Amount of Substance Flashcards
Define Avagadro’s Constant
The number of particles per mole
Define amount of substance
The quantity whose unit is the mole
Define mole
The amount of substance containing as many particles as there are carbon atoms in 12g of carbon-12
Define molar mass
The mass of 1 mole of any substance in of mol^-1
Define molar gas volume
The volume of 1 mole of any gas at RTP
Give the unit conversions for mass and volume
MASS
g to mg = x1000
kg to g = x1000
t to kg = x1000
VOLUME
m^3 to dm^3 = x1000
dm^3 to cm^3 = x1000
Give the five molar equations
moles = particles/avagadro
- particles may mean atoms, ions or molecules, you may need to multiply by how many there are
moles = mass/Mr
- solid, g for mass
moles = volume/24
- for a gas at RTP (298K and 100kPa), volume is dm^3
PV = nRT
- for a gas not at RTP
- p = Pa, v = m^3, T = Kelvin (add 273 to Celsius), n = moles, R = gas constant
moles = concentration x volume
- concentration can be written as molarity, volume is in dm^3
Give the equation that links mass, density and volume
mass = density x volume
How do you work out moles in a chemical equation?
- You need a balanced chemical equation
- Calculate the number of moles of one of the species using a molar equation
- Using the ratio, you can deduce the number of moles of all other species
How do you work out which is the limiting reagent in a chemical reaction?
- One reactant will be in excess (more than is needed)
- Workout which reactant is in excess by using ratio
- The limiting reagent will determine the moles of all other products
How do you work out the property of a substance from a chemical equation?
- Calculate moles of one of the species
- Deduce number of moles for other species using ratio
- Then you can calculate the property of another species using one of the molar equations
- Use limiting reagent to work out other moles if you get this sort of question
How do you work out reacting gas volume and therefore overall gas volume formed?
- Under same conditions of temp and pressure, volume of gas will only be affected by change in moles (volume of gas is proportional to moles)
- Therefore use ratio
What is atom economy?
A measurement of the percentage of atoms used in a reaction which are found in the desired product(s)
What does a higher atom economy mean?
Less waste
How do we improve atom economy?
- By-products may be sold or used for other purposes rather than sending them to landfill; costs less as disposal is expensive and is better for the environment so more sustainable
- Find a different synthetic route with a better atom economy
- Use lighter atoms where possible
What is the equation for atom economy?
Atom economy= Mr of desired products/ Mr of all products x100
What does the percentage yield tell us?
The percentage molar conversion of reactants to products
Give four reasons why percentage yield is normally less than 100%
- Incomplete reaction
- Side reactions
- Loss of product during washing or recrystallisation
- Loss of product transferring from one piece of equipment to another
Give the equation for percentage yield
Percentage yield= actual yield/ theoretical yield x 100
Give the steps for calculating percentage purity
- Work out moles of product
- Using the mole ratio from the balanced chemical equation work out the actual moles of reactant that must have reacted
- Using actual moles of reactant calculate the actual mass of reactant
- Work out percentage purity using equation (percentage purity= actual mass/ impure mass x 100
What should I do to the compound : FeN3O9
Simplify it to Fe(NO3)3
What does anhydrous mean?
Contains no molecules of water of crystallisation
What does hydrous mean?
Contains molecules of water of crystallisation
What does water of crystallisation mean?
.XH20 part of the formula of a hydrated salt. X meaning the number of moles of water relative to the number of moles of salt
Why do we have water of crystallisation?
Water molecules form an essential part of the crystalline structure of the compound
