Stoichiometric Calculations

Question 1

What is stoichiometry the study of

Answer 1

Stoichiometry is the study of mole relationships involved in chemical reactions.

Question 2

What is the mass of a mole of any substance equal to

Answer 2

The mass of a mole of any substance, in grams (g), is equal to the gram formula mass
(GFM) and can be calculated using relative atomic masses.

Question 3

Precipitation % by mass calculation

Answer 3

Work out ion and precipitate

Use last mass and GFM of precipitate for number of moles

How many of the ion are in the precipitate

Scale to standard flask

M=nxgfm

Mass / sample x100

Question 4

Percentage yield

Answer 4

Use percentage yield formula for find theoretical

Use theoretical to find n

Mole ratio

N=mxgfm

Question 5

The percentage yield is reduced by:

Answer 5

♦ mass transfer or mechanical losses
♦ purification of product
♦ side reactions
♦ equilibrium position

Question 6

Back titration steps

Answer 6

Step 1: Moles of titrant. 1
Step 2: Excess moles. Smaller volume 2
Step 3: Added moles. Larger volume. 2
Step 4: Reacted moles = added - excess. 2
Step 5: Moles of substance. 3
Step 6: Mass of substance. 3

Question 7

How to work out the mass of a reactant

Answer 7

To work out Theoretical
1. Entity
2. Mole ratio
3. × by gfm
4. Scale for mass of Product given
To work out mass of reactant needed:
1. Make Theoretical mass = % yield given
2. Scale for 100% yield