Flashcards in General Chemistry- Solutions Deck (150):
What are solutions?
Homogeneous (the same throughout) mixtures of two or more substances that combine to form a single phase, usually the liquid phase.
What are mixtures?
Gases "dissolved" into other gases can be thought as solutions, but are more properly defined as mixtures because gas molecules do not interact all that much chemically.
Can all solution be considered mixtures? Can all mixtures be considered solutions?
All solution are considered mixtures, but not all mixtures are considered solutions.
What do solutions consist of?
A solute and solvent
What is a solute?
Something dissolved or dispersed in a solvent.
(NaCl, NH3, C6H12O6, CO2)
What is a solvent?
The component of the solution that remains in the same phase after mixing. If the two substances are already in the same phase, the solvent is the component present in greater quantity. If the two same-phase components are in equal proportions in the solution, then the component that is more commonly used as a solvent in other context is considered the solvent.
What do solute molecules do in a solvant?
Move freely in the solvent and interact with it by way of intermolecular forces such as ion-dipole, dipole-dipole, or hydrogen bonding. Dissolved solute molecules are also relatively free to interact with other dissolved molecules of different chemical identities.
What is solvation?
The electrostatic interaction between solute and solvent molecules.
What is another name for solvation?
Dissolution, and when in water Hydration
What is involved in solvation?
Solvation involves breaking intermolecular interactions between solute molecules and between solvent molecules and forming new intermolecular interactions between solute and solvent molecules together.
When is a solvation exothermic?
When the new interactions are stronger than the original ones
What are examples of exothermic processes?
The dissolution of gases into liquids, such as CO2 into water, because the only significant interactions that must be broken are those between water molecules.
What does Le Chatelier's principle tell us?
That lowering the temperature of a liquid favors solubility of a gas in the liquid.
When is a solution endothermic?
When the new interactions are weaker than the original ones
Most dissolutions are exothermic or endothermic?
What are examples of endothermic dissolutions?
Dissolving ammonium nitrate or sugar into water
What must be added to an endothermic dissolution? Why?
Energy must be added because the new interactions between the solute and solvent are weaker than the original interactions between the solute molecules.
What happens when the overall strength of a endothermic solution is equal to the overall strength of the original interaction?
The overall enthalpy change for the dissolution is close to zero. These types of solutions approximate the formation of an ideal solution, for which the enthalpy of dissolution is equal to zero.
What contributes to the sponteneity of dissolution?
Gibbs free energy
What always increases upon dissolution at constant pressure and temperature?
Entropy always increases
Sponteneous processes in dissolution are associated with what in regards to free energy? Nonspontaneous?
Decrease in free energy
Nonspontaneous process with increased free energy
Is the formation of ion-dipole interactions exothermic or endothermic?
Why is the dissolution of table salt in water endothermic?
The magnitude is slightly less than the energy required to break the ionic bonds and hydrogen bonds. As a result the overall dissolution of table salt inot water is endothermic and favored at high temperatures.
What is entropy?
The degree to which energy is dispersed throughout a system or the amount of energy distributed from the system to the surroundings at a given temperature.
What is another way to understand entropy?
The measure of molecular disorder, or the number of energy microstates available to a system at a given temperature.
What does it mean when you say ions have a greater number of energy microstates?
The ions, freed from their lattice arrangement, have a greater number of energy microstates available to them (in simpler terms, they are freer to move around in different ways).
If a solid dissolves in a liquid forming a liquid, what happens to the solid's entropy and what happens to the liquids entropy?
A solid's energy is more distributed and the entropy increases
Liquid becomes more restricted in its movements, microstates decrease and entropy decrease.
How do you determine the overall entropy of a solution?
The increase in the entropy experienced by the dissolved sodium chloride is greater than the decrease in the entropy experienced by the water, so the overall entropy change is positive.
What is solubility?
The maximum amout of that substance that can be dissolved in a particular solvent at a given temperature.
When do we say a solution is saturated?
When the maximum amount of solute has been added, the solution is saturated. If more solute is added, it will not dissolve
What is dilute?
A solution in which the proportion of a solute to solvent is small.
What is concentrated?
The proportion of solute to solvent is large
When are dilute and/or concentrated solutions unsaturated?
If the maximum equilibrium concentration has not yet been reached.
The soluability of substance in different solvants is a function of what?
What happens when the change in Gibbs free energy for a dissolution reaction is negative at a given temperature? What about positive?
The process will be spontaneous and the solute is soluble, if negative.
If positve, The process is nonspontaneous and the solute insoluble.
How do you consider a solute soluable?
If they have a molar solubility above 0.1 M in solution
What are sparingly soluble salts/
Those solutes that dissolve minimally in the solvent (molar solubility under 0.1 M)
What is the most common type of solution?
