Module 2 - Amount of Substance

Question 1

define relative atomic mass

Answer 1

weighted mean mass of an atom relative to 1/12th of the mass of one atom of carbon 12

Question 2

define relative formula mass

Answer 2

term used when working out the calculation for compounds with giant structures

Question 3

examples of giant structures for relative formula mass

Answer 3

giant ionic, giant covalent, giant metallic

Question 4

define relative molecular mass

Answer 4

term used when working out the calculation for compounds that are simple molecules

Question 5

equation for percentage of an element

Answer 5

number of atoms of element x relative atomic mass of element / relative formula mass of compound x100

Question 6

define molar mass

Answer 6

the mass per mol of a substance in g mol^-1

Question 7

what does the mass of one mole equal

Answer 7

the ar of that substance

Question 8

define amount of substance

Answer 8

chemists use amount of substance as a means of counting the number of particles in a substance. its unit is the mole (mol)

Question 9

define avogadros constant

Answer 9

6.02 x 10^23. the number of atoms per mole of carbon 12

Question 10

equation for number of atoms/ions/molecules

Answer 10

moles x 6.02x10^23

Question 11

equation for number of mols

Answer 11

mass (g) / molar mass

Question 12

units for molar mass

Answer 12

g mol -1

Question 13

define molecular formula

Answer 13

the number and type of atoms in each element of a molecule

Question 14

define empirical formula

Answer 14

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

Question 15

steps to calculate empirical formula

Answer 15

• calculate number of moles
• divide number of moles by smallest value for a ratio
• adjust to make ratios whole numbers

Question 16

define water of crystallisation

Answer 16

water molecules that are bonded into a crystalline structure of a compound

Question 17

what does heated hydrated copper sulfate form

Answer 17

anhydrous copper sulfate + water

Question 18

symbol equation for heating copper sulfate

Answer 18

CuSO4 . 5H2O -> CuSO4 + 5H2O

Question 19

define hydrated

Answer 19

a crystallised compound containing water molecules

Question 20

define anhydrous

Answer 20

contains no waters of crystallisation

Question 21

method for calculating amount of water

Answer 21

-weigh the crucible
-add a known amount of hydrated salt
-weigh the crucible and hydrated salt together
-heat the hydrated salt strongly for a few minutes
-weigh and heat the sample until the mass stays constant

Question 22

assumptions in calculating amount of water

Answer 22

-assuming all water has been lost by heating to constant mass
-when heating the salt its not breaking down further to other compounds

Question 23

define molar gas volume

Answer 23

the volume per mole of gas molecules at the stated temperature and pressure (RTP)

Question 24

room temperature

Answer 24

25 degrees

Question 25

room pressure

Answer 25

101 kPa

Question 26

what is the volume of a gas at RTP

Answer 26

1 mole of gas is 24.0dm^3

Question 27

equation for volume of a gas in dm^3

Answer 27

moles = volume (dm3) / 24

Question 28

equation for volume of a gas in cm^3

Answer 28

moles = volume (cm3) / 24,000

Question 29

ideal gas equation

Answer 29

pV = nRT

Question 30

degrees to kelvin conversion

Answer 30

add 273

Question 31

kPa to Pa

Answer 31

add x10^3 on the end

Question 32

cm^3 to m^3

Answer 32

add x10^-6 on the end

Question 33

dm^3 to m^3

Answer 33

add x10^-3 on the end

Question 34

ideal gas equation in words

Answer 34

volume x pressure = amount of gas x ideal gas constant x temperature

Question 35

volume units in ideal gas equation

Answer 35

m^3

Question 36

pressure units in ideal gas equation

Answer 36

Pa

Question 37

amount of gas units in ideal gas equation

Answer 37

mol

Question 38

temperature units in ideal gas equation

Answer 38

K

Question 39

define stoichiometry

Answer 39

-the ratio, of the amount in moles, of each substance in a chemical reaction

Question 40

steps for stoichiometry calculation

Answer 40

-write mr of substance known and unknown -calculate moles of known -ratio for moles of unknown -work out question

Question 41

steps for limiting reactant calculation

Answer 41

-calculate moles for both reactants -do a ratio of how much you need for each one -use the limiting reactant moles to work out the rest of the question

Question 42

units for concentration

Answer 42

mol dm^-3

Question 43

equation for number of moles (concentration)

Answer 43

volume x concentration / 1000

Question 44

units of volume in concentration equation

Answer 44

cm^3

Question 45

why do you divide by 1000 in the concentration equation

Answer 45

to convert volume to dm^3

Question 46

what is percentage yield

Answer 46

the amount of product made from the starting materials

Question 47

why does no reaction ever have 100% yield

Answer 47

-the reaction may have not gone to completion -side reactions may have occurred -purification of the product may have resulted in loss of product

Question 48

percentage yield equation

Answer 48

actual moles/ theoretical moles x 100

Question 49

percentage yield calculation steps

Answer 49

-workout mr or the reactant and product you have a mass for -work out the actual moles (mass of the product) -workout the theoretical moles (mass of the reactant-> ratio) -put in equation

Question 50

what happens in an ideal reaction

Answer 50

-all reactant atoms end up within the useful product molecule -no waste is produced

Question 51

which reactions have low atom economy

Answer 51

-inefficient, wasteful reactions

Question 52

which reactions have high atom economy

Answer 52

-efficient processes have high atom economy

Question 53

why are high atom economy reactions important

Answer 53

-sustainable development -conserve natural resources -create less waste

Question 54

atom economy equation

Answer 54

sum of molar masses of all desired products / sum of molar masses of all products x100

Question 55

what is atom economy a measure of

Answer 55

-the proportion of reactant included in the final useful product

Question 56

how are atom economy and percentage yield linked in a reaction

Answer 56

a reaction can have a -high percentage yield -low atom economy

Question 57

what is the percentage atom economy if a reaction has 1 product

Answer 57

100%

Question 58

define mole

Answer 58

the amount of any substance containing as many particles as there are carbon atoms in 12g of carbon 12 (6.02x10^23 particles)

Question 59

which reactant do you use for theoretical moles in percentage yield if there are multiple

Answer 59

the limiting reactant