Titrimetric methods of analysis ✅ Flashcards
What is titrimetric (volumetric) analysis?
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.
What is a titration?
Titration is a common method of determining the amount or concentration of an unknown substance.
When is a titration easy to use?
When the quantitative relationship between two reacting solutions is known.
What type of data do titrations give?
quantitative data
What are the two types of titrimetric methods?
1) visual
2) instrumental
What is a titrant ?
known concentration (in burrette)
What is a titrand?
Solution with unknown concentration, located in the volumetric flask.
Also known as the analyte.
“and”? what is the final concentration?
What are the 4 classifications of volumetric method?
- neutralization
- precipitation
- complexometry
- redoxometry
What type of reaction occurs when there is an acid and base titration? What does it produce?
How can the endpoints be measured?
neutralization reaction occurs
- products: salt and water (combination of hydrogen and hydroxide ions)
- endpoints measured by indicator or pH meter
What indicators do precipitation reactions use?
chromates eg. potassium dichromate (K2Cr2O7)
What reacts with chromate? What colour precipitate does it form?
Ag+ forms a reddish precipitate with chromate
What is the basis between the precipitation titration reaction?
The titrant
forms an insoluble
product with the analyte.
What is an example of a precipitation reaction?
NaCl + AgNO3 → AgCl +
NaNO3
(chloride ion with silver nitrate solution)
What is complexometry?
The titrant (complexing agent) forms a water-soluble complex with the analyte, a metal ion.
What is redoxometry?
- redox titration
- reduction and oxidation occurs
What is reduction? What is oxidation?
Reduction:
electron gain
H+ gain
oxygen loss
Oxidation:
electron loss
H+ loss
oxygen gain
State an equation for oxidation and reduction.
Oxidation:
Na–> Na+1 + e-
Reduction:
Cl + e- –> Cl-1
What is a titration?
analysis process, when a solution is dropped into another known solution’s volume till the equivalence point is reached.
What is an equivalence point?
- 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
What is the endpoint? How is it known?
- 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.
What is an endpoint in the ideal world?
- the color change would happen when you mix the two solutions
together in exactly equation proportions. - endpoint=equivalence point
What is the titration error?
the difference in volume between the equivalence point and the end point.
What are indicators?
reagents often added to the analyte
solution in order to give an observable physical change at the end point or near the equivalence point.
What is concentration?
A property of a mixture
calculated by dividing one amount by another.
What is molarity?
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)
What is normality?
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
What is percent concentration?
Describes how much grams of material is dissolved in 100 grams of solution.
C%= m(substance)/m(solution) * 100%
What is weight by weight concentration?
if mass is used
What is weight by volume concentration?
If volume is used for the solvent.
What is the titer? How can one calculate it?
number of solute’s grams in 1cm3 (ml) of the solution (g/cm3).
T= Cn * E /1000 (g/ml)(g/cm^3)
What is the law of equivalent proportions?
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).
Where is the titrant? Where is the analyte?
titrant- in burette
analyte- in volumetric flask
What is the mathematical expression of equivalence point?
Cn1 * V1 = Cn2 * V2
V1, V2 – titrant and analytes
volumes, cm^3 (ml);
Cn1, Cn2 – titrant and analytes
concentrations of equivalent
(normality; eqv/l).
What is the difference between accuracy and precision?
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
How is accuracy determined?
- requires calibration of the analytical method with a known standard
What does the accuracy and reliabiliy of titrations depend on?
- precision of measuring instruments;
- purity of reagent;
- analysts clasification;
- characteristics of analysis method.
What is a pipette?
vessel, used to suck, to drop and to measure liquid.
What is a Mohr pipette?
A pipette which measures only one, definite
and marked on it volume.
What is a graduated pipette?
A pipette which allows measurement of any volume that would not exceed the volume of pipette’s graduated section.
If a graduated pipette has a 0.1 ml scale, when what is its precision?
0.005ml
What is an automatic micro pipette?
An instrument, used to suck, to drop and to measure liquid.
What is a burette?
Glass tube (generally with
0.1 ml scale), used to drop and to
measure liquid volume
What is a volumetric flask used for?
Flask used to make up a solution of fixed volume very accurately.
What is a standard solution (titrants)? How is it prepared?
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.
What is an ideal standard solution?
- Be sufficiently stable
- React rapidly with the analyte
- React more or less completely with the analyte
What is a primary standard substance?
a highly purified compound that serves as a reference material in all volumetric titrimetric methods.
What are the requirements of primary standard substances?
- 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).
How are titration solutions prepared?
Prepared from materials, which composition changes depending on instability, volatility, hygroscopicity, ability to react with surrounding CO2, O2 or other causes.
How is the concentration of the titrated solution determined?
Estimated by titrating with
standard solution.
What is a neutralization reaction?
Reaction between an acid and a base which produces a neutral solution (pH = 7).
acid^+ + base^− → salt + water
What changes occur in the process of a titration?
the concentration of H+ ions and pH values changes.
What are the different types of neutralization. reactions? What are their products and reactants?
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
What is another substance which should be used in neutralization titrations (colour)?
Substances, which react in neutralization reaction, are mostly colorless, so indicators which color depends on medium pH are used.
What are indicators?
weak organic acids or alkali, which
dissociated and not dissociated forms differ in color.
What are the different types of indicators? What are their original colours?
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
What indicator should one use for the titration of a strong acid with a strong base? What is the colour change?
methyl orange
red —> orange–> yellow
hard rock meth
What forms when reacting a strong acid with a stronhg alkali?
hydrolysis of salt does not occur.
no salt, all inhaled
What is the difference between acid strength and concentration?
- 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.
What indicator is used for testing a weak acid with a strong alkaline? What is the colour change?
phenolophtalein
clear in acid
colourless –> light pink in neutral –> dark pink in base
titrate until mauve
