3.1.2 - amount of substance Flashcards
how to convert from molar concentration to mass concentration?
mass concentration / Mr
define relative molecular mass (Mr)
the average mass of a molecule relative tot 1/12 of the mass of an atom of carbon-12
define relative atomic mass (Ar)
the weighted masses of all the isotopes of an element relative to 1/12 of the mass of an atom of carbon-12
define the mole of a substance
the amount of that substance that contains the same number of particles as there are atoms in 12g of carbon-12
how to convert from m^3 to dm^3
m^3 X 1000
how to convert from cm^3 to dm^3
cm^3 divided by 1000
why must air bubbles be removed from burettes and pipettes?
presence of air bubbles means that the titre read will be a higher volume, as it seems like there is a higher volume in the burette/pipette
why must the connical flask be rinsed with distilled water during a titration?
- gets all the reactants into the flaks to react
- doesn’t affect the titre, as the moles stay the same
why must only 3 drops of indicator be added to the conical flask?
- indicators are acids, so could increase the pH.
- this could affect the titre value
why must burettes and pipettes be rinsed with appropriate solutions?
- rinse equipment with whatever is going into them
- this ensures no residue is left from other solution
- what is the molecular formulae
- what is the empirical formulae
- the actual number of each element in a compound (C8H18)
- the simplest whole number ratio of atoms in each element in a compound (C4H9)
describe how to calculate empirical formulae of a compound
- find mass of each element per 100g
- calculate moles (mass/Mr)
- divide by the smallest mole value to find the ratio
- write formula using ratio
state the ideal gas equation
pV = nRT
state the values and units in the ideal gas equation
- pressure (Pa)
- volume (m^3)
- number of moles
- gas constant (8.31Jk -1 mol -1)
- temperature (K)
how to convert cm^3 to m^3
cm^3 / 1X 10^6
how to convert °C to K
+ 273
explain what is meant by a hydrous compound
compound that contains water molecules that are bonded into its crystalline structure
how is a hydrous compound changed into an anhydrous compound ?
heated up
explain what is meant by uncertainty
interval within which the true value can be expected to lie
- define resolution
- state resolutions relationship with uncertainty
- how small a instrument can measure
- smaller resolution = lower uncertainty
explain what must be done to the uncertainty when taking a measurement (e.g. from a burette)
- multiply the uncertainty by 2
- because 2 judgements must be read
explain how to calculate uncertainty
- half the smallest possible unit you can make
- balances smallest unit = 0.01g
- uncertainty = 0.01g / 2
- uncertainty = +/- 0.005g
state how to calculate percentage apparatus uncertainty
( uncertainty for piece of apparatus / measurement value ) x 100
state how to calculate actual experiment percentage uncertainty
( difference between actual and recorded values / actual value ) x 100
what does it mean if actual experiment % uncertainty is lower than % uncertainty for apparatus
the difference is due to apparatus
what does it mean if actual experiment % uncertainty is larger than % uncertainty for apparatus
the difference is due to human error
state 4 reasons why actual yield could be lower than theoretical yield
- not recovering all of the product
- impurities
- side reactions occurring
- reaction is incomplete (e.g. reversible reactions)
state the equation for percentage yield
( actual yield / theoretical yield ) x 100
state the equation for atom economy
( Mr of useful product / Mr of total products ) x 100