EK chemistry: Chapter 6 solutions and electrochemistry
Group oxidation states
+ 1: Group 1 elements ( alkali metals) + 2: Group 2 elements (alkaline earth metals) +3 Group 15 elements ( nitrogen family) -2 Group 16 elements ( oxygen family) -1 Group 17 elements ( Halogens)
Standard reduction potentials at 25C
- Reactants that are stronger oxidizing agents are more easily reduced. - products that are stronger reducing agents are more easily oxidized,
In which direction will current flow in the concentration cell?
- Remember that nature tends to increase entropy. - Electrons will flow in the direction that allows the concentrations in the half cells to become equal; they will flow toward the side that has greater concentration of positive ions
The general rule for dissolution is that "like dissolved like". This rule refers to the polarity of the solute and solvent.
polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes.
ionic compounds are dissolved by
polar substances.
oxidation states are
possible charge values that an atom can hold within a molecule. - In many cases these charges do not truly exist, and the oxidation state simply provide a system for tracking the movement of electrons.
Since we leave out pure solids and liquids, when a solid dissolves, Ksp includes
products only.
Mass percentage
ratio of the mass of the solute to the total mass of the solution multiplied by 100
The reaction that is more likely reduced will drive the
reaction, and it will get its electrons from the reaction it is coupled with, which becomes an oxidation reaction.
the atom that gains electrons is
reduced
What is mole fraction used for?
to calculate vapor pressure of a solution
In an oxidation-reduction reaction ( also called a redox reaction), electrons are
transferred from one atom to another.
Spectator ions
Ions that are not involved in the overall reaction; -are not included in the equilibrium expression, so they have no effect on the equilibrium
The concentration cell is a particular type of galvanic cell. It is never at standard conditions. So what do we use?
Nernst equation to solve for cell potential E= E0 - 0.06/n log Q * Adding the two half reactions give E0 = 0 . If the concentrations were equal on both sides, the concentration cell potential would be zero.
How cant he potential be found when the concentrations are not one molar?
Nernst equation!
Remember that RED cat. reduction happens at the cathode, so
reduction is the gaining of electrons so electrons must flow to the cathode
The reduction potential of an equation is not an absolute but rather a relative value. Reduction potentials are normally compared to the
reduction of hydrogen.
Half reaction potentials are usually listed as
reduction potentials.
Something that is hydrated is said to be in what phase?
something that is hydrated is said to be in aqueous phase.
reactions in galvanic and concentration cells ( a type of galvanic cells) are always
spontaneous
A nonpolar solute does not have enough separation of charge to interact effectively with a polar solvent so it cannot
spread out within the solvent.
The potentials for oxidation component and reduction component of a reaction can be approximated based on a
standard hydrogen electrode ( SHE)
Highly polar molecules are held together by
strong intermolecular bonds formed by the attraction between their partially charged ends.
Negative heats of solutions are associated with
stronger bonds and lower vapor pressure
If the heat of solution is negative, this means that
stronger bonds are formed and fewer molecules are able to break free from the surface, so there will be a negative deviation of the vapor pressure from Raoult's law
A compound that forms ions in aqueous solution is called an
electrolyte. - Strong electrolytes create solutions that conduct electricity well and contains many ions. - Weak electrolytes form fewer ions in solution.
Since electrons, which have charge, are transferred in a redox reaction, there is an
electron potential ( E) associated with any redox reaction.
A compound will not hand off its electrons unless it is passing them to a
stronger oxidizing agent with a higher reduction potential. * This concept is crucial for the understanding of the electron transport chain, in which electrons are passed along four complexes with increasingly higher reduction potentials.
Compound containing heavier alkaline metals (Ca2+, Sr2+, Ba2+) are soluble when paired with
sulfides (S2-) and hydroxides (OH-)
A volatile solute will also compete for the
surface area of the liquid. However, some of the molecules of a volatile solute will escape from the solution and contribute to the vapor pressure.