The aqueous solution
What is an aqueous solution?
The solvent is water
How is the aqueous state denoted?
The symbol (aq)
What is hydration?
The process through which dissolution occurs
In some acid solutions, what complex may form when mixed with water?
Hydronium ion (H30+)
Is H+ ever found alone in solution? Why?
No, because a free proton is difficult to isolate
Why does the MCAT focus on Aqueous solution?
Aqueous solutions are so common and so important to biological systems
What are the seven solubility rules of aqueous solutions?
1. All sals containing ammonium (NH4+) and alkali metal (group 1) cations are water-soluble.
2. All salts contain nitrate (NO3-) and acetate (CH3COO-) anions are water soluble.
3. Halides (Cl-, Br-, I-), excluding fluorides, are water-soluble, with the exception of those formed with Ag+, Pb 2+ and Hg2 2+
4. All salts of the sulfacte ion (SO4 2-) are water soluble, with the exceptions of those formed with Ca 2+, Sr 2+, Ba 2+, and Pb 2+
5. All metal oxides are insoluble, with the exception of those formed with alkali metals, ammonium, and CaO, SrO, and BaO, all of which hydrolyze to form solutions of the corresponding metal hydroxides.
6. All hydroxides are insoluble, with the exception of those formed with alkali metals, ammonium, and Ca 2+, Sr 2+, Ba 2+.
7. All carbonates (CO3 2-), phosphates (PO4 3-), sulfides (S 2-), and sulfites (SO3 2-) are insoluble, with the exception of those formed with the alkali metals and ammonium.
What are the two absolute rules of solubility in aqueous solutions you should know on the MCAT?
All salts of Group 1 metals, and all nitrate salts are soluble.
What are usually used as counter ions?
Sodium and nitrate ions are generally used as counterions to what is actually chemically important
When is the only time you should worry about nitrate ion concentration as a chemically reacting species? Otherwise just focus on what?
In an oxidation-reduction reaction, for the nitrates ion to function, weakly, as a oxidizing agent.
Otherwise just focus on the cation as the chemically reacting species.
What is a complex ion?
A molecule in which a cation is bonded to at least one electron pair donor (which could include the water molecule).
What is another name for complex ion?
What are ligands?
The electron pair donor molecules.
What is an example of a complexation reaction?
The tetraaquadioxouranyl cation, which has water (aqua-) and oxygen (oxo-) ligands.
How are complexes held together?
Coordinate covalent bonds
What are coordinate covalent bonds?
An electron pair donor (a Lewis base) and an electron pair acceptor (a Lewis acid) form a very stable Lewis acid-base adducts.
What biologically uses complex ion bonding?
Many active sites of proteins utilize complex ion binding and transition metal complexes to carry out their function.
What is an example of complex ion binding biologically?
The iron cation in hemoglobin, which can carry oxygen carbon dioxide, and carbon monixde as ligands
What else contains complexes of transition metals?
Many coenzymes (vitamins) and cofactors also contain complexes of transition metals.
What is an example of a coenzymes/cofactor?
Cobalamin (vitamin B12)
What does the presence of a trantion metal allow in coenzymes and cofactors?
Bind other ligands or assist with electron transfer.
What is chelation?
In some complexes, the central cation can be bonded to the same ligand in multiple places.
What is required for chelation?
Large organic ligands that can double back to form a second (or even a thrid) bond with the central cation.
When is chelation therapy used?
To sequester toxic metals (lead, arsenic, mercury, and so on). Even biologically necessary metals such as iron can be toxic in overload states.
What is concentration?
The amount of solute dissolved in a solvent.
How are concentrations commonly expressed on the MCAT?
As percent composition by mass, mole fraction , molality, and normality.
What is the equation for the parent composition by mass?
Mass of solute/mass of solution X 100%
When is percent composition used?
For aqueous solutions, and for metal alloys and other solid-in-solid solutions.
What is the equation for mole fraction?
Xa= Moles of A/ Total moles of all species.
When is the mole fraction used?
To calculate the vapor pressure depression of a solution, as well as the partial pressures of gases in a system
What is the equation for molarity?
M= Moles of solute/ liters of solution
What is the most common concentration equation on the MCAT?
When is molarity equation usually used?
What symbolizes molarity?
Brackets indicate molarity
In the molarity equation, what is meant by the volume term in the denominator?
The solution volume, no the volume of solvent used to prepare the solution
What is the equation for Molality?
m= moles of solute/kilograms of solvent
For dilute aqueous solutions at 25 degrees Celsius, What is important to know about molality and molarity? Why?
They are equal. Because the density of water at this temp. is 1 kilogram per liter.
Is the equality of molarity and molality true for all aqueous solutions?
