Volumetric analysis Flashcards
Quantitative analysis
finding the quantities or amounts of material present
volumetric analysis
involves reacting volumes of solutions with eachother
what is a solution
mixture of a solute and a solvent
homogenous
when the particles of a solute are uniformly distributed throughout the solvent
concentrated
large amount of solute to solvent
dilute
small amount of solute to solvent
concentration
the amount of solute thats dissolved in a given volume of solution
what are the three ways to express concentration of a solution?
percentage of solute
parts per million
moles of solute per litre of solution
what are the three ways to express somthing by percentage of solute?
weight per weight
weight per volume
volume per volume
what is w/w
weight by weight
-g per 100g of solution
what is w/v
weight by volume -g per 100cm3 of solution
what is v/v
volume per volume#
cm3 per 100g of solution
what is ppm and what is it used for
parts per million, used for very diluted solutions
1mg / L
what is number of moles of solute for litre of solution
number of moles per litre of solution
What is the essential equiptment used for volumetric analysis
volumetric flask
why do chemists use standard solutions
they often use solutions of known concentration to figure out the concentration of another solution of an unknown conc
what is a standard solution
a solution whos conc is accurately known
how is a standard solution prepared
its prepared by dissolving a definite, percesily known mass of solute in a suitable solvent to give a definite precisly known volume of solution
primary standard
a substance that can be obtained in a stable,pure and soluble soild form so that it can be weighed out and dissolved in water to give a solution of accurately known conc
samples of primary standard
anhydrous sodium carbonate
sodium chloride
potassium dichromate
Describe how you would prepare a standard solution of sodium carbonate
- use a balance to measure out the pure anhydrous sodium carbonate on a clock glass
- transfer sodium carbonate to clean beaker, dissolve with DI water.
- mix until fully dissolved, wash down everything with DI water.
- pour into funnel into volumetric flask, collecting rinsingles.
- filll the flask with Di water until around 1cm of the callibration mark
- view at eyelevel and fill slowly until bottom of the menucus rests on the callibration mark
- stopper the flask and invert it several times to ensure a homoengeous solition
Why is it possible to make up a standard solution of sodium carbonate directly?
Because Na2CO3 is a primary standard, i.e. very pure and stable.
What precaution is taken to ensure that all of the sodium carbonate is transferred from the clock glass to the beaker?
the clock glass is rinsed with DI water, these rinslings are transferred to the beaker
why is a stirring rod used
speed up the dissolving of sodium carbonate- prevent formation of hard lumps of the sunstance
Why is it necessary to wash the solution off the stirring rod into the beaker?
To ensure that none of the sodium carbonate solution is lost
Why are the rinsings from the beaker added to the volumetric flask?
To ensure that all of the sodium carbonate solution is transferred to the volumetric flask.
Why is it necessary to be particularly careful when adding the last few drops of water to the volumetric flask?
there is danger of overshooting the mark,resulting in a solution of an unknown conc, then you will have to start again
When the solution has been made up, why is it necessary to mix the contents of the
flask thoroughly? What feature of the volumetric flask makes this particularly necessary?
to ensure a homogenous solution, narrow neck of the slask
Why is a beaker, rather than a conical flask, used when the solute is being dissolved?
sprout facilitates pouring- stirring is easier because it has a wide neck
why is a funnel used
minimise the risk of spillage
why is Na2CO3 added slowly, with stirring, to the beaker
to prevent the formation of hard lumps of sodium carbonate that are hard to dissolve.
what is the concentration of a solution dertimined by
its dertimined by reacting that solution with another solution of a known concentration ( primary standerd or secondary standard)
what is the end point / equivalence point
the point at which the two solutions have reacted completely
the conc of a solution is recorded by..
the volumes of the two solutions at end point
Role of a graduated cylinder
measured volume, isnt accurate due to wide neck
Role of volumetric flask
contains a definite amount of a solution.
callibration markto ensure solution is accurate.
mix via inverting (homogenous mixture)
base of meniscus rests on mark
Role of pipette
designed to draw up a percise amount of solution 25 cm3 usually
Role of burette
fill above mark and open to ensure bottom is filled w/liquod, no air bubbles.
shows volume decreasing downwards
Role of conical flask
shape suitable for swirling.
place white tile underneath to see colour change clearly
Role of pestle + mortar
used to break down any solid into smaller pieces so that it can be easilty dissolved in a solution
What is the indicator used?
