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Analytical Chemistry > Titrimetric methods of analysis ✅ > Flashcards

Titrimetric methods of analysis ✅ Flashcards

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1
Q

What is titrimetric (volumetric) analysis?

A

The quantity of material is estimated by visual volumetric analysis method, measuring the volume of known concentration agent solution, which has reacted with this material.

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2
Q

What is a titration?

A

Titration is a common method of determining the amount or concentration of an unknown substance.

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3
Q

When is a titration easy to use?

A

When the quantitative relationship between two reacting solutions is known.

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4
Q

What type of data do titrations give?

A

quantitative data

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5
Q

What are the two types of titrimetric methods?

A

1) visual
2) instrumental

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6
Q

What is a titrant ?

A

known concentration (in burrette)

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7
Q

What is a titrand?

A

Solution with unknown concentration, located in the volumetric flask.
Also known as the analyte.

“and”? what is the final concentration?

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8
Q

What are the 4 classifications of volumetric method?

A
  • neutralization
  • precipitation
  • complexometry
  • redoxometry
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9
Q

What type of reaction occurs when there is an acid and base titration? What does it produce?
How can the endpoints be measured?

A

neutralization reaction occurs
- products: salt and water (combination of hydrogen and hydroxide ions)
- endpoints measured by indicator or pH meter

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10
Q

What indicators do precipitation reactions use?

A

chromates eg. potassium dichromate (K2Cr2O7)

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11
Q

What reacts with chromate? What colour precipitate does it form?

A

Ag+ forms a reddish precipitate with chromate

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12
Q

What is the basis between the precipitation titration reaction?

A

The titrant
forms an insoluble
product with the analyte.

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13
Q

What is an example of a precipitation reaction?

A

NaCl + AgNO3 → AgCl +
NaNO3

(chloride ion with silver nitrate solution)

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14
Q

What is complexometry?

A

The titrant (complexing agent) forms a water-soluble complex with the analyte, a metal ion.

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15
Q

What is redoxometry?

A
  • redox titration
  • reduction and oxidation occurs
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16
Q

What is reduction? What is oxidation?

A

Reduction:
electron gain
H+ gain
oxygen loss

Oxidation:
electron loss
H+ loss
oxygen gain

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17
Q

State an equation for oxidation and reduction.

A

Oxidation:
Na–> Na+1 + e-

Reduction:
Cl + e- –> Cl-1

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18
Q

What is a titration?

A

analysis process, when a solution is dropped into another known solution’s volume till the equivalence point is reached.

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19
Q

What is an equivalence point?

A
  • practical and experimentally determinable point
  • the moment when the reactants have reacted completely, with no excess or deficit if either the analyte of titrant,
  • the center of the vertical line
  • moles of base = moles of acid
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20
Q

What is the endpoint? How is it known?

A
  • when the two chemicals (acid and base) neutralize each other
  • seen by a change in colour
  • the point at which physical change associated with the condition of equivalence.
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21
Q

What is an endpoint in the ideal world?

A
  • the color change would happen when you mix the two solutions
    together in exactly equation proportions.
  • endpoint=equivalence point
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22
Q

What is the titration error?

A

the difference in volume between the equivalence point and the end point.

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23
Q

What are indicators?

A

reagents often added to the analyte
solution in order to give an observable physical change at the end point or near the equivalence point.

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24
Q

What is concentration?

A

A property of a mixture
calculated by dividing one amount by another.

25
Q

What is molarity?

A

Molarity (M)
- the number of gram moles of reagent that is contained in one liter solution.

Cm=nA/V

M= number of moles/volume of solution

MOLARITY = MOLES / VOLUME (ITY)

26
Q

What is normality?

A

The number of gram equivalents contained in one liter of solution.

Cn= number of equivalent / volume (L)

Cn= m/(E * V)
m- solute’s mass, g;
E- solute’s equivalent;
V- solution’s volume, L.

NORMALITY: equivalent/volume

27
Q

What is percent concentration?

A

Describes how much grams of material is dissolved in 100 grams of solution.

C%= m(substance)/m(solution) * 100%

28
Q

What is weight by weight concentration?

A

if mass is used

29
Q

What is weight by volume concentration?

A

If volume is used for the solvent.

30
Q

What is the titer? How can one calculate it?

A

number of solute’s grams in 1cm3 (ml) of the solution (g/cm3).

T= Cn * E /1000 (g/ml)(g/cm^3)

31
Q

What is the law of equivalent proportions?

A

Titrant vs Analyte
Cn1 * V1 = Cn2 * V2

V1, V2 – titrant and analytes
volumes, cm^3 (ml);
Cn1, Cn2 – titrant and analytes
concentrations of equivalent
(normality; eqv/l).

