Chapter 11: Titrations in Analytical Chemistry Flashcards
also called as titrimetric methods
titration methods
involve measuring the volume of a solution of known concentration that is needed to react completely with the analyte
volumetric titration
the mass of the reagent is measured instead of its volume that is needed to react completely with the analyte
gravimetric titrations
the “reagent” is a constant direct electrical current of known magnitude that consumes the analyte.
coulometric titrations
are based on determining the quantity of a reagent of known concentration that is required to react completely with the analyte. The reagent may be a standard solution of a chemical or an electric current of known magnitude.
titration methods
the quantity of charge required to
complete a reaction with the analyte
is the measured quantity
coulometric titrations
is a reagent of known concentration that are used in titrations and in many other chemical analyses or carrying out volumetric titration
standard solution
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. __________ are often required when the rate of reaction between the analyte and reagent is slow or when the standard solution lacks stability.
back-titration
other name for standard solution
standard titrant
TRUE or FALSE
The volume or mass of reagent needed to complete the titration is determined from the difference between the initial and final readings.
TRUE
It is sometimes necessary to add an excess of the standard titrant and then determine the excess amount by ____________ with a second standard titrant
back titration
The ________ in a titration is a theoretical point reached when the amount of added titrant is chemically equivalent to the amount of analyte in the sample
equivalence point
TRUE or FALSE
We cannot determine the equivalence point of a titration experimentally. Instead, we can only estimate its position by observing some physical change associated with the condition of chemical equivalence, which the position of this change is called
TRUE
endpoint
The difference in volume or mass between the equivalence point and the end point is the
titration error
are often added to the analyte solution to produce an observable physical change (signaling the end point) at or near the equivalence point
indicator
is the point in a titration when the amount of
added standard reagent is equivalent
to the amount of analyte
equivalence point
is the point in a titration when a physical change occurs that is associated with the
condition of chemical equivalence
end point
formula of tiration error
titration error= actual volume of reagent required - theoretical volume necessaru to reach the equivalence point
is an ultrapure compound that serves as the
reference material for a titration or for another type of quantitative analysis
primary standard
is a highly purified compound that serves as a reference material in titrations and in other analytical methods
primary standard
important requirements for a primary standard are
high purity
atmospheric stability
absence of hydrate water
modest cost
reasonable solubility in the titration medium
reasonable large molar mass so that relative error is minimized
is a compound whose purity has been
determined by chemical analysis.
The _____________ serves as the working standard material for titrations and for many other analyses
secondary standard
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 exactly known volume of another standard solution.
standardization
carefully determined mass of a primary standard is dissolved in a suitable solvent and diluted to a known volume in a volumetric flask
direct method
the titrant to be standardized is used to titrate (1) a known mass of a primary standard,(2) a known mass of a secondary standard, or (3) a measured volume of another standard solution.
standardization
A standardized titrant is sometimes referred to ______, which its conc is also subjected to a larger uncertainty than is the conc of a primary standard solution
secondary-standard solution
is the number of equivalents of reagent in the same volume.
normal concentration
differ from their volumetric counterparts
in that the mass of titrant is measured rather than the volume
mass (weight) or gravimetric titrations
most common ways for mass titrations is
weight concentration (mole of solute/kg of solvent)
are plots of a concentration-related variable versus titrant volume.
titration curves
is a plot of some function of the analyte or titrant concentration on the y-axis versus titrant volume on the x-axis.
titration curve
the p-function of analyte (or sometimes the titrant) is plotted as a function of titrant volume
sigmoidal curve
measurements are made on both sides of, but well away from, the equivalence point
linear segment curve
TRUE or FALSE
The sigmoidal type offers the advantages of speed and convenience.
TRUE
TRUE or FALSE
The linear segment type is advantageous for reactions that are complete only in the presence of a considerable excess of the reagent or analyte.
TRUE
Advantages of Gravimetric Titrations
- calibration of glassware and tedious cleaning ensuring proper drainage is completely eliminated
- Temperature corrections are unnecessary because the mass (weight) molar concentration does not change with temperature
- Mass measurements can be made with considerably greater precision and accuracy
than can volume measurements. - Gravimetric titrations are more easily automated than are volumetric titrations.
2 most widely used signals to observe endpoint
(1) changes in color due to the reagent (titrant), the analyte, or an indicator and
(2) a change in the potential of an electrode that responds to the titrant concentration or the analyte concentration
a titration error in acid-base titrations that occurs when the pH at which the indicator changes color differs from the pH at the equivalence point
determinate error
This type of error can usually be minimized by choosing the indicator carefully or by making a blank correction.
determinate error
a titration error in acid-base titrations that originates from the limited ability of the human eye to distinguish reproducibly the intermediate color of the indicator
indeterminate error
is performed by slowly adding a 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
TRUE or FALSE
It is sometimes necessary to add an excess of the standard titrant and then determine the excess amount by back-titration with a second standard titrant
TRUE
instruments that can detect end points
calorimeters
turbidimeters
spectrophotometers
temperature monitors
refractometers
voltmeter
current meter
conductivity meter
TRUE or FALSE
purity of such a secondary standard must be established by careful analysis
TRUE
ideal standard solution for a titrimetric method should do the following
be sufficiently stable
react rapidly with the analyte
react more or less completely with the analyte
undergo selective reaction with the analyte
a titrant that is standardized is sometimes referred to as a
secondary-standard solution
TRUE or FALSE
The concentration of a secondary-standard solution is subject to a larger uncertainty than is the concentration of a primary-standard
solution
TRUE
TRUE or FALSE
Many reagents lack the properties required for a primary standard and, therefore, require standardization
TRUE
standard solutions are normally expressed in
molar concentration
normal concentration
refersto a balance and a weighable solution dispenser that are substituted for a buret and its markings
mass titration
formula of molality
mole of solute/ kg of solution
TRUE or FALSE
end point is signaled by an observable physical change near the equivalence point of a titration
TRUE
