Analytical Chemistry Chapter 5 Flashcards
The position of most solution equilibria depends on the ______ of the medium, even when the added electrolyte contains no ion in common with those involved in the equilibrium.
electrolyte concentration
If an electrolyte, such as ______ is added to this solution, the color of the triiodide ion becomes less intense. This decrease in color intensity indicates that the concentration of I3 has decreased and that the equilibrium has been shifted to the left by the added electrolyte.
🍉barium nitrate
🍉potassium sulfate
🍉sodium perchlorate
_____ is a plot of the product of the molar hydronium and hydroxide ion concentration (X 10^4) as a function of the concentration of sodium chloride.
This concentration-based ion product is designated ___.
At low sodium chloride concentrations, K becomes independent of the electrolyte concentration and is equal to ______, which is the _______ constant for water, Kw.
A relationship that approaches a constant value as some variable (here, the electrolyte concentration) approaches zero is called a ______; the constant numerical value observed at this limit is referred to as a _______.
Curve A
Kw
1.00 X 10^14
thermodynamic ion-product
limiting law
limiting value
The vertical axis for ____ in Figure 5-1 is the product of the molar concentrations of barium and sulfate ions (X 10^10) in saturated solutions of barium sulfate. This concentration-based solubility product is designated as ____.
At low electrolyte concentrations, K’sp has a limiting value of _______, which is the accepted thermodynamic value of Ksp for barium sulfate.
curve B
Ksp
1.1x10^10
_____ is a plot of _____ the concentration quotient for the equilibrium involving the dissociation of acetic acid as a function of electrolyte concentra- tion.
Here again, the ordinate function approaches a limiting value _____, which is the thermodynamic acid dissociation constant for acetic acid.
Curve C
K’a (x10^5)
Ka
_____ is a plot of _____ the concentration quotient for the equilibrium involving the dissociation of acetic acid as a function of electrolyte concentra- tion.
Here again, the ordinate function approaches a limiting value _____, which is the thermodynamic acid dissociation constant for acetic acid.
Curve C
K’a (x10^5)
Ka
The _______ in Figure 5-1 represent the ideal behavior of the solutes.
dashed lines
______ are often indicated by adding a prime mark.
Examples are:
As the electrolyte concentration becomes very small, concentration-based equilibrium tion constants approach their thermodynamic values: Kw, Ksp, Ka.
Concentration-based equilibrium constants
🍇K’w
🍈K’sp
🍊K’a
The magnitude of the electrolyte effect is highly dependent on the ____ of the participants in an equilibrium.
When only neutral species are involved, the position of equilibrium is essentially independent of ______.
With _____, the magnitude of the electrolyte effect increases with charge.
charge
Electrolyte concentration
Ionic participants
Systematic studies have shown that the effect of added electrolyte on equilibria is ______ of the chemical nature of the electrolyte but depends on a property of the solution called the _______.
independent
ionic strength
Results from the electrostatic attractive repulsive forces that exist ‘between the ions of an electrolyte and the ions involved in an equilibrium. These forces cause. each ion from the dissociated reactant to be surrounded by a sheath of solution that contains a slight excess of electrolyte ions of opposite charge.
electrolyte effect
Chemists use the term ___, to account for the effects of electrolytes on chemical equilibria.
The activity, or effective concentration, of species X depends on the ionic strength of the medium and is defined as:
ax - Yx[X’]
where ____ is the activity of X,
[X] is its _______, and
yx is a dimensionless quantity called the ________.
activity (a)
ax
molar concentration
activity coefficient
The _____ is more useful than concentration in medical diagnosis since it reflects the body’s conditious.
It’s also the measuring unit by potentiometry but none other instrumental methods.
value of activity
The _______ is a measure of the effectiveness with which that species influences an equilibrium in which it is a participant.
In very dilute solutions, where the ionic strength is minimal, this effectiveness becomes constant, and the activity coefficient becomes unity.
Under such circumstances, the activity and the molar concentration are identical (as are therodynamic and concentra- tion equilibrium constants).
T OR F。As the ionic strength “decreases”, however, an ion loses some of its effectiveness, and its activity coefficient decreases.
activity coefficient of a species
Increases
In solutions that are not too concentrated, the activity coefficient for a given species is independent of the nature of the ______ and dependent only on the ________.
- For a given ionic strength, the activity coefficient of an ion _______ from unity as the charge carried by the species increases. This effect is shown in Figure 5-2. The activity coefficient of an uncharged molecule is approximately unity, regardless of ionic strength.
At any given ionic strength, the activity coefficients of ions of the same charge are approximately _______. The small variations that do exist can be correlated with the effective diameter of the hydrated ions.
The ______ of a given ion describes its effective behavior in all equilibria in which it participates.
electrolyte
ionic strength
departs farther
equal
activity coefficient
The _______ is a measure of its effective concentration as determined by the lowering of the freezing point of water, by electrical conductivity, and by the mass- action effect.
activity of a species
In 1923, _________ used the ionic atmosphere model to derive a: theoretical expression that permits the calculation of activity coefficients of ions from their charge and their average size.
This equation, which has become known as the ______
where:
Yx= activity coefficient of the species X
Zx= charge on the species X
u= ionic strength of the solution
ax = effective diameter of the hydrated ion X in nanometers (10-^9 m)
The constants _______ are applicable to aqueous solutions at 25°C; other values must be used at other temperatures.