What are its colour changed
To use the standard solution of sodium carbonate to standardise HCl
methyl orange
yellow to pink
Describe using the standard solution of sodium carbonate to standardise HCl
- pour HCl solution into a beaker
- rinse out burette and prepare it
- rinse out burette with HCl then fill with HCl above the zero mark.allow to flow until @ zero
- use white tile to see colour change, record liquid
- rinse out pipette with DI water and Na2CO3 into clean concial flask
- add methyl orange indicator- note colour
- carry out a rough titration- note burette reading
- pipette Na2Co3 into flask
- repeat titrations for more accurate reading - within 1 cm3
- stop when definiate colour change
- calculate the conc of HCl
describe the apperange of sodium carbonate
white solid
why must the mass of sodium carbonate dissolved in the water be known accurately
so that the conc of the NaCo3 can be calculated accurately
why is Na2Co3 a primary standared?
it can be obtained in a pure and stable form
state two benefits of a volumetric flask for making up the solution
the volume of the solutio is accurately known
the design of the solution allows it to be shaken easily to ensure a homogenous solution
why is it not recommended to pipette directly from the volumetric flask
rick for glass breakage
why is it important not to add too much indicator
indicators are either weak acids or weak bases- too much could effect the accuracy of the result.Too much indicator could give a very intense colour that may make itto see the colour change at the end point
why do we have to standardise HCl solution
To use the standard solution of sodium carbonate to standardise HCl
HCl is not a primary standard
why carry the expeirment out more than once
more accurate titration figure - average of two readings aggreing withing 0.1 cm3 is used
apperance of isolated sodium carbonate
white crystalline solid
name the indicator used and its colour change
make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample
methly orange
yellow to pink
to find the end point accuratly
make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample
- rinse burette,pipette…
- using pipette,transfer NaOH into conical flask, add indicator.
- fill burette with HCl
To obtain a sample of salt
make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample
add NaOH to beaker,just enough HCl to netralise it (NO INDICATOR)
gently heat the solution until all the water has evaporated to dry-ness.
sodium chloride will remain in its beaker
another suitable indicator for this reaction?
make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample
methyl red/ phenolphthalein
why is it undesirable to put sodium hydroxide solution into the beaker rather than the conical flask
make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample
if the burette is notwashed out propally after use, sodium hydroxide may crystallise in the teflon tap-causing blackage of the burette nozzle or changing the conc of a diluted solution
what indicator is used and what colour does it change
Dertermination of the concentration of thanoic acid in vinegar
phenolphtalein
pink to colourless
describe how to dertimine the concentration of thanoic acid in vinegar
- dilute vinegar with water to callibration mark of a volumatric flask.
- rinse out pipette and burette with their respective solution
- place NaOH into conical flask with a couple drops of phenophatlein indicator
- fill burette with vinegar
- carry out titration
- calculate conc of thanoic avid in diluted vinegar solution
Why is the vinegar diluted
Dertermination of the concentration of thanoic acid in vinegar
avoid a very small titre,which would reduce the accuracy of the expeirment.
also reduces the amount of vinegar and NaOH needed
what is the Indicator used, describe its colour
Dertimination of the amount of water crystallisation in hydrated sodium carbinate
methyl orange
yellow to pink
Method of dertermining of the amount of water crystallisation in hydrated sodium carbinate
- weigh the hydrated sodium carbonate correctly, dissolve in DI water
- transfer to volumetric flask
- …
- titrate the Na2CO3 solution against HCl
- repreat until the readings agree within 0.1cm3
- calculate the conc of hydrated sodium carbonate
What was done to the volumetric flask and its contents immediately after the
solution had been made up to the mark with deionised water? Why was it important
to do this?
It was stoppered, and then inverted several times. To ensure a homogeneous solution.
Describe the physical appearance of hydrated sodium carbonate
White crystalline solid. However, if larger crystals are purchased, these tend to
have a clear glassy appearance.
Explain water of crystallisation.
Water chemically bound in the compound, which gives rise to the crystalline form or water
present in definite proportions in crystalline compounds.
Name another compound that has water of crystallisation present.
Hydrated copper sulfate
