Amount of Substance

Question 1

Relative Atomic Mass (RAM or Ar)

Answer 1

Average mass of one atom of an element/ 1/12 of 1 C-12 atom

Question 2

Relative Molecular Mass (RMM or Mr)

Answer 2

Average mass of one molecule/ 1/12 Ar of 1 C-12 atom

Question 3

How do you calculate Mr?

Answer 3

Add up all the atomic masses of the atoms that make up the molecule

Question 4

Relative Formula Mass (RFM or Mr)

Answer 4

• Used for ionic compounds as they don’t form as molecules
• Calculated the same way as relative molecular mass
• Uses the same symbol as RMM (Mr) because of this

Question 5

Avogadro’s Constant (The Mole)

Answer 5

• 6.022x10^23
• Units are mol-1
• Known as a mole

Question 6

Moles Equation

Answer 6

Moles = Mass/Mr

Question 7

Empirical Formula

Answer 7

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

Question 8

How is empirical formula calculated?

Answer 8

• Find the masses of each element in each compound
• Work out the number of moles of atoms of each element (Mass/Ar)
• Convert the number of moles of each element into a whole number ratio

Question 9

Molecular Formula

Answer 9

The actual number of atoms of each element in one molecule of a compound

Question 10

How is Molecular Formula calculated from Empirical Formula?

Answer 10

• Divide the Mr of the molecular formula by the Mr of the empirical formula
• Multiply out the formula by the number you get

Question 11

How do you calculate the formula of an ionic compound?

Answer 11

• Write down ionic symbols and charges of the elements within the compound
• Swap over the charges
• Cancel to the lowest whole number ratio if necessary

Question 12

Atom Economy

Answer 12

A measure of the percentage of reactants that become useful products

Question 13

Percentage Atom Economy Equation

Answer 13

(Mr of desired product/Total Mr of Reactants) x100

Question 14

Can the percentage of an atom economy be increased?

Answer 14

• Technically you can’t raise the atom economy of a particular product
• However you can find uses for the waste products
• This increases the atom economy of all the products

Question 15

Percentage Yield

Answer 15

How much reactant has successfully been converted into product in a chemical reaction

Question 16

Percentage Yield Equation

Answer 16

Actual yield/Theoretical yield

Question 17

Ideal Gas Equation

Answer 17

PV = nRT
- Pressure is in Pascals (Pa)
- Volume is in m3
- Gas Constant is in JK-1MOL-1
- Temperature is in Kelvin (add 273 to the degrees celsius)