The Mole

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Mole formula
Mole = mass over Ar
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A mole is
one mole of an element contains 6x10to the 23 atoms and has a mass in grams equal to the relative atomic mass
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Empirical formula is
The simplist/ smallest whole number ratio of the atoms of each element in a compound
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Molecular formula is
the actual number of atoms of each element in a compound
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To work out Empirical formula
Element I mass/g I Ar I mol=mass/Ar I divide by smallest mole
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Working out Molecular formula
Mr molecule over emprical formula, or Mr/EF
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Water of crystallisation
mass of water = mass of hydrated compound - mass anhydrous coompound
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Working out number of waters in hydrous compounds
Substance (compound, H2O mass) I mass/g I Mr I mol=mass/Mr I divide by smallest mol
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Working out reacting masses
1. Mole = mass/Mr 2. Deduce mole from Equation 3. Mass = molxMr
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Maths V Science
Only use no. sig figs qouted in question or 3s.f.
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Standard solution
A solution you know the exact concentration of, used for predicting strength of unknown concentrations
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mol =
mol = mass/ Mr
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Unit of concentration
mol dm-3
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Working out concentration
conc = mol/ vol
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Unit of Volume
Always in dm3, turn cm3 into dm3 by dividing by 1000
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Mol =
mole = conc x vol
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Workingout solution concentrations
1. mol = conc x vol 2. deduce no. moles using equation 3. conc = mol/ vol
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Monoprotic acid
Acid that produces 1 H+ ion per molecule. they react 1 to 1 with NaOH. HCL, HNO3
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Diprotic acid
Produces 2 H+ per molecule. react 1 to 2 with NaOH. H2SO4, H2C2O4 (ethanedioic acid)
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Triprotic acid
produces 3 H+ per molecule. React 1 to 3 with NaOH. H3PO4 (phosphoric acid)
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An equation
Na2CO3 + 2HCl --> NaCl + CO2 + H2O
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When original solution is 250cm3
Work out mol in the titration, usually 25cm3 (normal method) then x 10.
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When an excess of acid was used
Find out mol of unreacted acid; mol NaOH, mol to mol ratio, mol HCl then original mol - leftover = mol reacted
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Reasons for low % yield
1. impure substance at start. 2. unexpected side reactions 3. not fully reacted 4. some lost during experiment. 5. reversible/ equilibrium reaction so never 100%
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% yield equation
% yield = actual mass over max theoretical mass x100
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Theoretical mass
mass predicted by a mole calculation; mole, ratio, mass
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Atom economy
measures the overall use of all the atoms you purchase and use
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Why is atom economy important
1. want to be using as many atoms as possible from those purchased. 2. waste disposal expensive, so less waste is better.
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% atom economy equation
% atom economy = Mr of useful product / Mr total reactants x100
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Why all gases have the same volume
Because the volume is determined by the distance between molecules, not the size of molecules.
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Ideal gas equation
pV = nRT
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Converting degrees C into Kelvin
degrees C + 273 = degrees K, degrees K - 273 = degrees C
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T =
T = pV/nR
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n=
n = pV/ RT
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P =
nRT / V
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Unit of pressure
Pascals. x1000 = kPa. x1000000 = MPa
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Units of volume
m3 cm3 x 1000000 = m3. dm3 x 1000 = m3
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Calculating avogadro's constant
Avogadros number = mass of 1 mol over mass of 1 atom
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Percentage error for equipment
% error = + or - actual error / amount used x 100
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Burette error
= + or - 0.15cm3 / mean concordant value x 100
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Pippette error (10 cm3)
= + or - 0.04 / 10.0 x 100 = + or - 0.40%
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Pippette error (25 cm3)
= + or - 0.06 / 25.0 x100 = + or - 0.24%
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Balance error
= 0.02/ sample mass x 100
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Total apparatus error
= pippette error + burette error + balance error
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to reduce % error
1. use a balance of higher resolution 2. increase the mass.
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% error of the difference of two values
% error = dfference of values / actual value x 100
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Card 2

Front

A mole is

Back

one mole of an element contains 6x10to the 23 atoms and has a mass in grams equal to the relative atomic mass

Card 3

Front

Empirical formula is

Back

Preview of the front of card 3

Card 4

Front

Molecular formula is

Back

Preview of the front of card 4

Card 5

Front

To work out Empirical formula

Back

Preview of the front of card 5
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