6.3 Quantitative Analysis: Titration Flashcards
what is titration
volumetric/quantitative technique to find [unknown] using [known “standard”] in acid-base neutralisation reaction
what is a standard solution
solution with a precisely known concentration
what’s a volumetric flask
measuring flask
what is the analyte
solution in conical flask
what is the aliquot
VOLUME of solution in pipette (into conical flask later)
what is a burette
long glass tube to deliver solutions
how many d.p. can you read off glassware
2 dp
ideal indicators for the titrand
phenolphthalein (basic)
methyl orange (acidic)
what is the titrant
solution added from burette
what is the titrand
leftover titrant
what is the titre
VOLUME of solution added from burette
5 steps: how to prepare standard solution from solids
(1) distilled water on beaker and rod
(2) weigh solid with beaker
(3) dissolve in water using stirring rod
(4) transfer to solution using volumetric flask
(5) add water and shake
rinse all equipment with distilled water to…
get rid of contaminants
pipette and burette are finally rinsed with…
liquid they will contain (base in pipette, acid in burette)
assume …sig figs for pipette and flask
3
how to see colour change in conical flask easier
use white paper underneath
what is a primary standard
solution MADE by dissolving accurate solute in solvent
what is secondary standard
solution whose concentration is determined by titration against a primary standard
hygroscopic solutions…
absorb water
e.g. NaOH, KOH, H2SO4
deliquescent solutions…
so hygroscopic that they dissolve
e.g. NaOH, CaCl2, MgCl2
[X] solutions are not suitable as primary standards because…
deliquescent solutions, because they absorb water and are impure, unstable
efflorescent solutions…
lose water, unstable
e.g. HNaCO3
(can/can’t be used?)
(1) anhydrous substance
(2) hydrated substance
(1) yes
(2) no (unstable)
5 requirements for primary standard
pure, accurately known concentration, stable, high molar mass, reasonably soluble
hydroscopic meaning
absorbs moisture from surroundings = bad as primary standard, unstable
if you dilute a solution by 10x, you must…
multiply the final concentration by 10x
equivalence point vs end point
equivalence = (theoretical) exact stoichiometric ratio for neutralisation to occur
end point = (in practice) when the indicator permanently changes colour
axes of a titration curve
pH against mL of added solution (volume)
where is the equivalence point on a titration curve
midpoint of period of rapid change in pH
indicator used for pH=7
bromothymol blue
indicator used for strong base
phenolphthalein (pH>7)
indicator used for strong acid
methyl orange (pH<7)
(only one/both) solutions must be standard solutions
only one
weak acid or weak base on a titration curve has… (2)
(1) a dip at the start
(2) shorter vertical section
on a titration curve, you can deduce the acid/base pHs by looking at…
the max and min points
equivalence points on a conductivity curve are at…
any apex
how conductivity curves work
there is a measured difference in ionic charges as ions are being replaced in a solution
when do we need back titrations
(1) when it involves solids
(2) or volatile substances (accuracy due to loss of substance)
what are buffers
weak acid and conjugate base OR
weak base and conjugate acid
what buffers do
clean up (neutralise) after added H3O+ or OH- until reaction is neutralised
what’s a buffer region
left region on a titration curve where the pH of a solution remains constant due to the production of a buffer solution
7 strong acids
7 strong bases
sea water buffer system
blood buffer system
Mohr’s method of back titration
