Amount of Substance - Unit 1, Section 2

Question 1

what is a mole?

Answer 1

a unit used to measure amount of substance.

1 mole is 6.02 x 10*23 particles (Avogadro’s constant)

Question 2

Avogadro constant formula

Answer 2

number of particles = number of moles x Avogadro’s constant

Question 3

moles, mass, Mr equation

Answer 3

mass = Mr x moles

Question 4

moles and concentration equation

Answer 4

moles = conc x vol (cm3) / 1000
or
moles = conc x vol (dm3)

Question 5

ideal gas equation

Answer 5

pV = nRT

p = pressure = Pa
V = volume = m*3
n = number of moles
R = gas constant, 8.31 J K-1 mol -1
T = temperature = K

Question 6

empirical formula

Answer 6

gives the smallest whole number ratio of atoms of each element present in a compound

e.g: C4H302, CH20

Question 7

molecular formula

Answer 7

gives the actual numbers of atoms in a molecule

e.g: C8H604

Question 8

calculating empirical formulas

Answer 8

1. assume you have got 100g of the compound
2. turn the percentages straight into masses and then work out how many moles of each element are in 100g of the compound.
3. divide each number of moles by the smallest number of moles you found in the step above. this gives you the ration of the elements in the compound.
4. apply the numbers from the ratio to the formula.

Question 9

what is theoretical yield

Answer 9

the mass of product that should be formed in a chemical reaction.

it assumes that no chemicals are lost in the process.

Question 10

calculating theoretical yield

Answer 10

1. work out how many moles of the reactant you have
2. use the equation to work out how many moles of product you would expect that much reactant to make.
3. calculate the mass of that many moles of product and that’s the theoretical yield. (moles x Mr)

Question 11

calculating percentage yield

Answer 11

% yield = actual yield/ theoretical yield x 100

Question 12

what is atom economy?

Answer 12

a measure of the proportion of reactant atoms that become part of the desired product in the balanced chemical equation.

Question 13

calculating atom economy

Answer 13

% atom economy = Mr of desired products / Mr of all reactants x 100

Question 14

economic advantages of high atom economy

Answer 14

• makes more efficient use of raw materials
• more cost effective
• less waste to dispose of, less cost to do this

Question 15

environmental and ethical advantages of high atom economy

Answer 15

• fewer raw materials and less waste is better for the environment as chemicals are often harmful and materials are in limited supply
  -tends to be more sustainable
  -can be good for society if companies use cheaper ways to mass produce products as it could mean they are sold cheaper and can be made more available to people.