Liquid molecules are held in the liquid by intermolecular bonds, but they contain a certain amount of kinetic energy that depends on the
temperature. Some of the liquid molecules at the surface contain enough kinetic energy to break the intermolecular bonds that hold them in the liquid. These molecules break off into the open space above the liquid. As the space above the liquid fills with molecules, some of the molecules crash back into the liquid. *Equilibrium is reached when the rate at which molecules are leaving the liquid equals the rate at which molecules are re-entering the liquid.
A negative cell potential indicates
the cell is electrolytic
A negative heat of solution indicates
the formation of stronger intermolecular bonds.
The more positive the potential
the more likely the reaction is to proceed.
According to the law of conservation of charge,
the oxidation states must add up to the total charge on the molecule or ion. Ex: the oxidation states of the atoms in a neutral molecule must add up to zero.
standard state cell potential
the sum of the standard state potentials of the corresponding half reactions.
A common ion added to a saturated solution shifts the equilibrium, increasing the amount of precipitate. It does NOT affect
the value of Kp.
A compound condenses when
the vapor pressure of its liquid phase is LESS than the partial pressure of its gaseous phase. CL<G
A compound evaporates when
the vapor pressure of its liquid phase is greater than the partial pressure of its gaseous phase. * Its easier to boil water up in the mountain because there is less vapor pressure!!! EL>W
Above the melting point means that
the vapor pressure of the liquid is greater than the vapor pressure of the solid AML>S
Below the melting point means that
the vapor pressure of the liquid is less than the vapor pressure of the solid BMPL<S
Gases that chemically react with a solvent have
greater solubility.
Electrolytic cell need Galvanic cell just
-electrolytic cells need extra energy -galvanic cells just go
Atmospheric pressure is the sum of
all the partial pressures in the air above a liquid.
Imagine a puddle of water on a still day. The puddle is exposed to the open air, so the gas above the puddle is made up of mostly oxygen and nitrogen. However, there is nearly always some moisture in the air. In other words, the air also contains water molecules. Now imagine that the temp of the day is such that the partial pressure of water above the puddle happens to be equal to the vapor pressure of the water. This means that water molecules are entering and leaving the puddle at the same rate. What happens when wind comes along? if the air becomes more moist?
- Wind comes along; The pressure of a fluid decreases as its velocity increases. This means that the partial pressure of the water vapor decreases when the wind blows. The vapor pressure of water does not change, since it is at a given temp. The partial pressure of the water vapor is now LOWER than the vapor pressure of water so WATER ends up EVAPORATING from the puddle. - If the environmental conditions instead made the air more moist so that the partial pressure of the water vapor became GREATER than the vapor pressure, water should CONDENSE into the puddle.
Electrolytic cell
- created by hooking up a power source across the resistance of a galvanic cell and forcing the reactions to run in reverse. - Any electrolytic cell on the MCAT will have a negative emf. - In the electrolytic cell, the cathode is marked negative and the anode is marked positive. - Reduction STILL takes place at Cathode (RED CAT) - oxidation at anode ( AN OX)
Redox titration
- used to find the molarity of a reducing agent To do this, a strong oxidizing agent is titrated and the resulting voltage change is measured. - Voltage is a potential difference. This means that in order to have a voltage our solution must be different from another solution. The other solution is called a standard solution. - When referenced to a standard solution, the solution with the reducing agent has a potential different or voltage. - As the strong oxidizing agent is added to the solution, the voltage increases, at first gradually and then quite suddenly. - Just like in an acid/base titration, there is a half equivalence point where the voltage suddenly shoots up. - As in that process, an indicator must be selected that changes color as close as possible to the expected equivalence point, or the voltage can simply be monitored with a voltmeter. - The equivalence point occurs when all of the moles of reducing agent in the solution have COMPLETELY been oxidized. - The number of moles of oxidizing agent required to reach the equivalence point will be either equal to or a multiple of the number of moles of the reducing agent in the solution that is being titrated. - This is because one molecule of the oxidizing agent may accept a different number of electrons than one molecule of the reducing agent gives up.
