Formulae And Amounts Of Substances Flashcards
Definition of molecular formula
Formula which shows the actual number if atoms of each element in a molecule
Definition of empirical formula
Formula which shows the simplest WHOLE NUMBER ratio of atoms of each element in a compound
Definition of molar gas volume
The volume of one mole of gas under specified conditions of temperature and pressure
Eg 24dm^3 at 20C and one atmospheric pressure
How do you calculate the empirical formula
Divide the masses/% masses by the RFM of the element
Divide all answers by the smallest answer
Write out the formula (may have to multiply by a certain number in order to get a WHOLE NUMBER ratio)
How do you work out the molecular formula?
- Empirical formula calculated
- Divide RFM by empirical formula ➡️ gives scale factor
- Multiply all numbers in empirical formula by this scale factor
Write the combustion equation
See notes
How do you work out the number of moles of a gas (mol)
Volume of gas (dm^3)
——————————
Molar volume (dm^3 mol^-1)
How do you work out the volume of a gas?
Moles of gas x 24 (vol in dm)
How to figure out an unknown hydrocarbon
Burn completely in oxygen and measure volume of everything
What does NaOH do in combustion questions?
Absorbs CO2
How to work out unknown volume of O2 in combustion hydrocarbon Qs
See equation pg 14 ALL IN VOLUMES
What is the theoretical yield
Max possible amount of products formed from the reactants used
Reasons for theoretical being more than the actual yield
Impure reactants
Reaction may not go to completion
Competing side reactions
Product left in container
Percentage yield equation
(Actual yield/theoretical yield) x 100
What is atom economy an indication of
Measure of efficiency of converting reactants to desired products
Can be used to compare efficiency of diff reactions
High % ➡️ more efficient and less waste
