Exam 2 Activity of Water Flashcards
Keq formula
Keq = ([C][D]) / ([A][B])
pH formula
pH = -log[H+]
Freezing point depression formula
deltaTf = Kf*m
Universal gas law
PV = nRT
T or F: The formula expression are applicable only where ideal behavior is implied i.e. intermolecular, interatomic and/or interionic forces may not be ignored
False; they can be ignored
T or F: Interionic attractive forces between oppositely charged ions of strong electrolytes in solution interfere with movement of these ions
True
T or F: A strong electrolyte may be completely ionized in solution, yet it is incompletely dissociated into free ions
True
T or F: There is interference in the freedom of each of the ions to act towards influencing the freezing point of the solution
True
The ______ of the different ions in solution with each other (or even molecules of the same substance as in the case of solutions of nonelectrolytes) results in a _____ between the experimental value of a certain physical or chemical property and the value calculate using stoichiometric concentration in the mathematical expression
Interference; deviation
It is better to think of the solution as having an effective concentration that is called ______
Activity
Activity, in general, is ___ (more/less) than the actual or stoichiometric concentration of the solute
Less
Chemical or physical property =
f (activity)
An electrode of a pH meter during a pH measurement responds to the _____ of H+, not its concentration
activity
T or F: Since an electrode of a pH meter during a pH measurement responds to the activity of H+, therefore pH = -log(activity H+)
True
Ideal gas law looks at ____ vs. pressure
Fugacity
Activity measures the _____ ______ of a chemical species whether in the state of gas, liquid, or solid, or whether present as a single species or in combination with other species
Net effectiveness
T or F: Activity may be viewed as corrected concentration
True
T or F: Activity takes into account the stoichiometric concentration (or pressure in case of gases) as well as any intramolecular attractions, repulsions, or interactions between solute and solvent in solution, association, and ionization
False; …. as well as any intermolecular (not intramolecular)
T or F: The activities normally used are relative activites
True
T or F: It is possible to assign an absolute value to the activity of a component in solution. Therefore, in order to make quantitative comparisons, a standard state is chosen
True
The ____ state of a component in a solution is the state of the component at unit activity
standard state
The ____ activity of a component is the _____ of activity in an observed state relative to its value in the standard state
relative activity; ratio of activity
T or F: Activity is dimensionless
True
Standard state of a solvent is the pure liquid at ___ atmosphere and at a definite temperature. Therefore, for the pure liquid, a = ___
1; 1
T or F: If the liquid solute isn’t miscible with the solvent, the standard state is the pure solute
False; if the liquid solute is miscible with the solvent
T or F: If a solute has a limited solubility, the standard state is a hypothetical solution of unit concentration under conditions of ideal behavior (the solution has characteristics of an infinitely dilute solution)
True
Activity is a measure of the _____ tendency of a component in the system, which vapor pressure is a component of
Escaping tendency
T or F: Escaping tendency (vapor pressure) is much lower in alcohol vs. water
False; escaping tendency is much lower in water
The separation of one component of a solution from another component by means of pressure exerted on a semipermeable membrane
Reverse osmosis
Most units of reverse osmosis use a _____ _____ membrane which preferentially permits water to pass through over ions and dissolved matter
cellulose acetate
The pores in RO membranes are 5-20 Angstrom units in diameter, which is __-__ cm, and therefore molecules larger than the pores (i.e. with a molecular weight greater than ___) are separated by a simple sieve process
5x10^-8 to 2.5x10^-7
MW > 200
Rejection of salts is as high as ___%, while rejection of most organics is ___%, thus water of extremely high quality can be produced
98%; 100%
T or F: In osmosis, water will flow because of potential energy differences from the less concentrated to the more concentrated solution until the system is in equilibrium
True
T or F: The addition of pressure to the concentrated solution will stop the transport of water across the membrane when the applied pressure equals the apparent osmotic pressure between the two solutions
True
T or F: Apparent osmotic pressure is the difference in the absolute osmotic pressure of each solution. Such a difference is a measurement of the potential energy difference between the two solutions
True
T or F: The absolute osmotic pressure is the potential energy difference between any solution and water
True
T or F: As more pressure is released from the more concentrated side, the water begins to flow from the more concentrated side to the less concentrated side
False; as more pressure is applied to the more concentrated side
At a _____ (static/infinite) dilution, the solute species are separated from each other so far that they do not interact
Infinite
The solution behaves ___ and under these conditions, activity = _____
ideally; activity = concentration
T or F: As the concentration of the solution is increased, the activity/concentration ratio is increased
False: the ratio is decreased
Formula for effective concentration or activity
a = y*m
In the formula a = y*m, y is a correction factor called the
Activity coefficient
The activity coefficient (y) = 1 in ____ solutions, and therefore, activity = concentration
ideal solutions
Which correction coefficient (y) is used for strong electrolytes, and what is the formula?
Strong electrolytes use the correction coefficient of mean ionic activity where (y+/-) = (y+ y-)^0.5
Which correction coefficient is used for ions?
Ionic activity coefficient (yi)
The mean ionic activity coefficients of all electrolytes is 1 at ___ dilution
Infinite dilution
T or F: Mean ionic activity coefficients are expected to equal one at infinite dilution because the solution behaves ideally and (y+/-) is equal to one in the case of ideal solutions
True
Log formula for yi
Look up in notes
Log formula for y+/-
Look up in notes
____ strength is the measure of the intensity of the electrostatic field in a solution due to the presence of ions, and provides a basis for evaluating electrostatic interactions between ions
Ionic strength
T or F: Salts that do not have a common ion with a slightly soluble salt can influence its solubility
True
What are four areas that ionic strength are important in?
Rates of ionic reactions
Solubility of sparingly soluble salts
Effects of salts on pH of buffers
Biological research