Common ion effect
-:involves an ion in "common" with an ion in the equilibrium expression. - According to Le Chatelier's principle, the addition of a common ion pushes the equilibrium in the direction that will reduce the concentration of that ion.
What happens to entropy as solids and liquids dissolve in liquids? What happens as gases dissolve in liquids or solids?
-Entropy usually increases for solids and liquids dissolving in liquids - Entropy usually decreases for gases dissolving in liquids or solids.
cell diagram IUPAC
-Galvanic cells can b represented by cell diagrams -Each phase is listed from left to right, beginning with the terminal attached to the anode and ending with the terminal attached to the cathode. - The terminals are often left out because they are always the same material and do not take part in the reaction. - A vertical line is placed between phases. - A double vertical line indicates a salt bridge - A dotted vertical line indicted a boundary between two miscible liquids, and species in the same phase are separated by a comma - The standard state emf can be found from the cell diagram by subtracting the potential of the reduction half reaction on the left ( at the anode) from the potential of the reduction half reaction on the right ( at the cathode) * you can remember that cathode is at the right because thats where Reduction takes place.
Other factors that affect the solubility of a gas are
-size and reactivity with the solvent
What is the different between solubility and the solubility product (Ksp)?
-solubility product (Ksp) is a constant that can be looked up. - The solubility product is fixed for a given temp - Solubility (S) is the maximum num of moles of a solute that can dissolve in solution. - Solubility depends on both temperature and the ions in solution
In a solution with two compounds, how do you differentiate between the solute and solvent?
-the compound of which there is more is called the solvent - the compound of which there is less is called the solute.
General oxidation state Rules
0: atoms in their elemental form -1: Fluorine +1: hydrogen ( except when bonded to a metal, like NaH;then -1;) -2: oxygen ( except when it is in a peroxide like H2O2; then -1).
Dissolution of salt is reversible: salt particles in solution reattach to the surface of the salt crystal. Steps to reverse dissolution 1. precipitation 2. Saturated
1. At first the rate of the reverse reaction, precipitation, is lower than the rate of dissolution. 2.As the concentration of dissolved salt increases, the rates of dissolution and precipitation equilibrate. At this point, the solution is said to be saturated. In a saturated solution, the concentration of dissolved salt has reached a maximum. Just like the equilibrium established for a chemical reaction, the equilibrium established for saturation is dynamic. The overall concentrations of products and reactants do not change, but the forward and reverse reactions continue to occur at equal rates.
Steps for balancing Redox reactions
1. Divide the reaction into its corresponding half reactions. 2. Balance the elements other than H and O 3. Add H2O to one side until the O atoms are balanced. 4.Add H + to one side until the H atoms are balanced. 5. Add e- to one side until the charge is balanced 6. Multiple each half reaction by an integer so that an equal number of electrons are transferred in each reaction 7. Add the two half reactions and simplify. * For redox reactions occuring in base solution, same steps, then neutralize the H + by adding the same number of OH- ions to both sides of the reaction.
Another factor that can enhance or impair the solubility is the PH of the solution
1. In the presence of base, the excess of hydroxide ions would force the reaction to the left, as predicted by the Le Chatelier's principle. 2. The addition of acid, however, would drive the reaction to the right because H+ would interact with hydroxide ions liberated by dissolution of the compound. Acid removes hydroxide from the solution.
3 keys
1. Increased size or charge tends to decrease solubility. Ksp is the solubility constant- the tendency of a solubility reaction to proceed. S or x is the solubility in water- the concentration that will dissolve 2. In a redox reaction, the species whose reduction potential is more positive is reduced; The other species is oxidized. The potential with the larger magnitude drives the electrochemical reaction 3. In an electrochemical cell, reduction always happens at the cathode and oxidation always happens at the anode. The polarity depends upon the type of cell.
