Topic 5: Formulae, Equations & Amounts of Substance 1️⃣&2️⃣
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Define : mole
A mole is the amount of a substance that contains the same number of carbon atoms in exactly 12g of the carbon-12 isotope
What is Avogadro’s constant
Number of atoms of carbon-12 in exactly 12g of carbon-12 (6.02 x10^23)
What is the molar mass? (M)
The mass per mole of the substance in g mol-1
What is the empirical formula?
Smallest whole number ratio of the atoms of each element in a compound
What is the molecular formula?
The actual number of atoms of each element present in a compound
When do you use the ideal gas equation instead of the molar volume triangle?
When the gas isn’t at room temp and pressure
Define net ionic equation
A simplified ionic equation that shows only the species involved in the chemical reaction
What does the big N in the avogadro triangle stand for
Number of particles Once you calculate this if it asks for number of atoms/ ions , multiply by the amount of species present eg. C2H4 is 2+ 4 = 6 so x6
What is the molar volume
The volume of gas that contains one mole of that gas at room temp and pressure one mole of gas will occupy 24dm^3
Define: solute
A substance that is dissolved
Define solvent
A substance that dissolves a solute
Define solution
A solute dissolved in a solvent
Primary standards will ideally be…
Chemically stable Not absorb or react easily with substances in the atmosphere Be soluble in water React quickly and steadily with other solutions Be inexpensive Have a high degree of purity Solids with a high molar mass
Describe the steps in making a standard solution
Find the mass of solute needed Add approximate mass of solute to weighing boat and transfer as much as possible to the beaker Reweigh the weighing boat to improve accuracy Calculate the actual mass of solute Add deionised water to beaker and dissolve solute using a stirring rod Wash the stirring rod with distilled water over the beaker to catch traces Place the funnel into the volumetric flask and pour in solution Rinse the beaker over the funnel with distilled water, catching rinsings in the flask Add deionised water to the graduation mark on the flask Add stopper and invert multiple times to mix
What is an error
Something that affects results, which was not plausible to avoid or account for (given the conditions of the experiment) Therefore accounts for the difference between an experimental value and the correct value
What is a mistake
Something that affects the results, which should reasonably been avoided
Define accuracy
A measure of how close the values are to the accepted/correct value
Define precision
A measure of how close the values are to each other
Define random error
Errors caused by unpredictable variations in conditions
Define systematic error
Errors are constant and predictable, usually due to the apparatus being used
Define measurement uncertainty
The potential error involved when using a piece of apparatus
Define theoretical yield
The maximum possible mass of a product in a reaction assuming a complete reaction and no losses
Define actual yield
The actual mass of a product obtained in a reaction
Why is it very rare to get 100% yield
Reaction may be at equilibrium and therefore never reach completion Side reactions could occur producing by-products Impure reactants Reactants or products left behind in previous apparatus