RAMs and moles *

Question 1

what is the carbon-12 scale?

Answer 1

masses of atoms are compared to the mass of a carbon-12 isotope

Question 2

how do you calculate the average mass of an atom?

Answer 2

(abundance amount x mass no.) + (abundance amount x each isotope) / total abundance

Question 3

What is the RAM?

Answer 3

Relative Atomic Mass

the weighted mean mass of an atom of an element on the carbon-12 scale (relative to 1/12th of the mass of an atom of carbon-12)

Question 4

what is the relative isotopic mass?

Answer 4

the mass of an atom of an isotope on the carbon-12 scale (relative to 1/12th of the mass of an atom of carbon-12)

Question 5

How do you find the RAM of one atom?

Answer 5

RAM of one atom = (RAM of isotope 1 x % of isotope 1) + (RAM of isotope 2 x % of isotope 2) / 100

(eg.magnesium)

magnesium contains:
78.6% of 24Mg
10.1% of 25Mg
11.3% 26Mg
(100 atoms of magnesium 78.6 atoms will be 24Mg, etc)

total mass of 100 atoms = (78.6 x 24) x (10.1% x 25) + (11.3 x 26) = 2432.7
average mass of 1 atom = 2432.7 / 100 = 24.3

Question 6

What is the RFM?

Answer 6

Relative Formula Mass, can also be Relative Molecular Mass (RMM), or Mr

the sum of all the masses of all the atoms in one formula unit of an element or compound

Question 7

How do you calculate the RFM?

Answer 7

add together the RAMs for all of the individual atoms in that compound

Question 8

(Conservation of mass) Fill in the gaps :

• In any reaction, there may be a change of _____, a change in ___________ or a new _______ formed
• The mass of the ________ will always be _____ to the mass of the _______
• A _______ equation means that there is ___________ __ ____

Answer 8

• In any reaction, there may be a change of state, a change in temperature or a new product formed
• The mass of the reactants will always be equal to the mass of the products
• A balanced equation means that there is conservation of mass

Question 9

Give 4 key points about a precipitation reaction

Answer 9

• An example of conservation of mass
• Transition metals form coloured compounds with other elements
• Many of these are soluble in water, forming coloured solutions
• They can also form solid precipitates

Question 10

what is a mole?

Answer 10

a measure of the number of particles in a substance (in grams)

Question 11

What is the specific number used (a mole)

Answer 11

Avagadro’s number
6.02 x 10(to the 23)

Question 12

How do you calculate the number of moles?

Answer 12

number of moles = mass (g) / RAM

Question 13

How do you calculate the weight of 1 mole?

Answer 13

• find the RAM or RFM and add units (grams)
  eg. mass of 1 mole of carbon is 12g

Question 14

How do you calculate the mass of a number of moles?

How do you calculate the number of moles?

Answer 14

mass (g) = mass of 1 mole x number of moles

number of moles = mass (g) / mass of 1 mole

Question 15

How do you calculate moles to particles?

Answer 15

number of moles x avagadros number / 1
(6.02x10tothe23)

Question 16

What is the empirical formula?

Answer 16

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

Question 17

How do you find the empirical formula?

Answer 17

1) divide mass by the RFM to find number of moles
2) simplify the ratio

(eg. ethane)

• in ethane there are 2 Cs and 6 Hs
• the ratio of C:H would be 2:6
• the simplest ratio is 1:3
• so the empirical formula is C(1)H3

Question 18

what is the molecular formula?

Answer 18

the formula showing the actual number of atoms of each element in a molecule of a compound

Question 19

How do you convert the empirical formula into the molecular formula?

Answer 19

1) find the number of atoms of each element
2) find the sum of their RFMs
3) find the conversion factor - divide the RFM for the molecular formula by the RFM for the empirical formula)
4) multiply sum of RFMs by conversion factor

Question 20

How do you find the number of particles?

Answer 20

moles x avagadros number (6.02 x 10 to the 23)