What are the two ways a liquid can be brought to boil?
1. a liquid can be brought to boil by raising the temperature, thereby increasing its vapor pressure until it reaches the atmospheric pressure. 2. Lowering the atmospheric pressure until it equals the vapor pressure.
The formation of a solution is a physical reaction, meaning that the identities of the compounds involved do not change!!! It involves three steps:
1. breaking of the intermolecular bonds between solute molecules 2. breaking of the intermolecular bonds between solvent molecules 3. Formation of the intermolecular bonds between solvent and solute molecules. * Since energy is required to break a bond and is released by the formation of a bond, the first two steps in dissolution are endothermic and the third step is exothermic.
There are five ways you must known to measure the concentration of a solution
1. molarity (M) 2. molality (m) 3. mole fraction (X) 4. mass percentage 5. parts per million (ppm)
Parts per million (ppm)
10^6 multiplied by the ratio of the mass of solute to the total mass of the solution.
Electric potential has no absolute value. The values for standard reduction and oxidation potentials are based on the arbitrary assignment of a zero value to the reduction potential of the half reaction that occurs at a standard hydrogen electrode. Most memorize
2H+ + 2e- --> H2 E0= 0.00V
oxidizing agent
Accepts electrons and becomes reduced.
To remember the direction ions move within the salt bridge
Anions flow toward the Anode and Cations flow toward the Cathode. - Remember the job of the salt bridge is to maintain the neutrality of the half cell. At the anode, as oxidation takes place, positive ions are released into solution. The salt bridge allows anions to migrate so that the charge of the half-cell remains at zero as the cell discharges
Notice that there is no salt bridge in the SHE galvanic cell. WHY?
Both electrodes are in contact with the same solution, so no salt bridge is necessary
The value of all of the following are reversed when a reaction is reversed except A. enthalpy change B. Gibbs free energy charge C. the rate constant D. reaction potential
C. the rate constant Rate constants are dependent on not only temperature but also frequency factor, which accounts for the frequency of favorably oriented collisions, and activation energy. As a result, their magnitudes differ for forward and reverse reactions. * The values of change in enthalpy, change in Gibbs free energy, and reaction potential are all equal in magnitude but opposite in sign for forward and reverse reactions.
galvanic cell
Converts the energy from spontaneous chemical reactions into electricity
Pressure and temp can affect solubility. Pressure has little effect on the solubility of liquids and solids, but it does increase the solubility of a gas. For an ideally dilute solution, the increase in pressure of gas a over a solution is directly proportional to the solubility of gas a. This relationship is described by Henry's Law
C= Ka1Pv where C is the solubility of gas a ( typically in moles per liter), Ka1 is Henry's law constant, which is unique to each solute-solvent pair, and Pv is the vapor partial pressure of gas a above the solution. Henry's law can also be written as: Pv= XaKa2 - Xa is the mole fraction of a in solution, Pv is the vapor partial pressure of gas a above the solution, and Ka2 is Henry's law constant. * Both of the equations show that the concentration of a gas in solution is proportional to the vapor partial pressure of the gas above the solution, but the Henry's law constant in the second equation has a different value than the Henry's law constant in the first equation
hypochlorite
CIO-
Reducing agent
Donates electrons and becomes oxidized.
Nernst equation allows us to plug in nonstandard concentrations to create ! and find the cell potential.
E=E0 - RT/nF ln (Q) At 298K and in base 10 log see pic
If E is positive, then G and K is
G is negative and K >1
If E is negative, the G and K is
G is positive and K<1
In an ideally dilute solution, the solvent obeys Raoult's law and the solute obeys
Henry's law
Raoult's law for nonvolatile solutes
If 97% of the solution is solvent, the vapor pressure will be 97% of the vapor pressure of the pure solvent
Raoult's law for volatile solutes
If 97% of the solution is solvent, the vapor pressure will be 97% of the vapor pressure of the pure solvent PLUS 3% of the vapor pressure of the pure solute.
