Topic 3

Question 1

What is a mole

Answer 1

mol = 6.022 x 1023 entities
- Entities can refer to atoms, molecules, ions, cars
chickens, moles (furry blind creatures), eggs etc.
- E.g. → 1 mol Ne contains 6.022 x 1023 atoms

Question 2

SIGNIFICANCE OF NUMBER 6.022 x 1023 ?

Answer 2

• There are 6.022 x 1023 atoms in 12 g carbon‐12
• 1 mol = amount of a substance that contains the same no. of
  entities as there are atoms in 12 g carbon‐12
  o 6.022 x 1023 is Avogadro’s number (N)

Question 3

Atomic mass

Answer 3

is calculated as the
average of the masses of its commonly occurring isotopes
weighted according to their natural abundance

Question 4

o Atomic mass unit (amu)

Answer 4

• Mass of an atom measured relative to the mass of an atomic
  standard
• The standard is the carbon‐12 atom (6 protons & 6 neutrons)
• 1 amu = 1/12 of the mass of a carbon ‐12 atom

Question 5

o MOLAR MASS (M)

Answer 5

o Conversion between mole, mass & molar mass
→ simply look at the units
→ dimensionally homogeneous

n=m/M

Question 6

RELATIONSHIP BETWEEN ATOMIC MASS,
MOLES & MOLAR MASS. (per molecule)
C6H12O6:
1. no. Atoms
2.moles of atomes
3.no. atoms per a mole
4.mass
5.mass per mole

Answer 6

Question 7

Law of mass conservation

Answer 7

→ equaƟon must be balanced
→ number of atoms of each element must be conserved

Question 8

REACTIONS IN SEQUENCE
Multi‐step Reactions

Answer 8

1. Write the sequence of balanced equations.
2. Adjust the equations arithmetically to cancel the common
   substance(s).
3. Add the adjusted equations together to obtain the overall
   balanced equation.
   N.B. Only if the product from reaction is a reactant in the next
   step!!!!

Question 9

o LIMITED REACTANT:

Answer 9

Reactant that is consumed first
- Limits the amount of other reactant(s) that react to form
product
- Other reactant(s) in excess

Question 10

General approach for solving any stoichiometry problem:
* What to check check first
* convert what to what

Answer 10

1. Write a balanced equation for the reaction.
   i. Translating the statement into a “skeleton equation”.
   ii. Balancing the atoms with a stoichiometric coefficient.
   iii. Adjusting the coefficients to the smallest whole-number coefficients.
   iv. Specifying the states of matter: (g), (l), (s), (aq).
2. Convert the given mass of the first substance to a mol amount.
3. Use the appropriate molar ratio from the balanced equation to calculate
   the amount (mol) of the second substance.
4. Convert the amount of the second substance to the desired mass

Question 11

o THEORETICAL YIELD:

Answer 11

If 100% of the limiting reactant is converted to product
- Never actually achieved due to side reactions occurring,
incomplete reaction, incomplete separation methods etc.

Question 12

o ACTUAL YIELD:

Answer 12

• The actual amount of product obtained

Question 13

o ACTUAL YIELD:

Answer 13

• The actual amount of product obtained

Question 14

PERCENTAGE YIELD:

Answer 14

• Actual yield expressed as a percentage of the theoretical
  yield
• % yield = (actual yield / theoretical yield) x 100%

o FOR MULTI‐STEP REACTIONS:
- The overall % yield equals the product of the stepwise yields

Question 15

Calculate overall yield

Answer 15

Multiply each yield from reaction

And NB cannot be higher than individual yield of each reaction