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Instrumental and Analytical Chemistry > Titrations > Flashcards

Titrations Flashcards

1
Q

based on determining the quantity of a reagent of known concentration that is required to react completely with the analyte

A

titrations

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2
Q

substance in the burette in a titration

A

titrant

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3
Q

substance in the flask during titration

A

titrand

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4
Q

types of titration

A
  • acid-base
  • gravimetric
  • complexometric titrations: metal-ligand complexation
  • redox titration
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5
Q

occurs when the quantity of added titrant is the EXACT amount necessary for stoichiometric reaction with the analyte

A

equivalence point

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6
Q

End point is ____ than the equivalence point

A

larger

titration error

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7
Q

what we actually measure in a titration which is marked by a sudden physical change, such as the indicator colour or an electrode potential

A

end point

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8
Q

Titration error

A

V endpoint = V equivalence point

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9
Q

carried out by titrating a fixed and known concentration of titrant into a solvent with zero analyte.

A

blank titration

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10
Q

process in which the excess of a standard solution used to consume an analyte is determined by titration with a second standard solution

A

back titration

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11
Q

reagent of known concentration that is used to carry out a volumetric titration

A

standard solution

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12
Q

highly purified comopund that serves as a reference material

A

primary standard

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13
Q

Desired properties of the primary standard include

A
  • high purity
  • stability in air
  • absence of hydrated water molecules
  • moderate cost and easy availability
  • solubility in the titration solutions
  • large formula weight (molecular weight) since this minimises weighing errors
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14
Q

compound which does not meet all the requirements of a primary standard

A

secondary standard

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15
Q

a primary standard compound is carefully weighed and dissolved in an exactly known volume of solution

way of preparing standard solution

A

direct method

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16
Q

the prepared standard solution is standardised by using it to titrate
- a carefully weighed primary standard compound
- a carefully weighed secondary standard compound
- a carefully weighed volume of another standard solution

way of preparing standard solution

A

standardisation

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17
Q

titation where the mass of titrant is measured rather than the volume

A

gravimetric titration

18
Q

Advantages of gravimetric titrations

A
  1. Calibration of glassware and tedious cleaning to ensure propert drainage are completely eliminated
  2. temperature corrections are unnecessary because the mass (weight) molar concentration does not change with temperature,
  3. mass measurements can be made with considerably higher precision and accuracy than volume measurements can
  4. Gravimetric titrations are more easily automated than volumetric titrations
19
Q

used to determine the amounts of acids and bases and to monitor the progress of reactions that produce or consume hydrogen atoms

A

neutralisation titrations

20
Q

standard reagents used in acid/base reactions are always ________ acids/bases

A

strong

21
Q

acid dissociation constant

A

Ka

22
Q

base dissociation constant

A

Kb

23
Q

Ka =

A

[H+][A-]/[HA]

24
Q

Kb =

A

[HB+][OH-]/[B]

25
Q

Capable of losing more than a single proton per molecule in acid-base reactions. In other words, acids that have more than one ionisable H+ atomm per molecule. Protons are lost through several stages

A

polyprotic acids

26
Q

acid/base indicator is a ____ organic acid or organic base

A

weak

27
Q

widely used for estimating the nitrogen content of foodstuffs, fertilizers, and other substances. It can be used to measure the protein content of foods too.

https://www.britannica.com/science/Kjeldahl-method

A

Kjeldahl method

28
Q

Steps of Kjeldahl method

A
  • digestion
  • neutralisation and distillation of NH3
  • Collection og NH3 in excess HCl
  • Titation of unreacted HCl with NaOH
29
Q

determined by conversion to ammonia with strong base followed by distillation. Ammonia is collected and titated as in the Kjeldahl method

A

Ammonium salts

30
Q

to determine these ions they are first reduced to ammonium ion by Devarda’s alloy or Arnd’s alloy. Granules of the alloy are introduced into a strongly alkaline solution of the sample in Kjedahl’s flask. The ammonia is distilled after reaction is complete

A

nitrates and nitrites

31
Q

volumetric method involves reaction of metal with ligand to form complex

A

complexation titrations

32
Q

a type of acid-base reaction according to lewis concept where metal ion is lewis acid and ligand is lewis electron donor

A

complex formation

33
Q

Advantages of EDTA

A
  • cheap, commercially available
  • versatile, reacts with most metals
  • forms stable complexes with most metals
  • reacts in 1:1 ration with metals
34
Q

Disadvantage of EDTA

A
  • its reaction is reversible, requires alkaline buffer
  • it’s non-selective reagent
35
Q

form coloured complex with metals

A

metallochromic indicators

Examples include
EBT, Murexide, xylenol orange

36
Q

Requirements for sucessful use of metal indicators

A
  • M/EDTA complex is more stable than M/Ind complex
  • Indicator Free colour should be distinguished from M/Ind colour
  • Most metal indicators are acid-base indicators so their solour changes due to pH
  • Indicator is not necessary to be specific but at least selective
37
Q

used to resist the change in pH. All reactions between metal ions and EDTA are pH dependent and therefore a change in pH could lead to a non-quantitative improper reaction between metal ion and EDTA

A

Buffer solution

38
Q

its role is to shift the reaction between EDTA and metal forward to prevent the reversibility of the reaction

A

Buffer solution

39
Q

make colour change at end point due to change in metal concentration not due to pH as most metal indicators are also acid base indicators

A

Buffer solution

40
Q

An ________ buffer is used in complexometric titrations

A

alkaline

Instrumental and Analytical Chemistry (5 decks)

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