As temperature increases, gas solubility decreases, the can of soda is useful here as well.
If we place a can of soda on the stove, the gas escapes the solution and expands in the can, causing it to explode. ( THIS IS BECAUSE THE GAS DOES NOT DISSOLVE, SO IT EXPLODES)
Remember the mnemonic
Leo Says Ger lose electrons oxidation gain electrons reduction
Nitrite
NO2- iite
Nitrate
NO3- ate a ThREE
Phosphate
PO4 3-
The sum of the partial vapor pressures is equal to the total vapor pressure of the solution, giving a modified form of the Raoult's law:
Pv = XaPa + XbPb
What happens when ionic compounds dissolve?
SOLVATION!!! When ionic compounds dissolve, the cations and anions break apart and are surrounded by the oppositely charged ends of the polar solvent. Ex: the water molecules around individual ions, point their partially positive hydrogen atoms toward the anions and their partially negative oxygen atoms toward cations.
The components of a simple galvanic cell can be represented by the letters T-E-I-E'-T', where
T represents terminals ( conductors such as metal wires) E represents the electrodes ( also conductors) I represents the ionic conductor ( often the salt-bridge) - When the cell is formed the emf is the electric potential difference between T and T'
The cell potential for a galvanic cell is always positive; a galvanic cell always has
chemical energy that can be converted to work. The real cell potential depends on the half reactions, the concentrations of the reactants and products and the temperature.
The lead storage battery is the cell of choice for cars because of the high current it can supply
The anode is made of lead cathode is made of lead dioxide this battery discharges in the presence of sulfuric acid. The lead anode is oxidized by: Pb(s) --> 2 e- + Pb2+ (aq) The sulfuric acid reacts with the lead ions to precipitate insoluble lead sulfate: Pb2+(aq) + SO42- (aq) --> PbSO4 (s) The cathode of the lead storage battery, in the process of being reduced, also liberates lead ions that interact with sulfuric acid: 2e- + PbO2 (s) + 4H+(aq) + SO42-(aq) --> PbSO4(s) + 2H2O(l) Note that both half reactions produce lead sulfate, an insoluble toxin. To recharge the lead storage battery, a large current is passes through the cell and the reverse half reactions occur. During recharging, the battery behaves as an electrolytic cell, since a large voltage must be applied to make an otherwise unfavorable reaction to proceed
A simple galvanic cell has two electrodes: the anode and the cathode.
The anode is marked with a negative sign and the cathode is marked with a positive sign.
Delta H = Q for
closed systems at constant pressure
Raoult's law
Vapor pressure of solution = mole fraction of solvent * vapor pressure of solvent
Solubility
commonly measured in mol/L, quantifies a solute's tendency to dissolve in a solvent.
Solution
a homogeneous mixture of two or more compounds in a single phase, such as solid, liquid, or gas. - There are solutions in other phases as well. - Brass for instance, is a solid solution of zinc and copper.
When a cell contains two different solutions,
a liquid junction is required to separate the solutions. Because ions can move across a liquid junction, any liquid junction creates an additional small potential difference that affects the potential of the galvanic cell
Remember that Galvanic cells have a positive cell potential and electrolytic cells have
a negative cell potential. - Galvanic cells are spontaneous; - Electrolytic cells are forced by an outside power source.
Volatile solute
a solute with a vapor pressure.
Nonvolatile solute
a solute with no vapor pressure
Salt bridge
a type of liquid junction that minimizes this potential difference Allows the free movement of ions in a voltaic cell
the lead storage battery and the nickel-cadmium battery can both be recharged, so they
alternate between galvanic and electrolytic functions
As shown by raoult's law and Henry's law, the partial vapor pressure of a solution component is
always proportional to its mole fraction. If the component predominates as the solvent, Raoult's law says that the partial vapor pressure is proportional to the pure vapor pressure. If the component represents a tiny amount of solution, Henry's law says that the vapor partial pressure is proportional to Henry's law constant
Sometimes the kidneys experience a buildup of calcium and oxalate ions. Because solubility is maintained in an equilibrium,
an excess ions will push the solubility reaction back towards the sold. Calcium oxalate crystals- otherwise-known as kidney stones-can form as a result.
the oxidation half reaction takes place at the
anode An ox!!!
