LEC 6B

the biggest mistake you can make raw is being afraid to make one

sino dito ang takot magkamali?

ME šŸ¤“šŸ‘†

pag takot ka magkamali competitive ka raw e putangina pabagsak na nga di na pwede magkamali !

ā€œdid you do your best?ā€

GEROA LEORA

factors to consider when performing redox titration

  • ph

  • oxidation state

  • keep in mind this is still titration

  • titration - relating one substance to another using volume na nagamit sa titration

  • sa oxidation number nagkakaroon ng changes kaya tinawag na redox titration

  • calculations are the same

  • back titration tatanggalin lang yung excess then relate sa analyte

slide 2

elo

  • not much difference w respect to other types of titrations

  • pinagkaiba lang is the change in oxidation number

  • still relating one substance to another

  • the reason why we are adjusting oxidation states is because we want only one oxidation state of the substance na tina-titrate

slide 3-8

general principles of redox titrations

  • iisa lang ang oxidation state, if not, mahihirapan i-relate stoichiometrically

  • quantitative - defined chemical reaction

  • if di mabilis ang reaction, we do indirect or back titration

  • indicators - they all change in color kapag may excess na sa isa sa mga products or reactants

  • self-indicators - potassium permanganate (purple) if di pa excess, colorless

  • potentiometric method - require the use of ph meter; change in ph

  • basta indicator kaya mag-indicate ay malamang

slide 9-11

preadjustment of oxidation state

  • purpose is to make our reactants/titrant/analyte to be present in just one oxidation state YUN LANG YON dami ebas sa ppt

  • auxiliary reducing agents can be directly placed in the solution

  • auxiliary reducing agentā€™s goal is to reduce everything

  • question: paano malalaman if everything is reduced?

  • example: naglagay ng al or zn pero may natira pa na nirereduce sa sample, paano malalaman if okay na? alin ang dapat excess, solution or metal? the solution contains the analyte, metal nagree-reduce. dapat excess ang metal.

  • pwedeng ma-solve backwards esp if you know the concentration of the titrant

  • reductors - to reduce

slide 10-14

jones reductor ZINC A. JONES

  • a for amalgamated

  • contains mercury and zinc

  • crucial: formation of electrons

  • kailangan ni zinc solid hinalo sa mercury para maging zinc2+ (nag-release ng 2 electrons, and yung 2 electrons yung magpapareduce)

walden reductor SILVER G. WALDEN

  • g for granular

  • same same except silver lang gamit

slide 15-17

auxiliary oxidizing agents

  • their goal is to oxidize

  • electrons are on the reactant side now

  • siya yung tatanggap ng electron para makapag-oxidize

  • ammonium peroxydisulfate

  • hydrogen peroxide

  • sodium bismuthate

  • + e naught - sponti

  • the change in oxidation number happens bc of electrons either binibigay or inaabsorb ng either reducing or oxidizing agents

slide 21

starch-iodine complex

  • starch indicator ng iodine

  • dark blue or black blue color pag nag-react si starch kay iodine

  • iodometry kadalasang ginagamit sa treatment ng dissolved oxygen

  • and treatment ng dissolved oxygen ginagamit sa treatment ng water

slide 22-23

stability of sodium disulfate

  • reducing agent or titrant yan

  • always standardize titrants

  • kaya standard soln kasi yun yung basehan kung ilan yung analyte sa unknown sample

slide 25

permanganometry

  • potassium permanganate

  • self-indicator

  • electrons in the reactant

  • advantages: without the use of indicator*

  • disadvantages: need ng primary standard, reaction w chloride means may kaagaw si chloride kaya di na pwede i-relate

cerimetry

  • nareduce from +4 to +3

  • cerium ang ginagamit hence the name

  • indicator: ferroin (if may indicator na ginagamit, hindi ganun ka-distinct yung color change ng yellow to colorless)

dichrometry

  • dichromate ginagamit titrant

  • orange to green

  • advantages: di na need ng primary standard (should be present in high purity), analyte lang dapat reactant ni dichromate,

  • disadvantages: requires back titration

iodometry

  • needs primary standard

  • indicator: starch

  • pag mababa dissolved oxygen, onti oxygen sa water

  • winkler method - used to check the dissolved oxygen; determine the dissolved oxygen sa freshwater systems

bromatometry

  • titrant: potassium bromate ā€˜

  • indicator: methyl orange (irreversible) red to colorless

  • p-ethoxy chrysoidine (reversible) - a derivative of CG red to orange

summary

  • 5 redox titrations

  • pinagkaiba lang ay mga titrants but the process of computations are the same

  • need lang malaman reaction, saan related si analyte sa reaction

  • sample has to be buffered (usually to an acidic ph)

  • bufferā€™s purpose para walang abrupt change, as much as possible for the whole process of titration, nasa certain ph range lang