redox titrations Flashcards
what is an alkali
a base that releases hydroxide ions in aqueous solution
what 2 approximations are made when calculating PH of a weak acid
that the H+ conc is equal to A- conc
the HA at equilibrium is equal to the initial conc.
what is the initial colour change when thiosulfate-iodine titration is carried out?
Orange fades to yellow as iodine is used up.
what colour change do you look for when adding manganate solution.
colourless changes to permanent pink
what does a big pKa mean
the acid is weak
what does a big Ka mean
the acid is strong as the acid dissociation lies closer to the right
what is a salt bridge
concentrated solution of an electrolyte soaked into filter paper to connect two half-cells
what does an oxidising agent do
takes electrons from the species that is oxidised
when does the approximation H+= A- for a weak acid breakdown
very dilute solutions or weak acids the H+ from the water dissociation is significant compared with the H+ from the acid
when should you add the iodine in an iodine-thiosulfate titration
only when faded to pale yellow
what colour is phenolphthalein in acid and in alkali
colourless in acid
pink in alkali
what does a fuel cell do
uses energy from the reaction of a fuel with oxygen to create a voltage
define a base
a substance that reacts with an acid to make a salt
what does a reducing agent do
it donates a pair of electrons to the species that is being reduced
what is the difference when reading the burette scale with a manganate titration
read from the top of the meniscus because its dark purple you cant see the bottom of the meniscus
when does the approximation that HA at equm =initial HA not work
when the weak acid is still quite strong as quite a lot of the HA will dissociate so this isn’t true
give 2 limitations of predictions of feasibility using electrode potentials
reactions may have too high an activation energy so the reaction may not take place.
the reaction may not take place with 1moldm-3
what is the name of the species made when H+ dissolves in water
hydronium ion, H3O+
Kw chnages with temperature. will the PH of water be 7 at all temperatures
NO
What is the Kw expression
Kw= [H+][OH-]
if a standard electrode potential is very negative, what does this tell us for the likelihood og gaining/losing electrons
likely to lose electrons/ be oxidised
write the Ka expression for a weak acid
Ka= [H+][A-]
[HA]
what indicator is used at the end of a iodine-thiosulfate titration
starch solution
what is the name of Kw
ionic product of water
