chapter 3 - amount of substance and the mole
Cards (23)
- one mole is the amount of a substance that contains as many particles as there are atoms in 12g of carbon-12 (avagadros constant)
- molar massthe mass per mole of a substance
- units of molar massgmol-1
- moles = mass / molar mass
- empirical formulasimplest whole-number ratio of atoms of each element in a compound
- steps to work out empirical formula
- divide the percentages, by molar mass
- divide this by the smallest of the numbers
- this is the ratio
- relative molecular masscompares the mass of a molecule with the mass of an atom of carbon-12
- relative formula masscompares the mass of a formula unit with the mass of an atom of carbon-12
- when blue crystals of hydrated copper sulfate are heated, bonds holding the water within the crystal are broken and the water is driven off, leaving behind white anhydrous copper sulfate
- assumptions made for water of crystallisation
- all the water has been lost - solution, to heat to constant mass
- no further decomposition - solution, heat gently
- 1 dm3 = 1000 cm3 = 1000 ml = 1L
- moles = concentration x volume
- a standard solution is a solution of known concentration
- molar gas volume is the volume per mole of gas molecules at a stated temperature and pressure
- RTP is 20 degrees and 101 KPa
- one mole of gas = volume / 24
- ideal gas equation assumption
- random motion
- elastic collisions
- negligible size
- no intermolecular forces
- ideal gas equation:pV = nRT
- stochiochemistry is the balancing of numbers to give the ratio of an amount, in moles, of each substance
- percentage yeild = moles of actual yeild / moles of theoretical yeild
- atom economy = moles of desired products / moles of all productsx 100
- Reaction with high atom economies:
- produce a large proportion of desired products and few unwanted waste products
- are important for sustainability as they make the best use of natural resources
- efficiency and sustainability depends on both percentage yeild and atom economy