physical chem; amount of substance

Question 1

define the term relative atomic mass

Answer 1

it’s the average mass of 1 atom compared to 1/12th of the mass of 1 atom of carbon-12

Question 2

what is avogadro’s number?

Answer 2

6.022 × 10²³

Question 3

how can we calculate no.of particles in a substance

Answer 3

no.of particles = avogadro’s number x no.of moles

Question 4

how is the no.of moles calculated?

Answer 4

n = mass ÷ mr

Question 5

how can we calculate the no.of moles in a solution?

Answer 5

n = conc x vol

Question 6

what is the ideal gas equation?

Answer 6

pV = nRT

Question 7

what is an ionic equation?

Answer 7

ionic equations show the ions that are formed in solution & show which particles are reacting

Question 8

what are titrations used for?

Answer 8

used to work out the conc of an acid / alkali

Question 9

describe the process of a titration

Answer 9

1. acid/alkali in burette with known conc
2. have acid/alkali with unknown conc but known vol in conical flask & add a few drops of indicator
3. add chemical in the burette to the conical flask until indicator changes colour (AKA end point), add drop by drop near end point
4. read how much chemical was added from the burette to neutralise chemical in conical flask. read at bottom of meniscus & always at eye level
5. record the results to 2 decimal places & repeat until 2 concordant results are produced

Question 10

what are concordant results?

Answer 10

results that are within 0.10 cm3 of each other

Question 11

give examples of indicators that can be used in a titration

Answer 11

phenolphthalein acid:
acid = colourless
alkali = pink

methyl orange:
acid = red
alkali = yellow

Question 12

define the term empirical formula

Answer 12

it’s the simplest whole number ratio of elements in a compound

Question 13

how is percentage yield calculated?

Answer 13

% yield = (actual yield ÷ theoretical yield) x 100

Question 14

what is the theoretical yield?

Answer 14

it’s the amount of a product produced assuming no products are lost & all reactants react fully

Question 15

what is atom economy?

Answer 15

it’s how efficient a reaction is

Question 16

how is atom economy calculated?

Answer 16

% atom economy = (molecular mass of a desired product ÷ sum of molecular masses of all reactants) x 100

Question 17

explain the importance of atom economy

Answer 17

1. high atom economies produce less waste - benefits the environment
2. high atom economies mean that raw materials are used more efficiently - more sustainable
3. higher atom economies mean fewer by-products so less time & money spent separating these from desirable products
4. companies will try to use reactions that tend towards 100% atom economy

Question 18

define the term hydrated compound

Answer 18

it’s a compound that contains water of crystallisation

Question 19

define the term anhydrous compound

Answer 19

it’s a compound that doesn’t contain water of crystallisation

Question 20

is the conversion of an anhydrous compound to a hydrous compound reversible & if so state the reaction required

Answer 20

yes it’s reversible - by heating the hydrated salt