Analytical Chemistry Chapter 6 Flashcards
Include a large and powerful group of quantitative procedures based on measuring the amount of a reagent of known concentration (standard solution titrant) that is consumed by an analyte.
Is a term that includes a group of analytical methods based on determining the quantity of a reagent of known concentration that is required to react completely with the analyte.
Titrimetric methods
Titrimetry
Involves measuring the volume of a solution of known concentration that is needed to react essentially completely with the analyte.
Volumetric Titrimetry
It differs only because the mass of the reagent is measured instead of its volume.
Gravimetric Titrimetry
The “reagent” is a constant direct electrical current of known magnitude that consumes the analyte; here, the time required to complete the electrochemical reaction is measured.
Coulometric Titrimetry
Titrimetric methods are widely used for routine determinations. Why?
🍄Rapid
🍄Convenient
🍄Accurate
🍄Readily automated
Used for the determination of naturally occurring and synthetic acids and bases and, in addition, molecular species that can be converted to acids or bases by chemical reaction.
Neutralization titrations
Includes a group of analytical methods bașed on determining the quantity of a reagent of known concentration that is required to react completely with the analyte.
The reagent may be a:
Titrimetry
🍒standard solution of a chemical
🍒electric current of known magnitude
Is a type of titimetry in which the standard reagent is measured volumetrically.
Volumetric Titrimetry
Is a type of titrimetry in which the quantity of charge in coulombs required to complete a reaction with the analyte is measured.
Coulometric Titrimetry
Is a reagent of-known concentration: that is used to carry out a titrimetric analysis.
standard solution (or a standard titrant)
A _______ is performed by adding standard-solution from a buret or other liquid-dispensing device to a solution of the analyte until the reaction between the two is judged complete.
titration
The volume of a reagent needed to complete the titration is determined from the _______.
Difference between the initial and final volume readings.
The ______ in a titration is reached when the amount of added titrant is chemically equivalent to the amount of analyte. in the sample.
equivalence point
What is the equivalence point of:
🍦titration of NaCl with AgNO3
🍦titration of H2SO4 with NaOH
🍦1 mol of Ag ion has been added for each mole of chloride ion in the sample.
🍦 2 mol of base for each mole of acid.
A _____ is a reagent of known concentration that is used in a titrimetric analysis.
standard solution
Is a process in which a standard reagent is added to a solution of an analyte until the reaction between the analyte and reagent is judged to be complete.
Titration
Is a process in which the excess of a standard solution used to consume an analyte is determined by titration with a second standard solution.
Often required when the rate of reaction between the analyte and reagent is slow or when the standard solution lacks stability.
Back-titration
The equivalence point of a titration cannot be determined experimentally. What to do instead?
This change is called:
we can only estimate its position by:
observing physical change associated with the condition of equivalence.
♡end point for the titration
The difference in volume or mass between the equivalence point and the end point
titration error
Are often added to the analyte solution to give an observable physical change (the end point) at or near the equivalence point. We shall see that large changes in the relative concentration of analyte or titrant occur in the equivalence point region. These concentration changes cause the ____ to change the appearance.
Typical indicator changes include the:
Indicators
appearance or disappearance of a color
a change in color
or the appearance or disappearance of turbidity
We often use _____ to detect end points. These instruments respond to certain properties of the solution that change in a characteristic way during the titration.
Instruments for detecting end points include:
instruments
colorimeters
turbidimeters
temperature
monitors
voltmeters
current meters
conductivity meters
The ____ is the point in a titration when the amount of added standard reagent is equivalent to the amount of analyte.
Related to the amounts of reactants consumed
equivalence point
The _____ is the point in a titration when a physical change occurs that is associated with the condition of chemical equivalence.
end point
In volumetric methods; the titration error Et is given by:
Et
Veq
Vep
Et = Vep - Veq
Where Veq is the theoretical volume of reagent required to reach the equivalence point
and Vep is the actual volume used to arrive at the end point
In volumetric methods; the titration error Et is given by:
where Veq is the theoretical volume of reagent required to reach the equivalence point, and Vep.is the actual volume-used to arrive at the end. point.
A ________ is a highly purified compound that serves as a reference material in all volumetric and mass titrimetric methods.
The accuracy of a method is critically dependent on the properties of this compound. Important requirements for a primary standard are:
primary standard
High purity
Atmospheric stability
Absence of hydrate water (so that the composition of the solid does not change with variations in relative humidity)
Ready availability at modest cost
Reasonable solubility in the titration medium
Reasonably large molar mass so that the relative error associated with weighing the standard is minimized.
A _______ is an ultapure compound that serves as the reference material for the titrimetric method of analysis.
