Amount of Substance (not done)

Question 1

What is relative atomic mass (Ar)?

Answer 1

the weighted mean mass of an atom of an element, compared to 1/12th the mass of an atom of carbon-12

Question 2

What is relative formula/molecular mass (Mr)?

Answer 2

the average mass of a molecule or formula unit compared to 1/12th the mass of an atom of carbon-12

Question 3

What is relative isotopic mass?

Answer 3

the mass of an atom of an isotope, compared to 1/12th of the mass of an atom of carbon-12

Question 4

How do you calculate relative atomic mass (Ar) of an element from its isotopic abundances?

Answer 4

Ar = [(Isotope 1 mass x % abundance) + (Isotope 2 mass x % abundance)] / total % abundance (100)

Question 5

What is amount of substance (n)?

Answer 5

number of particles in a substance

Question 6

What is a mole and what is Avogadro’s constant?

Answer 6

unit for measuring amount of substance
1 mole = 6.02 x 10^23 particles
(multiplying moles by this constant gives you the number of particles)

Question 7

What is molar mass?

Answer 7

the mass of 1 mole
same as the relative formula mass
units = gmol-1

Question 8

What is the formula to find moles (involving mass)?

Answer 8

number of moles = mass/Mr

Question 9

What is molar gas volume?

Answer 9

the space that one mole of a gas occupies at a certain temperature and pressure
units = dm3 mol-1

Question 10

Do gases take up the same volume under the same conditions?

Answer 10

yes

Question 11

What is the molar gas volume at rtp?

Answer 11

24 dm-3 mol-1

Question 12

What is the formula to find moles (involving molar gas volume)?

Answer 12

number of moles = volume in dm3/molar gas volume

Question 13

What is the ideal gas equation?

Answer 13

pV = nRT
- p = pressure (Pa)
- V = volume (m3)
- n = number of moles (mol)
- R = gas constant (8.314 J K-1 mol-1 don’t need to learn)
- T = temperature (K)

Question 14

Things to be careful of in the ideal gas equation:

Answer 14

in K not °C
in m3 not dm3
in Pa not kPa

Question 15

How do you find temperature in Kelvin from temperature in Celsius?

Answer 15

K = °C + 273

Question 16

What is an empirical formula?

Answer 16

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

Question 17

What is a molecular formula?

Answer 17

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

Question 18

How do you calculate empirical/molecular formula from composition by mass/% compositions by mass?

Answer 18

• always try and work out moles using what you’re given
• finding the ratio of those moles = empirical formula
• comparing the molecular mass by the empirical mass will tell you what the molecular formula is