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 of solutions

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

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

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)

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

simple multiple of the empirical formula