5. Formula and amounts (MOLE)
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What are amounts of substances measured in
Moles (mol)
What is Avagadro’s constant?
The number of atoms, molecules or ions (particles) in one mole of a substance. –> 6.02 x 10^23 mol-1
State Avagadro’s law
The volume of a gas is directly proportional to the number of moles of gas, when the temperature and pressure are held constant.
What is the molar mass of a substance
The molar mass is the mass per mole of a substance in g mol^-1
How do you work out the molar mass of a substance
Add up the relative atomic masses of all the elements in the molecule eg: CaCO3 - 40.1 + 12 + 16 + 16 + 16 = 100.1
Give the formula to work out the number/ amount of moles in a substance
moles (mol) = mass (g) / molar mass (g mol^-1)
How would you work out the number of particles or atoms in a substance from the number of moles it has
Moles ( mol) x avagadros constant
Give the equation to work out the concentration of a substance using the number of moles it has
concentration ( mol dm^-3 ) = moles (mol) / volume (dm^3)
How do you convert concentration in moldm -3 into gdm-3
Multiply the concentration by Mr
What is the molecular formula
The actual number of atoms of each element within a compound
What is the empirical formula
The simplest whole number ratio of the atoms of each element within a compound
Describe how to work out the empirical formula of a compound from experimental results and from percentages
1) Write out the mass of each element 2) Write down molecular mass (Mr) of each element 3) From the information above work out the number of moles using mass/ Mr 4) Divide all the numbers by the smallest number of moles 5) This will have produced a ratio of each element in the compound
what should you do if one of the ratios of the empirical formula ends in: 0.25 0.3 0.5 0.67
0.25 - times everything by 4 0.3 - times everything by 3 0.5 - times everything by 2 0.67 - times everything by 3
Give the 3 steps to form an ionic equation
1) write a balanced symbol equation, complete with state symbols 2) Add the charges to all the aqueous substances eg: NaCl becomes Na+ Cl- 3) Cancel out all the spectator ions (ions that remain same before and after reaction)
Give the equation for the relative atomic mass
(mass number of isotope 1 x relative abundance) + (mass number of isotope 2 x relative abundance) / by 100