Topic 5: Formulae And Calculations
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State the definition for a mole
The unit for an amount of substance
State the definition for a molar mass of a substance
The molar mass of a substance is its mass per mole of the substance in g/mol-1
State Avagadro’s constant
6.02x10^23 mol-1
What is the difference between molecular and empirical formula?
Empirical shows the relative number of atoms of each element using the smallest whole numbers. Molecular formula gives the actual number of atoms of each element in a molecule.
State the ideal gas equation and the units for each symbol
pV=nRT P= pressure in Pa V= in m^3 R= 8.314 J K-1 mol-1 T= temperature in kelvin OR if pressure is KPa, volume MUST be dm^3
How do you work out the temperature in Kelvin?
Take the temperature in degrees Celsius and add 273
Give the formula for finding particles
Particles= n x L
State the symbols and charges for Zinc, silver, ammonium and hydrogencarbonate ions
Zn 2+ Ag+ NH4+ HCO3-
What is the difference between ide and ate endings?
Ide Endings mean it only contains the named compounds Ate Endings mean there is something else, often oxygen
How do you work out percentage yield?
Actual yield/theoretical yield X 100
How do you work out atom economy?
Molar mass of the desired product/sum of molar masses of all products X 100
How do you calculate percentage uncertainty/percentage error?
Percentage error= uncertainty/reading X 100 The uncertainty is half a division on either side of the smallest unit on the scale you are using
What is the uncertainty associated with a two decimal place balance reading?
+- 0.005g The uncertainty associated with the difference between two balance readings is 2 x 0. 005= +-0.01g
What’s the uncertainty associated with a volumetric flask, Burette and pipette reading?
± 0.2cm^3 for a flask ± 0.6cm^3 for a pipette ± 0.05cm^3 for a burette
How do you calculate Ar?
(% x mass of A) + (% x mass B) / total % The total % is usually 100
What is the idea of conservation of mass?
Total mass before = total mass after a reaction
How do you find moles using mass?
m = n x Mr