Moles Flashcards
Formula for relative atomic mass
RAM = (abundance x mass) + (abundance x mass) /100
Percentage by mass formula
RAM of element we want / RFM of total compound x 100
What is the limiting reactant?
The reactant that limits the length of the reaction as it will all be used up before the other reactant runs out
What is the excess reactant?
The reactant that has more present than can actually be used up in the reaction
Moles formula
Moles = mass/molar mass
Percentage yield formula
% yield = actual/theoretical x 100
Why is actual yield less than theoretical yield?
- gas produced can escape/ leak out of equipment
- reactant may be impure
- gas may dissolve in water
- reaction may be irreversible
Formula for multiplier to get from empirical to molecular formula
Mr of molecule / Mr of empirical formula
dm3 to cm3
1dm3 = 1000cm3
Volume of a gas formula
Volume of gas = moles x molar gas volume
What is an anhydrous salt?
A dry salt without the water of crystallisation in it
What does the dot for water of crystallisation mean?
Water of crystallisation is loosely chemically combined with the rest of the compound
Describe the oxidation of magnesium practical
- measure + record mass of crucible and magnesium
- heat crucible with magnesium for several minutes, lifting the lid of the crucible up every min to allow oxygen to enter for complete combustion
- once the magnesium becomes a white solid, stop heating it, cool it and measure the mass
- repeat this process until the mass comes out the same twice in a row
Describe the reduction of copper oxide practical
- measure the mass of an empty reduction tube
- weight 2g of copper(II) oxide and add it to the reduction tube
- turn on the CH4 supply and flush the tube for at least 10 seconds
- light the Bunsen burner and heat the copper oxide for several minutes
- cool the apparatus + flush out the tube w methane
- record mass of reduction tube
Why is the reduction tube flushed out with methane before the reaction?
To remove oxygen, to prevent an explosion
