Volumetric analysis - Pari is desperate

indicator for: standardizing HCL using anhydrous sodium carbonate

• methyl orange

• yellow (base) to pink (acid

methyl orange colour change

yellow in bases, pink in acids

Q: Explain why a standard solution can be directly made up from anhydrous sodium

carbonate

it is a primary standard solution

Explain why a standard solution of hydrochloric acid CANNOT be directly made up i.e.

why must hydrochloric acid be standardised by titration?

HCL is NOT primary standard

indicator for previously standardized HCL being used to standardise sodium hydroxide

methyl orange

phenolphthallein colour change

pink in bases, colourless in acids

indicator for previously standardized HCL to standardize ammonia

methly orange

indicator for sodium hydroxide standardizing ethanoic acid in vinegar

phenolphthalein (weak acid, strong base)

Why was the vinegar diluted before being used in a titration?

The vinegar is diluted so that a larger volume is required to reach the endpoint. This

gives a larger titre value and reduces the percentage error

whats a standard solution

solution whose concentration is accurately known

what is meant by a primay standard

substance which is pure, stable in air, has a high mr and can dissolve easily in water to directly make a standard solution

what standard is anhydrous sodium carbonate

primary

equivalance point

point where two solutions JUST react completely with eachother - end point

titration

procedure where the measured volume of one solution is added to a known volume of another solution until the reaction is complete

analyte

species being analysed

solution

perfect, homogenous mixture of solute and solvent

secondary standard

not available in 100% purity, not stable in air, low molar mass, not easily soluable in water and not easily made up to a standard solution

why is sodium hydroxide a secondary standard

deliquescent

why is potassium manganate 7 a secondary standard

decomposes in strong sunlight, not available in pure state and does not easily dissociate in water

why is iodine secondary standard

undergoes sublimation

why is soidum thiosulphate secondary standard

not available in 100% purity

why are only a few drops of indicator used in titration

indicators are themselves either weak acids or bases, and will take part in the reaction. Few drop sto minimise their taking part

formula for volumetric analysis

VaMa/Na = VbMb/Na

1ppm =

1mg/L

%w/w

grams per 100g

%v/v

cm3 per 100cm

%w/v

grams in 100