chem tricky bits

• rate equation:

  rate = k [reactant 1] [reactant 2]

  the orders of the reactants are the powers of the reactants
• rate-determining step: the slowest step in a multistep reaction
• the rate equation of a reaction will be derived from the rate-determining step
• can find the rate determining step from the rate equation by finding which step has the same ratio of reactants as the rate equation
• complex ion: a molecule with a transition metal ion in the middle with ligands coordinately bonded to them
• ligand: an atom, ion, or molecule that donates a pair of electrons to a central metal ion
• coordination number: a number of coordinate bonds surrounding the metal ion
• monodentate ligands: only donate one lone pair of electrons to metal ion
• bidentate ligands: donate 2 lone pairs of electrons to metal ion (bonds twice to metal ion)
• polydentate ligands: donates multiple lone pairs of electrons to metal ions (bonds multiple times to metal ion)
• coordination number 6

  • octahedral shape
  • bond angle: 90 degrees
• coordination number= 4

  • tetrahedral, bond angle 109.5
  • square planar, bond angle 90
• naming coordination compounds

  1. oxidation state of metal
  2. name the cation
  3. name anion
• testing for cations

  • flame test
  • sodium hydroxide test
  • test for ammonium ions
• flame test

  • lithium + = crimson
  • copper 2+ = green
  • potassium + = lilac
  • sodium + = yellow
• sodium hydroxide test

  • copper 2+ = blue precipitate
  • iron 2+ = green precipitate
  • iron 3+ = brown precipitate
  • aluminum 3+ = white precipitate, dissolves in excess NaOH
  • magnesium 2+ = white precipitate
• testing for ammonium ions

  • add NaOH then heat
  • damp red litmus paper goes blue
• testing for anions

  • halide silver nitrate test
  • testing for carbonates
  • testing for sulfates
  • testing for nitrate ions
• halides silver nitrate test (AgNO3)

  • chloride - white, dissolves in dilute ammonia
  • bromide - cream, dissolves in concentrated ammonia
  • iodide - yellow, insoluble in ammonia
• testing for carbonates

  • react CO3 2- with acids
  • test for carbon dioxide release with lime water
• testing for sulfates

  • barium chloride test
  • produces white precipitate if positive
• testing fro nitrate ions

  • add devorda's alloy and sodium hydroxide
  • damp red litmus paper goes blue
• anode - positive electrode where oxidation takes place
• cathode - negative electrode where reduction takes place
• electrolyte: the substance that is broken down in electrolysis
• rules at electrolysis anodes

  • oxygen gas is produced unless halide present
  • 4 hydroxide ions (- charge) --> oxygen + 2water + 4 electrons
• rules at electrolysis cathodes

  • hydrogen produced unless the metal is copper, silver, or gold
  • proton (H+) + electron --> H
• electrode potentials

  • tell us how readily a chemical substance gains electrons
  • the more positive the electrode potential, the greater the tendency to gain electrons
• standard electrode potential definition

  • the e.m.f of a hald-cell measured against the standard hydrogen electrode under standard conditions of 298K, 1 moldm-3, 100kPa
• the more positive standard electrode potential will have a forward reaction
• the more negative standard electrode potential will have a reverse reactions
• cell potential = most positive electrode - least positive electrode
• • electrons flow away from least positive half-cell to the most positive half cell
  • most positive half cell is the positive electrode (anode)
  • least positive half cell is the negative electrode (cathode)
• greenhouse effect

  1. solar energy reaching earth mainly as visible + UV
  2. earth absorbing some of this energy, heating up and radiating IR
  3. greenhouse gases in troposphere absorbing some of this IR in the IR window
  4. absorption of IR by greenhouse gas molecules increases vibration energy of their bonds, energy is transferred to other molecules by collisions, increasing their kinetic energy + raising temperature
  5. greenhouse gas molecules re-emit some of absorbed IR in all directions, some heats up earth
  6. increased concs of greenhouse gases leads to enhanced greenhouse effect
• general formula of group 2 carbonates: MCO3 (M = metal)
• thermal decomposition of group 2 carbonates:

  MCO3 --> MO + CO2

  metal carbonate --> metal oxide + carbon dioxide
• group 2 trend in thermal stability:

  • going down the group, resistance to thermal decomposition (thermal stability) increases
• reason for group 2 metal carbonate trend in thermal stability

  • carbonate ion has a large electron cloud that can be distorted when near positive group 2 metal ions
  • all group 2 metal ions have 2+ charge but they become larger as go down group, meaning charge is spread out over larger area (lower charge density)
  • lower charge density = less distortion the metal ion has on the carbonate ion
  • less distortion = the more stable the carbonate ion is = higher thermal stability
• acid hydrolysis of esters

  • using dilute acid to split an ester into a carboxylic acid and an alcohol
  • use sulfuric of hydrochloric acid
  • conducted under reflux
• base hydrolysis of esters

  • using a dilute base to split an ester into a carboxylate ion and a alcohol
  • use sodium hydroxide
  • conducted under reflux