Note
0.0(0)

1.2 amount of substance (notes)


relative atomic mass (Ar)

  • the mean mass of an atom of element, relative to the mass of 1/12th of the mass of an atom of the 12C isotope



average mass of an atom of an element x 12

mass of one atom of 12C


or


∑ (isotope abundance x isotope mass number) x 100

∑ (isotope abundance)



relative molecular mass (Mr)

  • the mean mass of a molecule of a compound relative to 1/12th of the mass of an atom of the 12C isotope



relative formula mass


the sum of the relative atomic masses of the atoms in the chemical formula of a compound

  • ionic compound have a giant ionic lattice with a very large number of ions, so the relative formula mass is the Mr of the empirical/chemical formula



the mole:

  • a unit of measurement that represents a specific quantity of a substance

  • it is the amount of pure substance that contains the same number of particles as there are in exactly 12g of 12C

  • 1 mole of a substance contains 6.022 × 1023 molecules/atoms/ions

    • Avogadro’s constant, L

    • there are 6.022 × 1023 atoms of 12C in 12g of 12C


no. of molecules = nL


n = mass/Mr


n = cv


molarity = moles per dm3 = concentration in moldm-3


molar mass = the mass of one more of a substance = Mr or Ar



gases and volatile liquids follow the ideal gas equation under standard conditions

pV = nRT


p = pressure in Pa


V = volume in m3

m3 ← ÷1000 — dm3 ← ÷1000 — cm3


n = amount in moles


R = ideal gas constant = 8.314 J K-1 mol-1


T = temperature in K

°C —+273 → K



p is proportional to V

V is proportional to T

p and V are inversly proportional



assumptions:

  • gas molecules move randomly

  • there are no forces acting between gas molecules

  • gas molecules are tiny compared to the spaces between them

  • collisions between gas molecules are elastic



1 mole of a gas at room temp = 24 dm3

volume = n x 24 dm3


room temperature = 25°C = 298 K

room pressure = 101 325 Pa ≈ 101 00 Pa = 101k Pa = 1 atmosphere


empirical formula = the simplest whole number ratio of the atoms of each element in a compound


molecular formula = the true number of atoms of each element in a compound


a molecular formula is not practical for giant crystal structures because giant lattices contain a vast number of atoms of each element, and larger crystals will have more atoms than smaler crystals


percentage yield: a measure of the efficient conversion of reactants to products / idea of getting as much product as possible in the reaction

  • (mass of product actually made / maximum theoretical mass of product) x 100


percentage yield may be low if:

  • the product is gas so easily escapes

  • impure reactants are used which cause side products OR not all reactants react (especially in reversible reactions)

  • there are side reactions making other products/there are by-products

  • some of the product is lost during filtration/separation/transferring



atom economy: maximising mass of reactants that end up as desired product, minimising amount of by-products

  • (Mr of desired product / sum of Mr of all reactants) x 100


for percentage atom economy calculations, use the coefficients


high percentage atom economy =

  • little to no waste product, only the desired product

    • so more economically viable for industrial scale manufacture

  • less mass of reactants that end up as waste

    • so the reaction is more sustainable.

  • less natural resources used

    • so less energy used, so beneficial for the environment


improving percentage atom economy:

  • cannot be improved.

  • sell the by-product to increase profits.


if there is only product in a reaction, the atom economy is 100%



it’s hard to separate 2 solids/liquids/gases produced by a reaction, which makes it difficult to obtain a pure sample






Note
0.0(0)

knowt logo

1.2 amount of substance (notes)


relative atomic mass (Ar)

  • the mean mass of an atom of element, relative to the mass of 1/12th of the mass of an atom of the 12C isotope

average mass of an atom of an element x 12

mass of one atom of 12C

or

∑ (isotope abundance x isotope mass number) x 100

∑ (isotope abundance)


relative molecular mass (Mr)

  • the mean mass of a molecule of a compound relative to 1/12th of the mass of an atom of the 12C isotope


relative formula mass

the sum of the relative atomic masses of the atoms in the chemical formula of a compound

  • ionic compound have a giant ionic lattice with a very large number of ions, so the relative formula mass is the Mr of the empirical/chemical formula


the mole:

  • a unit of measurement that represents a specific quantity of a substance

  • it is the amount of pure substance that contains the same number of particles as there are in exactly 12g of 12C

  • 1 mole of a substance contains 6.022 × 1023 molecules/atoms/ions

    • Avogadro’s constant, L

    • there are 6.022 × 1023 atoms of 12C in 12g of 12C

no. of molecules = nL

n = mass/Mr

n = cv

molarity = moles per dm3 = concentration in moldm-3

molar mass = the mass of one more of a substance = Mr or Ar


gases and volatile liquids follow the ideal gas equation under standard conditions

pV = nRT

p = pressure in Pa

V = volume in m3

m3 ← ÷1000 — dm3 ← ÷1000 — cm3

n = amount in moles

R = ideal gas constant = 8.314 J K-1 mol-1

T = temperature in K

°C —+273 → K

p is proportional to V

V is proportional to T

p and V are inversly proportional

assumptions:

  • gas molecules move randomly

  • there are no forces acting between gas molecules

  • gas molecules are tiny compared to the spaces between them

  • collisions between gas molecules are elastic


1 mole of a gas at room temp = 24 dm3

volume = n x 24 dm3


room temperature = 25°C = 298 K

room pressure = 101 325 Pa ≈ 101 00 Pa = 101k Pa = 1 atmosphere


empirical formula = the simplest whole number ratio of the atoms of each element in a compound

molecular formula = the true number of atoms of each element in a compound

a molecular formula is not practical for giant crystal structures because giant lattices contain a vast number of atoms of each element, and larger crystals will have more atoms than smaler crystals


percentage yield: a measure of the efficient conversion of reactants to products / idea of getting as much product as possible in the reaction

  • (mass of product actually made / maximum theoretical mass of product) x 100

percentage yield may be low if:

  • the product is gas so easily escapes

  • impure reactants are used which cause side products OR not all reactants react (especially in reversible reactions)

  • there are side reactions making other products/there are by-products

  • some of the product is lost during filtration/separation/transferring


atom economy: maximising mass of reactants that end up as desired product, minimising amount of by-products

  • (Mr of desired product / sum of Mr of all reactants) x 100

for percentage atom economy calculations, use the coefficients

high percentage atom economy =

  • little to no waste product, only the desired product

    • so more economically viable for industrial scale manufacture

  • less mass of reactants that end up as waste

    • so the reaction is more sustainable.

  • less natural resources used

    • so less energy used, so beneficial for the environment

improving percentage atom economy:

  • cannot be improved.

  • sell the by-product to increase profits.

if there is only product in a reaction, the atom economy is 100%


it’s hard to separate 2 solids/liquids/gases produced by a reaction, which makes it difficult to obtain a pure sample