Moles 1 + 2 key notes

Question 1

how to calculate mass

Answer 1

mass = Mr x moles

Question 2

how to work out number of particles

Answer 2

number of particles = moles x avogardros constant

Question 3

what empirical formula

Answer 3

simplest ratio of atoms of each element in a compound

Question 4

molecular formula

Answer 4

actual number of atoms in each element

Question 5

how to work out molecular formula

Answer 5

mr/ mass of empirical formula

Question 6

how to work out moles

Answer 6

% mass/ ar

Question 7

method for heating a crucible

Answer 7

1. weigh an empty clean dry crucible and lid
2. add 2g of hydrated calcium sulphate to the crucible and weigh again
3. heat strongly with a bunsen burner for a couple of minutes
4. allow to cool
5. weigh crucible again and contents
6. hea crucible and reweigh until a constant mass

Question 8

why does the crucible need to be dry

Answer 8

a wet crucible woul give an inaccurate result

causes mass lost to be too large as water would be lost when heating

Question 9

why use a lid when heating a crucible

Answer 9

lid improves accuracy of the experiment as it prevents loss of solid from crucible

it should be loose fitting to allow gas to escape

Question 10

how could eating a crucible procedure be improved

Answer 10

heat to a constant mass

so all water evaporates

heat longer or use a smaller mass

Question 11

ideal gas equation

Answer 11

pV= nRT

pressure (pa)
KPa to Pa = x1000
volume (m3)
R= 8.31 J K-1 mol-1
Temperat

Question 12

% mass economy

Answer 12

mass of desired product/ total mass of all reactants
x 100

Question 13

% yield

Answer 13

actual yield/theoretical yield x 100

mass/ theo mass
moles/ theo moles

Question 14

density

Answer 14

mass / volume

Question 15

concentration

Answer 15

moles/ volume

conc = mol/dm-3