqueous solution

Question 15

What is a soluble salt?

Answer 15

One which will dissolve in water at room temperature

Question 16

What is an insoluble salt?

Answer 16

One which will not dissolve in water at room temperature

Question 17

What is a sparingly soluble salt?

Answer 17

One which will dissolve slightly in water.

Question 18

What is a limiting reagent?

Answer 18

A reactant that is not in excess (less moles)

Question 19

What are three reasons why the actual yield from a reaction will be less than the theoretical yield?

Answer 19

• Chemicals can be lost during transfer between containers
• The reaction may be reversible, so not all starting materials may fully react
• There could be other products formed in side reactions.

Question 20

Atom economy definition

Answer 20

A measure of what proportion of the products are the desired product and how much is waste

Question 21

Do chemical processes with high atom economies produce more or less waste that ones with a lower atom economy?

Answer 21

Less waste

Question 22

What are two assumptions that we make when we say a gas is ideal?

Answer 22

There are no forces of attraction between the particles and the size of the particles is negligible.

Question 23

What does the concentration of a solution tell us?

Answer 23

It tells us how much solute is dissolved in a know volume of a solution.

Question 24

What is a titration?

Answer 24

A procedure where a solution of known concentration is used to determine an unknown concentration

Question 25

What are concordant results?

Answer 25

Results withing plus or minus 0.10 cm3

Question 26

What do you have to assume about the reagents to do with safety in a titration?

Answer 26

You assume all reagents and liquids are toxic, corrosive and flammable

Question 27

Definition of a standard solution

Answer 27

It is a solution whose concentration is known precisely

Question 28

What type of indicator is used in a titraition and what colour does it turn at the end point?

Answer 28

Phenolphthalein, turns colourless

Question 29

What can we do to improve the accuracy in a titration?

Answer 29

Washing splashed down the sides of the conical flask with distilled water near the end point, this improved the accuracy as it makes sure that all the acid has reacted with the alkali so the reaction is complete (no acid on the sides of the flask)

Question 30

How does the calculated concentration change if the pipette is only washed with water before the titration?

Answer 30

The concentration would be inaccurate and higher than the actual value as the concentration of NaOH would be more dilute, so less acid would be needed, so the value for the volume of acid needed would be lower.

Question 31

How would the burette only being rinsed with water before the titration affect the calculated concentration of the acid?

Answer 31

The calculated concentration would be lower as the concentration of acid in the burette would be lower so more would be needed to neutralise the alkali.

Question 32

How would we reduce the percentage uncertainty in titrations (using the biggest source of uncertainty)?

Answer 32

The largest source of uncertainty is the burette, so we would increase the volume of alkali used so that we would need more acid to neutralise it.

Question 33

What does a back titration involve?

Answer 33

It involves reacting a know mass of an insoluble solid with a known excess of acid/ alkali, so only some of the acid/ alkali will react with the solid and some will remain left over. The excess acid/ alkali can then be made up into a solution and titrated to determine how much remains.

Question 34

What does a chemical equation tell us?

Answer 34

What is happening in a reaction

Question 35

What non-metallic elements exist as diatomic molecules?

Answer 35

Have No Fear Of Ice Cold Beer Hydrogen Nitrogen Fluorine Oxygen Iodine Chlorine Bromine Astatine