Titrations

Question 1

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

Answer 1

titrations

Question 2

substance in the burette in a titration

Answer 2

titrant

Question 3

substance in the flask during titration

Answer 3

titrand

Question 4

types of titration

Answer 4

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

Question 5

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

Answer 5

equivalence point

Question 6

End point is ____ than the equivalence point

Answer 6

larger

titration error

Question 7

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

Answer 7

end point

Question 8

Titration error

Answer 8

V endpoint = V equivalence point

Question 9

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

Answer 9

blank titration

Question 10

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

Answer 10

back titration

Question 11

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

Answer 11

standard solution

Question 12

highly purified comopund that serves as a reference material

Answer 12

primary standard

Question 13

Desired properties of the primary standard include

Answer 13

• 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

Question 14

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

Answer 14

secondary standard

Question 15

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

way of preparing standard solution

Answer 15

direct method

Question 16

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

Answer 16

standardisation

Question 17

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

Answer 17

gravimetric titration

Question 18

Advantages of gravimetric titrations

Answer 18

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

Question 19

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

Answer 19

neutralisation titrations

Question 20

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

Answer 20

strong

Question 21

acid dissociation constant

Answer 21

Ka

Question 22

base dissociation constant

Answer 22

Kb

Question 23

Ka =

Answer 23

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

Question 24

Kb =

Answer 24

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

Question 25

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

Answer 25

polyprotic acids

Question 26

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

Answer 26

weak

Question 27

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

Answer 27

Kjeldahl method

Question 28

Steps of Kjeldahl method

Answer 28

- digestion - neutralisation and distillation of NH3 - Collection og NH3 in excess HCl - Titation of unreacted HCl with NaOH

Question 29

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

Answer 29

Ammonium salts

Question 30

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

Answer 30

nitrates and nitrites

Question 31

volumetric method involves reaction of metal with ligand to form complex

Answer 31

complexation titrations

Question 32

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

Answer 32

complex formation

Question 33

Advantages of EDTA

Answer 33

- cheap, commercially available - versatile, reacts with most metals - forms stable complexes with most metals - reacts in 1:1 ration with metals

Question 34

Disadvantage of EDTA

Answer 34

- its reaction is reversible, requires alkaline buffer - it's non-selective reagent

Question 35

form coloured complex with metals

Answer 35

metallochromic indicators ## Footnote Examples include EBT, Murexide, xylenol orange

Question 36

Requirements for sucessful use of metal indicators

Answer 36

- 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

Question 37

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

Answer 37

Buffer solution

Question 38

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

Answer 38

Buffer solution

Question 39

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

Answer 39

Buffer solution

Question 40

An ________ buffer is used in complexometric titrations

Answer 40

alkaline