5. formula, equations and amounts of substance

Question 1

what is the mole

Answer 1

unit of measurement for substances

Question 2

what is avogadros constant

Answer 2

6.022x10^23

Question 3

what is relative atomic mass

Answer 3

the mean mass of an element relative to 1/12th of the mass of an atom of carbon-12

Question 4

what is relative molecular mass

Answer 4

the mean mass of a molecule of a compound relative to 1/12th of the mass of an atom of carbon-12

Question 5

what is empirical formula

Answer 5

the simplest whole number ration of atoms of each element in a compound

Question 6

what is molecular formula

Answer 6

the actual number of each atom in the molecule.

Question 7

how to work out the multiplier to scale up the empirical formula

Answer 7

true Mr/empirical Mr

Question 8

what is the ideal gas equation

Answer 8

pV = nRT = mRT/Mr
p = pressure
v = volume
n = moles
R = 8.31 ideal gas constant
T = temperature in Kelvin
m = mass

Question 9

what is percentage yield

Answer 9

how much of the maximum amount of product you obtained during an experiment.

Question 10

equation for percentage yield

Answer 10

(experimental mass/ theoretical mass) x 100

Question 11

what is atom economy

Answer 11

a measure of efficiency as it measures the proportion of reactant that is converted into the desired product

Question 12

equation for atom economy

Answer 12

(Mr desired product / sum or Mr reactants) x 100

Question 13

what is a titration

Answer 13

a practical method where a standard solution of a known concentration is reacted with an unknown concentration in order to determine its concentration.

Question 14

how to create a standard solution

Answer 14

1. weigh solid in boat
2. weigh boat
3. record different in mass
4. add water and stir glass until dissolved
5. transfer to volumetric flask
6. make up to 250 cm mark with distilled water
7. shake flask

Question 15

errors that can occur when making a standard solution

Answer 15

systematic errors on the balance
lost substance in the transfer process
overfilling of volumetric flask

Question 16

how to reduce errors when making a standard solution

Answer 16

washing methods and reading volumes from the bottom of the meniscus

Question 17

how to complete a titration

Answer 17

1. fill the burette with standard solution of known concentration
2. use pipette filler and pipette to transfer 25cm3 of the solution with unknown concentration into a conical flask
3. add a few drops of indicator
4. record the initial burette reading
5. titrate the contents until a permanent colour change can be seen
6. record final burette reading and calculate titre volume
7. repeat until 2 concordant results within 0.1 cm of each other

Question 18

how to measure percentage uncertainty

Answer 18

uncertainty / measurement x 100