P. Debye and E. Hückel
Debye-Hückel equation
Where:
🪶activity coefficient of the species X
🐚charge on the species X
🕸ionic strength of the solution
🍁effective diameter of the hydrated ion X in nanometers (10-^9 m)
0.51 and 3.3
He was born and educated in Europe but became Professor of Chemistry at Cornell University in 1940.
He was moted for his work in several different arcas of chemistry, including electrolyte solutions, X-ray diffraction, and the propertics of polar molccules.
He received the 1936 Nobel Prize in Chemistry.
Peter Debye
Thus, in solutions of very low ionic strength, the _____ can be used to calcalate approximate activity coefficients.
Debye-Hückel Limiting Law (DHLL)
______ has calculated values of ax for numerous ions from a variety of experimental data.
J. Kielland
Cell B5, refers to cell B5
Circular Reference
Effect causes both this equilibrium and the solubility equilibrium to shift to the right; an increase in solubility results.
an effect that suppresses the ionization of an electrolyte when another electrolyte (which contains an ion which is also present in the first electrolyte, i.e. a common ion) is added
Common-ion effect
Three types of algebraic equations are used in solving multiple-equilibrium problems:
🌨equilibrium-constant expressions
🌧mass-balance equations
🌧single charge-balance equation
Relate the equilibrium concentrations of various species in a solution to one another and to the analytical concentrations of the various solutes.
They are derived from information about how the solution was prepared and from a knowledge of the kinds of equilibria established in the solution.
Mass-balance or material-balance equations
The term _______, although widely used, is somewhat misleading because such equations are really based on balancing _____ rather than _____. On the other hand, since all species are in the same volume of solvent, equating masses to concentations does not create a problem.
mass-balance equation
concentrations
masses
For a slightly soluble salt with a 1:1 stoichiometry, the equiļibrium concentration of the cation is equal to equilibrium concentration of the anion, This equality is the ______
mass-balance expression
Solutions are neutral because the molar concentration of _____ in an electrolyte solution always equals the molar concentration of _____. That is, for any solution containing electrolytes, we may write
no. mol/L positive charge = no. mol/L. negative charge
This equation represents the charge-balance condition and is called the _____. To be useful for equilibrium calculations, equality must be expressed in terms of the molar concentrations of the species that carry a charge in the solution.
Always remember that a charge-balance equation is based on the ______ and that to obtain the charge concentration of an ion, you must multiply the molar concentration of the ion by its ______.
positive charge
negative charge
charge- balance-equation
equality in molar charge concentrations
charge
Figure 5.4 steps for solving problems involving several equilibria
An expression that governs the mass-balance expression and the charge- balance expression, namely, the ______, may be used to solve complex problems.
Takes into consideration only the dominant ion.
For example:
the hydroxide ion in Mg(OH)2
The dominant ion is:
For the weak acid, HA
The dominant ion is:
For the weak base, NH3°H2O, or NH4OH
The dominant ion is
For H2SO4
specific mass-balance expression
H3^-3
H3O^+
H3O^+
H3O^+
All precipitates that contain an anion that is the conjugatc base of a weak acid are more soluble at ___ than at ____ pH.
A ____ keeps the pH of a solution nearly constant
low, high
buffer
_____ occurs naturally in many plants as the potassium or calcium salt, and molds produce oxalic acid as the calcium salt. The _____ is used as a primary standard in redox titrimetry. The acid is widely used in the dye industry as a cleaning agent in a variety of applications, including the cleaning and restoration of wood surfaces, in the ceramics industry, in metallurgy, in the paper industry, and in photography. It is quite poisonous if ingested and may cause severe gastroenteritis or kidney damage. It may be prepared by passing carbon monoxide into concentrated sodium hydroxide.
Oxalic acid
sodium salt
Are frequently performed in buffered solutions in which the pH is fixed at some predetermined and known value.
Analytical precipitations
The solubility of a precipitate always decreases in the presence of a complexing agent that reacts with the cation of the precipitate.
False
increases
In _____, a small excess of precipitating agents minimizes solubility losses, but a large excess often causes increased losses due to complex formation.
gravimetric procedures
Sever precipitating agents permit separation of ions based on solubility differences. Such separations require close control of the active reagent concentration at a suitable and predetermined level.
Most often, such control is achieved by _________.
This method is applicable to anionic reagents in which the anion is the conjugate base of a weak acid.
A well-known example of this technique involves the:
Is a colorless, flammable gas with important chemical and toxicological properties. It is the product of a number of natural processes, including the decay of sulfur-containing organic material. It’s noxious odor of rotten eggs permits its detection at extremely low concentration:(0.02 ppm), but because the olfactory sense is dulled by its action, higher concentrations may be to erated and the lethal concentration of 100 ppm may be exceeded. Aqueous solutions of the gas were used traditionally as a source of sulfide ion for the precipitation of metals, but because of the toxicity of H2S, this role has been taken over by other sulfur-containing compounds such as thioacetamide.
controlling the pH of the solution with suitable buffers
separation of heavy-metal cations by selective precipitation as sulfides
Hydrogen sulfide
A determination using a fluorescent drug and radiation detection is called a
This procedure is repeated for several standard solutions of D to produce a nonlinear working curve called
Fluorescence immunoassay
Dose-responsive curve