32
Q

Where is the titrant? Where is the analyte?

A

titrant- in burette
analyte- in volumetric flask

33
Q

What is the mathematical expression of equivalence point?

A

Cn1 * V1 = Cn2 * V2

V1, V2 – titrant and analytes
volumes, cm^3 (ml);
Cn1, Cn2 – titrant and analytes
concentrations of equivalent
(normality; eqv/l).

34
Q

What is the difference between accuracy and precision?

A

accuracy: wether the answer is correct.
- the agreement bewteen a measured and accepted value)

precision: wether all trial answers align.
- the reproducibility of multiple measurements
- the degree of agreement between replicate measurements of the same quantity

35
Q

How is accuracy determined?

A
  • requires calibration of the analytical method with a known standard
36
Q

What does the accuracy and reliabiliy of titrations depend on?

A
  • precision of measuring instruments;
  • purity of reagent;
  • analysts clasification;
  • characteristics of analysis method.
37
Q

What is a pipette?

A

vessel, used to suck, to drop and to measure liquid.

38
Q

What is a Mohr pipette?

A

A pipette which measures only one, definite
and marked on it volume.

39
Q

What is a graduated pipette?

A

A pipette which allows measurement of any volume that would not exceed the volume of pipette’s graduated section.

40
Q

If a graduated pipette has a 0.1 ml scale, when what is its precision?

A

0.005ml

41
Q

What is an automatic micro pipette?

A

An instrument, used to suck, to drop and to measure liquid.

42
Q

What is a burette?

A

Glass tube (generally with
0.1 ml scale), used to drop and to
measure liquid volume

43
Q

What is a volumetric flask used for?

A

Flask used to make up a solution of fixed volume very accurately.

44
Q

What is a standard solution (titrants)? How is it prepared?

A

It is a reagent of known concentration
that is used to carry out a titrimetric
analysis.

The standard solution is prepared by
dissolving an accurate weight of pure
reagent in water this is then diluted to
an exactly known volume.

45
Q

What is an ideal standard solution?

A
  • Be sufficiently stable
  • React rapidly with the analyte
  • React more or less completely with the analyte
46
Q

What is a primary standard substance?

A

a highly purified compound that serves as a reference material in all volumetric titrimetric methods.

47
Q

What are the requirements of primary standard substances?

A
  • It should be 100% pure.
  • It should be stable to drying temperatures.
  • It should be readily available.
  • It should have a high formula weight (to minimize weighing error).
  • It should posses the properties required for a titration (soluble and react rapidly).
48
Q

How are titration solutions prepared?

A

Prepared from materials, which composition changes depending on instability, volatility, hygroscopicity, ability to react with surrounding CO2, O2 or other causes.

49
Q

How is the concentration of the titrated solution determined?

A

Estimated by titrating with
standard solution.

50
Q

What is a neutralization reaction?

A

Reaction between an acid and a base which produces a neutral solution (pH = 7).

acid^+ + base^− → salt + water

51
Q

What changes occur in the process of a titration?

A

the concentration of H+ ions and pH values changes.

52
Q

What are the different types of neutralization. reactions? What are their products and reactants?

A

1) strong base + strong acid —> salt + water
2) weak base + strong acid —> salt + water
3) strong base + weak acid —> salt + water
4) weak base + weak acid —> salt + water

53
Q

What is another substance which should be used in neutralization titrations (colour)?

A

Substances, which react in neutralization reaction, are mostly colorless, so indicators which color depends on medium pH are used.

54
Q

What are indicators?

A

weak organic acids or alkali, which
dissociated and not dissociated forms differ in color.

55
Q

What are the different types of indicators? What are their original colours?

A

Methyl Yellow Red 2.4-4.0 yellow
Methyl Orange Red 3.2-4.4 yellow
Methyl Red Red 4.2-6.2 yellow
Lacmus Red 5.0-8.0 blue
Phenolphthalein Colorless 8.0-9.8 mauve
Alizarin Yellow yellow 10.1-12.0 violet

56
Q

What indicator should one use for the titration of a strong acid with a strong base? What is the colour change?

A

methyl orange
red —> orange–> yellow

hard rock meth

57
Q

What forms when reacting a strong acid with a stronhg alkali?

A

hydrolysis of salt does not occur.

no salt, all inhaled

58
Q

What is the difference between acid strength and concentration?

A
  • The strength of an acid is related to the proportion of it which has reacted with water to produce ions.
  • The concentration tells you about how much of the original acid is dissolved in the solution.
59
Q

What indicator is used for testing a weak acid with a strong alkaline? What is the colour change?

A

phenolophtalein

clear in acid
colourless –> light pink in neutral –> dark pink in base

titrate until mauve

Analytical Chemistry (12 decks)

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