Amount of substance (Physical Chem)

define relative molecular mass

• The relative molecular mass of a molecule is the ratio of the average mass of that

  molecule to 1/12th of the mass of an atom of carbon-12.

define relative atomic mass

• The relative atomic mass of an atom is the ratio of the average mass of one atom of that

  element to 1/12th of the mass of one atom of carbon-12.

define molar mass

• mass of 1 mole of atoms, molecules or formula units

• e.g molar mass of chlorine is 35.5 so, 35.5g of chlorine contains 1 mole, or 6.02 x 10^23 of chlorine atoms

• units = g/mol

how to find the molar mass of a compound

• work out the relative molecular mass

how to work out moles - 2 ways

• mass(g) / relative molecular mass

• number of particles / avogadro constant

formula for concentration

moles (amount of solute) / volume(solution) (dm³)

mass(g) / volume (dm³)

go from mol/dm³ to g/dm³

mol/dm³ x Mr

1dm ³ = ?

• 1dm³ = 1000 cm ³

• 1cm³ = 0.001dm³

• 1dm = 10cm

what does avogardro’s laws state?

Avogadro's law states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Q: At RTP, what volume does 1 mole of any gas occupy, and what equation can be used to calculate the

volume of a gas?

1 mole = 24 dm³ at RTP (298 K and 100 kРа).

Volume of gas (dm³) = moles × 24

Q: What temperature in Kelvin is equal to 0°C?

A: 273 K.

what does the ideal gas equation allow us to do?

It allows us to find the number of moles of gas molecules in certain volume at any temperature and pressure.

what is the ideal gas equation

pV = nRT

pressure x volume = moles x molar gas constant x temperature

P = pressure

V = volume

N = amount in moles

R = molar gas constant (8.31 J K^-1 mol^-1)

T = temperature in K (°C + 273 = K)

how to go from degrees celsius to to kelvin

add 273

when does The ideal gas equation work best

Pressure is not too high

Temperature is not too low

Gas molecules are not too large

Equation is less reliable if gas is close to liquefying.

Q: What are the conversions between m³, dm³ and cm³?

1m³ = 1000dm³ = 1000000cm³

define empirical formula

simplest whole number ratio of elements in a compound

how does empirical formula vary from ionic, macromolecular compounds and molecues

ionic and macromolecular compounds = same actual formula

molecules = could be different or not

define molecular formula

• A molecular formula is the actual number of atoms of each element in the compound.

• simple multiple of the empirical formula

define a mole

The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.

formula for percentage yield?

formula for percentage atom economy

what are the 3 reasons the actual yield might be smaller than the theoretical yield

• side reactions / reversible reactions

• impure reactants

• loss to vessels on transfer

what is percentage yield?

percentage yield is the percentage of the theoretical yield obtained

what is percentage atom economy

theoretical percentage measure of the amount of starting materials that ends up as the desired products.

the higher the percentage atom economy, the less waste is produced, and the more efficient the reaction.

a reaction with high percentage yield but low atom economy will?

produce more desired product but more waste product too.

simple rules to remember the solubility of some common ionic compounds

describe neutralisation reactions

involve reactions of acids with metals and bases

solutions of ions react and form covalent compounds

what are acids

proton (H+) donors, and produce H_⁺ ions when in an aqueous solution

describe the type of acids

strong acids are fully dissociated in solution

weak acids are only partially dissociated in solution

what are bases and describe the types

• proton acceptors

• metal oxides, metal hydroxides, metal carbonates and ammonia

• soluble bases known as alkalis

• produce hydroxide ions (OH-) in aqueous solution

strong bases are fully dissociated in solution

weak bases are only partially dissociated in solution

complete them?

what is titration and what is it used for

• method of volumetric analysis

• it is typically used to find the concentration of an acid or alkali

• they can also be used in redox reactions

in titrations what is usually titred against the solution of unknown concentration

standard solution

basic method of titration

describe the different indicators used in acid - base titrations