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
