Stoichiometry
Topic 1
Mole calculations:
States of matter:
Solid: fixed shape & volume
Liquid: fixed volume, no fixed shape, particles can flow over each other
Gas: no fixed volume & shape, particles can flow over each other
Boiling point/ melting point:
Pure substances: sharp MP & BP
With impurities: BP increases, MP decreases
Changes in state:
(physical change)
Elements:
Simplest form of matter
Cannot be broken down or separated into a simpler
form by chemical means
Building blocks for all other substances
Found on the periodic table
Some elements exist as diatomic (O2)
Compounds:
Chemical combinations of 2 or more elements in
fixed ratio
Cannot be physically separated
Have properties different from the one combined
Mixture:
Contains one or more element or compound that are
not chemically combined
Homogeneous mixture has a constant composition
throughout.
Heterogeneous mixture have visibly different
substances or phases.
Relative atomic mass (Ar): average mass of an
atom relative to 1/12 mass of a C-12, taking into
account of its abundance
Relative molecular mass (Mr): sum of all atomic
masses of elements in a compound
Moles: 12g of C-12 = 1 mole = 6.02 x 1023 particles
(Avogadro’s constant)
Empirical formula: simplest whole number ratio of
atoms a compound contains
Molar mass: mass of a mole of a species (g/mol) addition of the Ar of individual atoms
Molecular formula: multiple of simplest whole
number ratio - show the actual number of atoms in 1
mole of compound
Theoretical yield (Ty): maximum amount of product
that can be produced
Limiting reactant: used up completely in a reaction
& will limit the reaction
Experimental yield (Ey): measured amount of
product obtained from the reaction/ through an
experiment
Excess reactant: do not get used up completely in a
reaction
Percentage yield: (Ey/ Ty) x 100
Avogadro’s law:
- Equal volume of different gases contain equal number of particles at the same temperature & pressure
- Volume is directly proportional to number of moles of gas
Ideal gas:
- No attractive forces between molecules
- Has negligible volume
- No energy loss during collisions (elastic collisions)
Ideal gas law: PV = nRT
- P: pressure in Pa
- V: volume of gas in m3
- n: number of moles
- T: temperature in Kelvin
- R: ideal gas constant (8.31 JK-1mol-1)
Molar mass of gas:
- M = (dRT)/P
- M = (mRT)/ (VP)
- d: density
Measurement & data
processing
Topic 11
Types of Error
Absolute; raw precision of equipment.
Fractional error; absolute error/measured value.
Percentage error; fractional error in percentage.
Calculating Uncertainty
Adding/subtracting values, add the absolute error together
Multiplying/dividing values, add the fractional error together.
The final uncertainty is expressed in absolute error.
10 ± 0.5 cm; 0.5/10 = 0.05
Addition/subtraction, round the value off to the fewest decimal places.
Multiplying/dividing, round the value off to the fewest significant figures.
Acid & bases
Topic 8
Brønsted-Lowry acids & bases and their reactions
Brønsted-Lowry Acid
-
A substance which donate a proton or a H+ to
other compounds
Example: HCl(aq)+ H2O(l) ⇌ H3O+(aq)+ Cl-(aq)
-
HCl donates H+ to H2O, hence it is a
Brønsted-Lowry acid
Brønsted-Lowry Base
-
A substance which accept a proton or a H+ to
other compounds
Example: B(aq)+ H2O(l) ⇌ HB+(aq)+ OH-(aq)
-
B accepts H+ from H2O, hence it is a
Brønsted-Lowry base
Acid reaction
-
Metal → salt + H2
Metal oxide / hydroxide → salt +
H2O
Metal carbonate / hydrogen
carbonate → salt + H2O + CO2
Ammonia → ammonium salt
Conjugate Pairs
-
Every Brønsted-Lowry acid-base
reaction has 2 conjugate acid-base
pairs
Base reaction
-
Acid → salt + H2O
H2O → hydroxide ions
Amphiprotic Series
-
-
The substance that can be both
Brønsted-Lowry acid or base
depending on the reaction
They can both donate or accept a
proton or H+ ions in a reaction
Example: Polyprotic series, Amino acid, Water
IMPORTANT!! Amphiprotic substances are amphoteric, but amphoteric substances without a proton or H+ ions are not amphiprotic
pH
pH = -log10 [H]
Ka
Low Ka= weak acid
[H]=10^pH
= Kc for weak acid/ base dissociation
Low kPa= strong acid
Kw
E.g. CH3COOH <-> CH3COO + H
= ionic product constant
Ka= [CH3COO][H]/[CH3COOH]
= [H][OH]
pKa
= 1 x 10^-14
= dunno for wud use, just to make our
life harder
= -log10Ka
Acid Rain
Normal Rainwater has a pH around 5.0 to 5.6.
Acid rain is when the pH of the water is lower than 5.0, making it acidic and
corrosive when reacted with marble and limestone.
Acid rain is formed when normal rainwater reacts with
carbon dioxide, nitrogen oxide and sulfur dioxide.
CaCO3 + 2HNO3 -> Ca(NO3)2 + H2O + CO2
S + O2 -> SO2
CaCO3 + H2SO4 -> CaSO4 + H2O + CO2
H2O + SO2 -> H2SO3 sulphurous acid
2SO2 + O2 -> 2SO3
SO3 + H2O -> H2SO4 sulphuric acid
2N + O2 -> 2NO
4NO + H2O + O2 -> 4HNO3 nitric acid
2NO + O2 -> 2NO2
4NO2 + 2H2O + O2 -> 4HNO3 nitrous acid
2NO2 + H2O -> HNO3 + HNO2