S1.4 Counting Particles; moles

S1.4.1 Avogadro & masses

6.02×10²³ = N_A

A carbon-12 atom has 1.99×10^-23 g = small, so need units to make easier… 12g of C-12 = 6.02×10²³ molecules.

A_r = relative atomic mass; weighted average of 1 atom compared to 1/12 mass of a C-12 atom. - unitless
M_r = relative formula mass: same calculation as above but for molecules

N_A×n = N (n = moles)(Nr of particles)

M = molar mass: mass of 1 mole of substance: g mol^-1

m (total mass) = n×M

S1.4.2 Emperical/Molecular formula

Empirical shows the rations, molecular the actual amounts. Use percentage compositions to see these ratios, then use molar mass to see how maaany empirical fit into molecular to find formula.

CH₂O → C₆H₁₂O₆

S1.4.3 Concentrations of solution

c = ⁿ/_V, V= ⁿ/_c, n = cV. Volume=dm³, c = moldm^-3.
cm³ → dm³ = /1000.

Can have concentrated dilute blablabla. can measure in parts/million, mass/dm3 etc, but we use moles/dm3.

S1.4.4 Gas baaaasics

Equal volume of contain same nr of molecules under STP.
Molar volume - 22.7 mol dm^-3
STP = 0^oC (273K), 100kPa

Unbalanced reactions; limiting is the one where theres too little, excess is too much…