No, true only for dilute aqueous solutions.
When is molality used?
Boiling point elevation and freezing point depresion.
What is the normality of a solution?
(N) is equal to the number of equivalents of interest per liter of solution.
What is an equivalent?
A measure of the reactive capacity of a molecule. Most simply, an equivalent s equal to a mole of the species of interest -- protons, hydroxide ions, electrons, or ions.
How do you calculate the normality of a solution?
You need to know what purpose the solution serves because it is the concentration of the reactive species with which we are concerned.
For acid-base reactions, what aspect is important to calculate normality?
The concentration fo hydrogen ions.
For oxidation-reduction reactions, what aspect is important to calculate normality?
The concentration of electrons.
When is a solution diluted?
When solvent is added to a solution of higher concentration to produce a solution of lower concentration.
How do you calculate the concentration of a solution after dilution?
What do the letters represent in the equation to calculate concentration after dilution?
M is molarity
V is volume
The subscripts i and f refer to inition and final values.
What is the saturation point?
The equilibrium when creating a solution
What happens immediately after a solute has been introduced into a solvent?
Most of the change taking place is dissociation because no dissolved solute is initially present.
What happens when the solute dissolves in the solvent after the initial introduction?
The reverse proccess-percipitation of the solute- will happen
When the solution is dilute, what is the thermodynamically favored process?
Dissolution, and initially, the rate of dissolution will be freater than the rate of precipitation
When the solution is more concentrated, what is the thermodynamically favored process?
Precipitation increases and dissolution lessens
What happens once the solution has reached the saturation point?
The solution exists in a state of dynamic equillibirum for which the rate of dissolution and precipitation are equal, and the concentration of dissolved solute reaches a steady-state (constant) value. Neither dissolution nor precipitation is more thermodynamically favored at equilibirum.
What happens when an ionic solid is introduced into a polor solvent? How is it represented?
Dissociates into its component ions.
A(m)B(n) (solid) m A ^n+ (aq) + n B^ m- (aq)
What is the essential first step to do on the MCAT, dealing with solutions, for a chemistry problem? Why?
Write out the balanced dissociation reaction for the ionic compound in equation.
The first step is essential for correctly calculating the solubility product constant, ion product, molar soubility, or for determining the outcome of the common ion effect.
What determines the solubility of an ionic solute?
The relative changes in enthalpy and entropy associated with the dissolution of the ionic solute at a given temperature and pressure.
What is an example of a sparingly soluble salt?
Silver chloride, AgCl, which dissociates in water.
AgCl (s) Ag+ (aq) + Cl- (aq)
What is the equilibirum constant for a saturated solution of an ionic compound with the formula AmBn?
Ksp= [A^n+]^m [B^m-]^n
What does ksp stand for?
Solubility product constant
Do ksp expression have denominators? Why?
Never. They have a solid salt reactant
What are soluability product constant dependent on?
Also, when the solution consists of a gas dissolved in a liquid, the value of the equilibirum constant, will depend on pressure too.
Generally speaking, solubility prodct constants increase with what? Decrease with what?
Increases with increasing temperature for non-gas solutes and decreases for gas solutes.
Higher pressure favor dissolution of gas solutes, and therefore Ksp will be larger for gases at higher pressures than at lower ones.
Why do you calculate the ion product?
To know when solution has reached saturation, and determine where the system is with respect to the equilibrium position.
What is another name for ion product?
Reaction quotient, Q
What is the difference between the solubility prodcut constant and the ion product if they both have the form IP = [A^n+]^m [B^m-]^n
The concentrations used in the ion product equation are the concentrations of the ionic consituents at that given moment in time, which may differ from equilibrium concentrations. The utility of the ion produt lies in comparing its value to that attained at equilibrium.
If, at a given set of conditions, a salt's IP is less then the salt's Ksp at a given temperature, what does it mean?
The solution is not yet at equilibrium, it is unsaturated.
For unsaturated solutions, what thermodynamically is favored?
If the IP is greater then the Ksp, what does it mean?
The solution is beyond equilibrium, it is supersaturated.
How do you create a supersaturated solution?
By dissolving solute into a hot solvent and then slowly cooling the solution.
Thermodynamically, what is a supersaturated solution? What will happen?
Unstable, and any disturbance to the solution, such as addition of more solid solute or other solid particles, or further cooling of the solution, will cause spontaneous precipitation of the excess dissolved solute.
What does it mean when the IP is equal to the Ksp?
The solution is at equilibrium and the solution is considered saturated.
What is molar solubility?
The molarity of a solute in a saturated solution
What determines the solubility of a complex ion?
By the Ksp
What increases the solubility of a salt in solution?
The formation of complex ions
When forming a complex ion, what often is used?
