Chapter 3 - Amount of Substance (MODULE 2)

Question 1

What is avogadro’s constant

Answer 1

6.02 x 10^23

Question 2

What is 6.02x10^23 molecules of a substance known as

Answer 2

a mole

Question 3

How can one mole of a substance easily be calculated

Answer 3

relative atomic mass in grams

Question 4

What is molar mass
- what are the units

Answer 4

mass in grams of a mole of a substance
- g/mol

Question 5

What equation links mass, molar mass and number of moles

Answer 5

moles = mass / Mr

Question 6

What is the molecular formula

Answer 6

number of atoms of each element in a compound

Question 7

What is the empirical formula

Answer 7

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

Question 8

What is the relative molecular mass

Answer 8

comparison of the mass of a molecule with the mass of 1/12 of carbon 12

Question 9

What is the relative formula mass

Answer 9

compares the mass of a formula unit with the mass of carbon-12

Question 10

what does it mean for a crystal to be hydrated
- what is this known as

Answer 10

water molecules are a part of their crystalline structure
- water of crystallisation

Question 11

how can water of crystallization be removed

Answer 11

heating to evaporate until mass is constant

Question 12

How is water of crystallization indicated on a compound

Answer 12

large dot between compound and water units

Question 13

What are two assumptions made when when heating hydrated compounds to make anhydrous compounds

Answer 13

1. all water has been lost
2. no further decomposition of salts / crystals

Question 14

how many cm3 is a litre and millilitre

Answer 14

litre: 1000cm3 / 1dm3
millilitre : 1cm3

Question 15

What is the equation linking moles, concentration and volume

Answer 15

moles = concentration x volume

Question 16

What is a standard solution

Answer 16

a solution of known concentration

Question 17

How are standard solutions made

Answer 17

dissolve an exact mass of solute in a solvent and make up the solution to an exact volume

Question 18

What is the equation linking molar concentration and mass concentration

Answer 18

mass concentration = molar concentration x Mr

Question 19

what is the molar gas volume

Answer 19

volume per mole of gas at a stated temperature and pressure

Question 20

What is RTP approximately valued at

Answer 20

20 degrees C and 101kPa (1 atm)

Question 21

What is the volume of 1 mol of gas at RTP
- What is the molar gas volume at RTP

Answer 21

24 dm3
- 24 dm3 / mol

Question 22

What are the four assumptions made for the molecules making up an ideal gas

Answer 22

• random motion
• elastic collisions
• negligible size
• no intermolecular forces

Question 23

what is the ideal gas equation

Answer 23

pV = nRT

pressure x volume = moles x ideal gas constant x temperature

Question 24

What are the units used in the ideal gas equation

Answer 24

pressure - Pa
Volume - m^3
Temperature : Kelvin

Question 25

What is the ideal gas constant

Answer 25

8.31 J/ (mol K)

Question 26

How to convert from: cm^3 to m^3 cm^3 to dm^3 dm^3 to m^3 celsius to kelvin Pascals to KiloPascals

Answer 26

x 10^-6 x 10^-3 x 10^ -3 + 273 x 10^-3

Question 27

What is the stoichiometry of a reaction

Answer 27

the ratio of moles of each substance in a reaction

Question 28

What are two reasons balanced equations are used

Answer 28

- to work out how much reactant is needed to prepare a certain amount of product - quantities of products that should be prepared from a certain amount of reactant

Question 29

What is percentage yield (not the equation)

Answer 29

the actual yield of a reaction compared to the theoretical yield

Question 30

What is the equation for percentage yield

Answer 30

(actual yield / theoretical yield ) x 100

Question 31

What are three reasons as to why the percentage yield may not be 100%

Answer 31

- reaction may not have gone to completion - other reactions may have taken place alongside the main reaction - purification of the product may have led to loss in some product

Question 32

What is the limiting reagent

Answer 32

the reactant that is not in excess - all is used up and limits more reaction from happening

Question 33

What is atom economy

Answer 33

a measure of how well atoms have been utilised

Question 34

What is the equation for atom economy

Answer 34

sum of molar mass of desired products / sum of molar mass of all products x 100

Question 35

Why is a high atom economy desirable

Answer 35

less waste and makes the best use of natural resources

Question 36

what factors other than atom economy affect sustainability of a reaction

Answer 36

- availability of resources - percentage yield