A _____ is a compound whose purity has been established by chemical analysis and that serves as the reference material for a titrimetric method of analysis.
primary standard
secondary standard
The ideal standard solution for a titrimetric method will:
- Be sufficiently stable so that it is only necessary to determine its concentration once
- React rapidly with the analyte so that the time required between additions of reagent ıs minimized
- React completely with the analyte so that satisfactory end points are realized
- Undergo a selective reaction with the analyte that can be described by a balanced equation.
The accuracy of a titrimetric method can be no better than the accuracy of the concentration of the standard solution used in the titration.
Two basic methods are used to establish the concentration of such solutions:
Direct method
Standardization
a carefully weighed quantity of a primary standard is dissolved in a suitable solvent and diluted to a known volume in a volumetric fiask.
The titrant to be, standardized is used to titrate:
Direct method
Standardization
(1) a weighed quantity of a primary standard
(2) a weighed quantity of a secondary standard, or
(3) a measured volume of another standard solution
A titrant that is standardized against a secondary standard or against another standard solution is sometimes referred to as a ________.
secondary standard solution
In a ______, the concentration of a volumetric solution is determined by titrating it against a carefully measured quantity of a primary or secondary standard or an accurately known volume of another standard solution.
standardization
The concentrations of standard solutions are generally expressed in units of either.
The first gives the _____ contained in one liter of solution (no. mol analyte present mol standard reagent added),
and the second gives the _____ in the same volume. (no. eq analyte- present: = no.eq standard reagent added).
molarity c or normality cN.
number of moles of reagent
number of equivalents of reagen
Is the normality of a solution can never be specified without knowledge about how the solution will be used?
One equivalent weight of a substance paricipating in a neutralization reaction is that amount of substance (molecule, ion, or paired ion such as NaOH) that either reacts with or supplies 1 mol of hydrogen ions in that reaction.
Yes
Most _____ are based on two pairs of fundamental equations that are derived from definitions of millimole, mole, and molar concentration.
volumetric calculations
The law of conservation of mass states that _____.
Equation 6-2 is simplified as:
C1V1= C2V2
Where C1’s and V1’s are concentrations and volumes before and after change.
Other forms of expression,
M1V1 = M2V2=
N1V1=N2V2
C1V1 = C2V2
mass remains constant in chemical change
🍭mass (in mols or no. meq) remains constant before and after change.
🍭amount (in mols) = mass/molar mass or mass/MW
🍭amount (in no. eq) = mass/eqw for normality calculation
🍭for percentage calculation.
Two types of volumetric calculations
The first involves computing the___
The second involves _____.
Both types are based on three algebraic relationships:
1️⃣molarity of solutions that have been standardized against either a primary standard or another standard solution.
2️⃣calculating the amount of analyte in a sample from titration data.
⚪️⚪️⚪️
Two of these are Equations 6-2 and 6-4, which are based on millimoles and milliliters.
The third relationship is the stoichiometric ratio of the
number of millimoles of the analyte-to the number of millimoles of titrant.
Basic principle
aA +bB -> Products
A:
B:
a and b are the:
Titrant (standard solution)
Analyte (unknown )
number of moles of each
Requirments inTitration
1-stoichiometric reaction
2- rapid rate reaction 3- quantitative reaction (99.9%complete at stoichiometry) 4-have a defined end or equivalence point
Related to the amounts of reactants consumed.
Related to the physical sign that is associated with the condition of chemical equivalence.
Ideally, the _____ one coincide. (variation may be to _____)
Equivalence point
End point
end point and equivalent point
color change of indicator
Standard Solution
A process in which concentration of a volumetric solution is determined by titrating it with a known mass of a primary standard.
A primary standard
A secondary standard
Standardization
This is performed by adding a standard solution from a buret or other liquid- dispensing device to a solution of the analyte until the point at which the reaction is believed to be complete.
Titration
PRIMARY STANDARD
• HIGH PURITY
• ATMOSPHERIC STABILITY
• INDEPENDENT OF HUMIDITY
• MODEST COST
• LARGE MOLAR MASS
• NON HGYROSCOPIC
Types of titrimetry
1- Precipitation:
2- Acid Base titration:
3- Complex formation
4- Oxidation Reduction
- (Ag+) + (CI-) -> AgCI (s)
- (OH-) + (HA) -> (A-) +H2O
- (EDTA2-) + (Ca2+) -> EDTA Ca.xH20
- (MnO4-) + (5Fe2+) + (8H+) -> (5Fe3+) + (Mn2+) + (4H20)
Calculations with Molarity
Is the formula weight of a substance expressed in grams
Number of moles =
Number of m.moles =
Molarity=
The mole
weight in grams/formula weight
weight in milligrams/formula weight
Moles/Liter or mmoles/ml
Moles=
Weight (g) =
m.Moles=
Weight (mg) =
Volume (L). (M)
Volume (L). (M). form weight (g)
Volume (ml). (M)
Volume (ml). (M) . form weight (g)
