Stoichiometric Calculations Flashcards
What is stoichiometry the study of
Stoichiometry is the study of mole relationships involved in chemical reactions.
What is the mass of a mole of any substance equal to
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.
Precipitation % by mass calculation
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
Percentage yield
Use percentage yield formula for find theoretical
Use theoretical to find n
Mole ratio
N=mxgfm
The percentage yield is reduced by:
♦ mass transfer or mechanical losses
♦ purification of product
♦ side reactions
♦ equilibrium position
Back titration steps
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
How to work out the mass of a reactant
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
How do your rearrange to work out actual of product
A = T x % / 100
What do you sometimes have to do in percentage yield
Work out excess and limiting before substituting into the eqn
Percentage by mass is the mass of solute made up to 100 cm3 of solution.
a 1% starch indicator solution contains 1g of starch dissolved deionised water and the
solution made up to 100cm3 with deionised water.
Percentage by volume is the number of cm3 of solute made up to 100 cm3 of solution
A 10% ethanol solution contains 10cm3 of ethanol and the solution made up to 100cm3
with deionised water.
