Calculations Flashcards
What is the relative fromula mass
The relative formula mass of a compound is the relative atomic masses of all the atoms in the compound added together
What is a mole equal to
The RFM of a compound
What is empirical formula
The smallest whole number ratio of atoms in the comoumd
Equation for percentage mass of a compound
(RAM x number of atoms of that element/RFM of compound) x100
What is molecular formula
a chemical formula that gives the total number of atoms of each element in each molecule of a substance
Equation for number of moles
Mass in g (of element/compound) / RFM (of compound) or RAM (of element)
What is avagadros constant
6.02 x 10 to the power of 23
What is concentration
Thr measure of how crowded things are
What is concentration measured in
g dm(-3)
Equation for concentration
Mass/volume
Steps on how to work out the empirical formula from the masses of the elements it contains
1) work out how many moles of each element you have (moles = mass/Ar)
2) work out the smallest whole number ratio between the moles of the elements to get the empirical formula
Steps on the experiment on how to calculate the empirical formula of a metal oxide - magnesium oxide
1) get a crucible and heat till very hot to get rid of any traces of left over oil and water
2) leave the crucible to cool then weigh it and it’s lid
3) add some clean magnesium ribbon to the crucible, reweigh the crucible lid and magnesium ribbon. The mass of the magnesium you’re using is the reading minus the first reading
4) heat the crucible containing the magnesium, put the lid on the crucible to stop any bits escaping but leave a little gap to allow oxygen to enter
5) heat crucible strongly for about 10 mins or until all magnesium ribbon has turned white
6) allow crucible to cool and reweigh with lid and contents. Mass of magnesium oxide is this reading minus the initial reading for the mass of crucible and lid