Mixture of solution.
How can you differentiate the Ksp and the mixture for the complex ion?
The dissolution of the original solution is Ksp
The subsequent formation of the complex ion in solution is Kf (the formation or stability constant of the complex in solution)
Is the Kf or the Ksp usually larger?
Why do complex ions form?
To become more soluble in solution
Solubility varies depending on what?
The temperature of the solution
The case of gas-phase solute
Addition of other substances
Is the effect of a complex ion typical in the solubility of a substance?
No, it is opposite to the effect seen in many mixtures because it increases the solubility of a substance.
What is the common ion effect?
The equilibrium concentration of a salt in a solution athat already contains one of the ions in the salt. The solubility of a salt is considerably reduced when it is dissolved in a solution that already contains one of the constituent ions as compared to its solubility in a pure solvent. The reduction in molar solubility is the common ion effect.
What is the molar solubility of a compound?
Its concentration (in moles per liter) at equilibrium at a given temperature. If x moles of AmBn (s) can be dissolved in one liter of solution to reach saturation, then the molar solubility of AmBn (s) X molar.
What is the effect of adding a common ion to a solution?
Its presence results in a reduction in the molar solubility of the salt.
What is important to note when dealing with the common ion effect?
No effect on the value of the solubility product constant itself.
The common ion effect is which principle in action? Why?
Le Chatelier's principle. Because the solution already contains one of the constituent ions from the products side of the dissociation equilibrium, the system will shift toward the left side, reforming the solid salt.
What results due to the common ion effect?
Molar solubility for the solid is reduced, and the less of the solid dissolves in the solution-- although the Ksp remains constant.
What can the common ion effect be used for?
To separate out specific compounds in a solution mixture
What are colligative properties?
Physical properties of solutions that are dependent on the concentration of dissolved particles but not on the chemical identity of the dissolved particles.
Whatare examples of colligative properties?
Vapor pressure depression, boiling point elevation, freezing point depression, and oxmotic pressure.
What are colligative properties usually associated with/
What does Raoult's Law account for?
Vapor pressure depression caused by solutes in solution.
What happens to the vapor pressure of the solvent as solute is added to it?
The vapor pressure of the solvent decreases proportionately
On the molecular level, what happens to the vapor pressure as solute is added to solvent?
The presence of solute molecules can block the evaporation of the solvent molecules but not their condensation. This reduces the vapor pressure of the solution compared to the pure solvent.
How is Raolt's Law expressed mathmatically?
Pa= (Xa)(P degree a)
What do the letter represent in Raolt's Law?
Pa: vapor pressure of solvent A when solutes are present
Xa: the mole fraction of the solvent A in the solution
P degree a: the vapor pressure of solvent A in its pure state
Raolt's Law only holds true when?
The attraction between the molecules of the different components of the mixture is equal to the attraction between the molecules of any one component in tis pure state.
What solutions obey Raolt's Law?
What happens when a nonvolatile solute is dissolved into a solvent to create a solution?
The boiling point of the solution will be greater than that of the pure solvent.
What is boiling point?
The temperature at which the vapor pressure of the liquid equals the ambient (incident) pressure.
Why is the boiling point greater when a nonvolatile solute is dissolved into a solvent to make a solution?
The vapor pressure decreases, and if it is lower than that of the pure solvent, then more energy ( and a higher temperature) will be required before its vapor pressure equals the ambient pressure.
What is the equation that shows boiling point having raised compared to a pure solvent?
What do the letters represent in the equation for boiling point elevation?
/\(Tb): Increase in boiling point
i: the van't Hoff factor
Kb: a proportionality constant characteristic of a particular solvent
m: molality of the solution.
What is the Van't Hoff factor?
The number of particles into which a compound dissociates in solution.
Explain freezing point depression?
The presence of solute particles in a solution interferes with the formation of the lattice arrangement of solvent moleucles associated with the solid state. Thus, a greater amount of energy must be removed from the solution (resulting in a lower temperature) in order for the solution to solidify.
What is the equation for freezing point depression?
What do the letters mean in the freezing point depression equation?
/\Tf: Freezing point depression
i: Van't Hoff factor
Kf: The proptionality constant characteristic of a particular solvent
What type of property is freezing point depression?
A colligative property and dpends on ly on the concentration of particles, not on their identies.
What is osmotic pressure?
A sucking pressure generated by solutions in which water is drawn into a solution. Formally, the osmotic pressure is the amount of pressure that must be applied to counteract this attraction of water molecules for the solution.
What is the equation for osmotic pressure?
What do the letters represent for the equation for osmotic pressure?
II: osmotic pressure
i: van't Hoff factor
R: the ideal gas constant
Water moves in the direction of higher what?