define relative atomic mass
Ar, ratio of weighted average mass of 1 element atom:1/12 mass of 12C atom
define isotopic mass
ratio of mass of 1 element isotope atom:1/12 mass of 12C atom
define molecular mass
(Mr)of covalent compound; ratio of weighted average mass of 1 substance molecule:1/12 mass of 12C atom
define formula mass
(Mr)of ionic compound; ratio of weighted average mass of 1 formula unit:1/12 mass of 12C atom
define mole
unit of measurement, measures amount of substance in given mass/volume >
1 mole of substance = amount of substance containing 6x1023(Avogadro's constant) particles
calculate Ar of element given relative abundances of isotopes
Sum of (% of isotope x isotope mass) = weighted average
define empirical formula
formula showing simplest whole no. ratio of atoms of diff elements in compound
define molecular formula
formula showing actual no. of atoms of diff elements in 1 molecule of compound
calculate empirical formula by combustion data
hydrocarbon combustion general equation
CxHy(g) + (x+y/4)O2(g) -> xCO2(g) + (y/2)H2O(l)
given organic compound mass, CO2,H2O mass,
all C converted to CO2, all H converted to H2O;
calculate nCO2 to get nC, then mass of C >
calculate nH2O to get nH, then mass of H >
calculate simplest mole ratio
calculate empirical formula by using volume of gases in combustion reactions
hydrocarbon combustion general equation
CxHy(g) + (x+y/4)O2(g) -> xCO2(g) + (y/2)H2O(l)
volume ratio=mole ratio,
all hydrocarbons burn in excess O2, give H2O, CO2 as only pdt;
after complete combustion,
1st contraction in gases vol when mixture cooled to rtp >
2nd contraction in gases vol when mixture passed thru base, acidic CO2 reacted away >
1st contraction = total initial vol - total final vol = V(CxHy) + V(O2 reacted) - V(CO2)
2nd contraction = V(CO2)
determine percentage yield of product
theoretical yield; max calculated pdt quantity when all LR reacted
actual yield; pdt quantity actually obtained during experiment
% yield = actual yield/theoretical yield x 100%
how to balance redox equations
no. of e- lost from RA = no. of e- gained by OA
disproportionation rxn; redox rxn, same species simultaneously [R] & [O] >
KOHe(acidic medium)
balance Key element
balance O2 by adding H2O
balance H by adding H+
balance total charge by adding e-
if basic medium, add same no. of OH- as H+, give H2O
how to calculate new oxidation no. of element
when known nA react w/ stoichometric nB, can calculate change in O.S;
construct half-eqn for A(initial, final O.S known) >
calculate n(e- lost/gained) using nA; equate amount to n(e- gained/lost) by B >
determine no. of e- transferred by 1 mole of B using mole ratio >
determine new oxidation no. of B