topic 3: calculations Flashcards
(12 cards)
how do you use the mass = moles x Mr equation?
- RTQ
- sub the digits you know into the equation
3.use the ratio (think of it like a fraction: divide by the start number and multiply by the end number) - convert the moles into the required units
how do you calculate the percentage mass of an element in a compound?
mass of element/ mass of compound(Mr) x100
what’s the conversion of dm^3 to cm^3?
1 dm^3 = 1000cm^3 (x 1000)
what are the TWO equations for gases and moles
gas volume(cm^3) = moles x 24,000
gas volume (dm^3) = moles x 24
(if its cm^3 x 24,000 if its in dm^3 x 24)
name the units of concentration
mol/dm^3
what is the equation for solutions and concentrations?
concentration (mol/dm^3) = mol/volume (dm^3)
if the volume is in cm^3, divide it by 1000 to make it dm^3
what is the equation to calculate percentage yield?
actual yield or experimental yield = how much product you actually make (given to you in the question)
theoretical yield or maximum yield = how much can be made if it is fully reacted ( what you work out from mole calculations)
percentage yield = actual yield / theoretical yield (should always be less than 100)
what factors mean the actual yield doesn’t produce as much as the theoretical yield?
Incomplete Reactions:
Not all of the reactants may react
Side Reactions:
Other reactions can occur alongside the main reaction
Losses during Product Recovery:
During processes like filtration, transfer, washing, and drying, some of the product can be lost
Impurities in Reactants:
Reactants may not be 100% pure.
Equilibrium Limitations:
In reversible reactions, the reaction may reach equilibrium before all the reactants are converted into products, limiting the yield.
Measurement and Experimental Errors:
Errors in measuring reactants or products, and limitations of the experimental apparatus
what is the empirical formula?
Empirical formula = simplest whole-number ratio of atoms
Molecular formula = actual number of atoms in a molecule
how do you calculate the empirical formula?
- RTFQ
- use the table method
- separate out each element with their masses or percentages in the column below
- calculate the moles using mass/Mr x moles
- ratio the moles
- multiply up if needed to calculate the simplified ratio
- write down the empirical formula
how do you calculate the molecular formula from the empirical formula?
- calculate empirical formula using the tablev method
- work out the total Mr of the empirical formula
- Mr of molecular formula/mr of empirical formula
- multiply the empirical formula by the the number you get from the fraction
example: an organic compound has the empirical formula of CH2 and an Mr of 28. what is the molecular formula?
mass of CH2 = (12+2x1) = 14
28/14 = 2
CH2 x 2 = C2H4
how do you calculate water of crystallisation?
use the table method similar to calculating the empirical formula
- list all of the salts and water in the table
- calculate the Mr beneath them
- using their experimental masses, calculate there moles
3.simplify the ratio by dividing by the smallest
- write out your formula
note: answer should always be between 1 and 12
