Titrations

What is a titration

an analytical technique that involves acid base reaction, used to find concentration of an unknown

What is a primary standard solution

solution with known concentration used to find concentration of unknown

what is the equivalence point

Theoretical point in titrations, where stoichiometirc amounts of acid and base has reacted ( nothing is in excess/ reaction complete).

what is end point

when indicator changes colour, signaling equivalence point has been reached

What are the properties of a primary standard

• have high molar mass

• available in pure form

• have high solubility

• goes through known reactions

• doesnt react with CO2 in atmosphere

• doesnt absorb/ dissolve in water ( isnt deliquescent)

• doesnt absorb moisture in air ( isnt hygroscopic)

why is NaOH a bad primary standard

• doesnt have a high molar mass

• is hygroscopic and absorbs CO2 in air

• mass varies over time

• isnt pure

what is the pipette rinsed with in titration set up

small amount of solution going into flask

what is the flasks rinsed out with in titration set up

distilled water

how do you find titre

final reading - intital reading

what is the precision margin ( difference between 2 values) in titration

±0.10 mL difference between values next to each other

how is % purity found

m ( pure) / m ( impure) X 100

how do you find concentration of undiluted solution

C1V1= C2V2 or C1V1/V2 = C2

how many equivalence points/ steeps does polyprotic acids have

mulitple equivalence points related to number of hydrogens they can let go of

where is the equivalence point of a titration curve

on the steep line, where it is vertically straight ( middle point normaly)

what indicator is best for when equivalence point is basic

phenolphthalein

what indicator is best for when equivalence point is acidic

Methyl orange

what is the pH of strong acid + strong base and why

pH=7 ions produced dont go through hydrolysis as the ions are neutral

why doesnt weak acid + weak base go through hydrolysis

ions produced are neutral

what are neutral ions/ salts

conjugate base of strong acid, Positive ions from Group 1 & 2, salts formed by the reaction of a strong acid with a strong base

what are the marks for answering why indicator selection

• state chosen indicator

• state ion that will go through hydrolysis

• write equation for hydrolysis

• say “ solution will have ( acidic/basic) equivalence point due to excess ( OH- or H3O+)

• “ pH at which end point occur at/ colour changes approximated pH of equivalence point”

what colour changes to

what is the pH region for strong acid + weak base

acidic equivalence point as ion produced goes through hydrolysis and products are CB and H3O+ ions

what is the pH region for weak acid + strong base

basic equivalence point as ion produced goes through hydrolysis and products are CA + OH- ions