# The Mole

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- Created by: bio1423
- Created on: 05-11-13 19:26

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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## Other cards in this set

### 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

### Card 4

#### Front

Molecular formula is

#### Back

### Card 5

#### Front

To work out Empirical formula

#### Back

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