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Chemistry > Volumetric analysis > Flashcards

Volumetric analysis Flashcards

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1
Q

Quantitative analysis

A

finding the quantities or amounts of material present

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2
Q

volumetric analysis

A

involves reacting volumes of solutions with eachother

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3
Q

what is a solution

A

mixture of a solute and a solvent

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4
Q

homogenous

A

when the particles of a solute are uniformly distributed throughout the solvent

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5
Q

concentrated

A

large amount of solute to solvent

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6
Q

dilute

A

small amount of solute to solvent

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7
Q

concentration

A

the amount of solute thats dissolved in a given volume of solution

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8
Q

what are the three ways to express concentration of a solution?

A

percentage of solute
parts per million
moles of solute per litre of solution

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9
Q

what are the three ways to express somthing by percentage of solute?

A

weight per weight
weight per volume
volume per volume

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10
Q

what is w/w

A

weight by weight
-g per 100g of solution

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11
Q

what is w/v

A

weight by volume -g per 100cm3 of solution

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12
Q

what is v/v

A

volume per volume#
cm3 per 100g of solution

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13
Q

what is ppm and what is it used for

A

parts per million, used for very diluted solutions
1mg / L

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14
Q

what is number of moles of solute for litre of solution

A

number of moles per litre of solution

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15
Q

What is the essential equiptment used for volumetric analysis

A

volumetric flask

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16
Q

why do chemists use standard solutions

A

they often use solutions of known concentration to figure out the concentration of another solution of an unknown conc

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17
Q

what is a standard solution

A

a solution whos conc is accurately known

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18
Q

how is a standard solution prepared

A

its prepared by dissolving a definite, percesily known mass of solute in a suitable solvent to give a definite precisly known volume of solution

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19
Q

primary standard

A

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

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20
Q

samples of primary standard

A

anhydrous sodium carbonate
sodium chloride
potassium dichromate

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21
Q

Describe how you would prepare a standard solution of sodium carbonate

A
  • 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
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22
Q

Why is it possible to make up a standard solution of sodium carbonate directly?

A

Because Na2CO3 is a primary standard, i.e. very pure and stable.

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23
Q

What precaution is taken to ensure that all of the sodium carbonate is transferred from the clock glass to the beaker?

A

the clock glass is rinsed with DI water, these rinslings are transferred to the beaker

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24
Q

why is a stirring rod used

A

speed up the dissolving of sodium carbonate- prevent formation of hard lumps of the sunstance

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25
Q

Why is it necessary to wash the solution off the stirring rod into the beaker?

A

To ensure that none of the sodium carbonate solution is lost

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26
Q

Why are the rinsings from the beaker added to the volumetric flask?

A

To ensure that all of the sodium carbonate solution is transferred to the volumetric flask.

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27
Q

Why is it necessary to be particularly careful when adding the last few drops of water to the volumetric flask?

A

there is danger of overshooting the mark,resulting in a solution of an unknown conc, then you will have to start again

28
Q

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?

A

to ensure a homogenous solution, narrow neck of the slask

29
Q

Why is a beaker, rather than a conical flask, used when the solute is being dissolved?

A

sprout facilitates pouring- stirring is easier because it has a wide neck

30
Q

why is a funnel used

A

minimise the risk of spillage

31
Q

why is Na2CO3 added slowly, with stirring, to the beaker

A

to prevent the formation of hard lumps of sodium carbonate that are hard to dissolve.

32
Q

what is the concentration of a solution dertimined by

A

its dertimined by reacting that solution with another solution of a known concentration ( primary standerd or secondary standard)

33
Q

what is the end point / equivalence point

A

the point at which the two solutions have reacted completely

34
Q

the conc of a solution is recorded by..

A

the volumes of the two solutions at end point

35
Q

Role of a graduated cylinder

A

measured volume, isnt accurate due to wide neck

36
Q

Role of volumetric flask

A

contains a definite amount of a solution.
callibration markto ensure solution is accurate.
mix via inverting (homogenous mixture)
base of meniscus rests on mark

37
Q

Role of pipette

A

designed to draw up a percise amount of solution 25 cm3 usually

38
Q

Role of burette

A

fill above mark and open to ensure bottom is filled w/liquod, no air bubbles.
shows volume decreasing downwards

39
Q

Role of conical flask

A

shape suitable for swirling.
place white tile underneath to see colour change clearly

40
Q

Role of pestle + mortar

A

used to break down any solid into smaller pieces so that it can be easilty dissolved in a solution

41
Q

What is the indicator used?
What are its colour changed

To use the standard solution of sodium carbonate to standardise HCl

A

methyl orange
yellow to pink

42
Q

Describe using the standard solution of sodium carbonate to standardise HCl

A
  • 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
43
Q

describe the apperange of sodium carbonate

A

white solid

44
Q

why must the mass of sodium carbonate dissolved in the water be known accurately

A

so that the conc of the NaCo3 can be calculated accurately

45
Q

why is Na2Co3 a primary standared?

A

it can be obtained in a pure and stable form

46
Q

state two benefits of a volumetric flask for making up the solution

A

the volume of the solutio is accurately known
the design of the solution allows it to be shaken easily to ensure a homogenous solution

47
Q

why is it not recommended to pipette directly from the volumetric flask

A

rick for glass breakage

48
Q

why is it important not to add too much indicator

A

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

49
Q

why do we have to standardise HCl solution

To use the standard solution of sodium carbonate to standardise HCl

A

HCl is not a primary standard

50
Q

why carry the expeirment out more than once

A

more accurate titration figure - average of two readings aggreing withing 0.1 cm3 is used

51
Q

apperance of isolated sodium carbonate

A

white crystalline solid

52
Q

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

A

methly orange
yellow to pink

53
Q

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

A
  • rinse burette,pipette…
  • using pipette,transfer NaOH into conical flask, add indicator.
  • fill burette with HCl
54
Q

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

A

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

55
Q

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

A

methyl red/ phenolphthalein

56
Q

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

A

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

57
Q

what indicator is used and what colour does it change

Dertermination of the concentration of thanoic acid in vinegar

A

phenolphtalein
pink to colourless

58
Q

describe how to dertimine the concentration of thanoic acid in vinegar

A
  • 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
59
Q

Why is the vinegar diluted

Dertermination of the concentration of thanoic acid in vinegar

A

avoid a very small titre,which would reduce the accuracy of the expeirment.
also reduces the amount of vinegar and NaOH needed

60
Q

what is the Indicator used, describe its colour

Dertimination of the amount of water crystallisation in hydrated sodium carbinate

A

methyl orange
yellow to pink

61
Q

Method of dertermining of the amount of water crystallisation in hydrated sodium carbinate

A
  • 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
62
Q

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?

A

It was stoppered, and then inverted several times. To ensure a homogeneous solution.

63
Q

Describe the physical appearance of hydrated sodium carbonate

A

White crystalline solid. However, if larger crystals are purchased, these tend to
have a clear glassy appearance.

64
Q

Explain water of crystallisation.

A

Water chemically bound in the compound, which gives rise to the crystalline form or water
present in definite proportions in crystalline compounds.

65
Q

Name another compound that has water of crystallisation present.

A

Hydrated copper sulfate

Chemistry (21 decks)

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