Topic 5: Formulae, Equations & Amounts of Substance 1️⃣&2️⃣ Flashcards
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
Why do we use atom economy?
Considers not only the desired products but also the by-products, describing the efficiency of a reaction in terms of all atoms involved
Encourages companies to reduce waste
Acid + metal ——>
Salt + hydrogen
(Classified as neutralisation and redox)
Metal oxide + acid ——>
Salt + water
(Neutralisation)
Metal hydroxide + acid —->
Salt + water
(Neutralisation)
What is a displacement reaction
Chemical reactions in which a more aq metal (one which more readily loses electrons) displaces a less reactive metal from an aq solution of one of its salts
All displacement reactions are REDOX
How does reactivity change as you go down group 7 (halogens)
Reactivity decreases down the group
What are the uses of halogen displacement
Purification of water
Production of halogenated compounds
What is a precipitation reaction
Substances in a solution are mixed and an insoluble product is formed.
The insoluble product is called a precipitate and can be seen as a solid forming in the reaction mixture
What does qualitative mean
Measuring non-numerical data
Allows us to understand the characteristics of substances
What does quantitive mean?
Measuring numerical data
Allows us to find kamounts’
Describe a concentration test
Form precipitate, centrifuge, collect pellet, measure mass, calculate conc
Describe a cation test
Flame tests
OR
add NaOH - precipitate forms, qualitative colour analysis :
Green= iron (II)
Brown= iron (III)
Blue = copper
If white, add excess NaOH , still white ? Aluminium, gone colourless? Calcium
Acid + base ——>
Salt + water
Acid + metal carbonate —->
Metal salt + carbon dioxide + water