Nearly all ionic compounds containing nitrate ( NO3-), ammonium (NH4+), and alkali metals ( Li+, Na+, K+...)
are soluble
Main idea: rechargeable commercial batteries behave
as both galvanic and electrolytic cell * A cell phone battery is a galvanic cell when it is in use and an electrolytic cell when its being charged!
Electrons are negatively charged, so they are
attracted to the positive cathode and repelled by the negative anode in a galvanic cell.
When the vapor pressure of a liquid equals the local atmospheric pressure, the liquid
boils.
A polar solute interact strongly with a polar solvent by breaking*** and forming ***
breaking solvent-solvent bonds and forming solvent-solute bonds.
When considering whether a substance is soluble, the question to ask is:
can molecules of solvent surround it?
the reduction half reaction takes place at the
cathode RED CAT
A galvanic cell turns
chemical energy into electrical energy. It's a battery, just like the one that starts your car, powers your cell phone, or energizes your flashlight. - The wire between the anode and cathode is the same kind of circuit as in physics. Any circuit elements would appear there.
At the temperature increases, the solubility of a salt
generally increases.
half cell
container in which oxidation or reduction half reaction occurs
Raoult's law the addition of a nonvolatile solute in a liquid equilibrium solvent results in a
decrease in vapor pressure
In a closed system at constant pressure, the enthalpy change of a reaction equals the heat
delta H = q
When the volatile solute concentration is low, each molecule is surrounded by solvent molecules creating a
deviation from the behavior of pure volatile solute. Its vapor pressure is not proportional to its pressure as a pure substance ( so Raoult's law does not apply) but is proportional to some constant. Henry's law applies.
Polar solutes dissolve in polar solvents and nonpolar solutes dissolve in nonpolar solvents. Because water is polar, it will
dissolve many polar and ionic compounds
With out the salt bridge, the solutions in the cell would mix, providing a low resistance path for electrons to move from Zn(s) to Cu2+ (aq). This would
effectively short circuit the cell, leaving it with a cell potential of zero
the term "electrochemical cell" can mean
either Galvanic or electrolytic cell
When ions form in aqueous solution, the solution is able to conduct
electricity!!!! think of lightening and swimming pool
Half reactions
equations that show either oxidation or reduction alone -No half reaction can occur by itself.
Since the oxidation potential of hydrogen is defined as zero, the cell potential of any electrode used in conjunction with the SHE is
exactly equal to the reduction potential of the half reaction occurring at the other electrode. * Many half reaction reduction potentials can be measured using the SHE
Delta H = delta U
for condensed phases, namely solids or liquids, not a high pressure
Only potential differences between chemically identical forms of matter are easily measurable, so the two terminals of a
galvanic cell must be made of the same material.
As the temperature increases, the solubility of a gas
generally decreases.
Lower energy in the system usually indicates
higher stability
The number of water molecules that must surround an ion for hydration to occur varies according to the size and charge of the ion. This number is called the
hydration number. The hydration number is commonly 4 or 6.
When several water molecules attach to one side of an ionic compound, they can overcome the strong ionic bonds and break apart the compound.The molecules then surround the ion. In water, this is called
hydration.
In an ideal solution, the vapor pressure will be somewhere
in between the vapor pressures of the solute and the solvent, depending on their relative mole fractions.
The strongest oxidizing agent is in the upper left corner of a reduction table. The strongest reducing agent is
in the lower right hand corner of a reduction table. Notice that water is both a poor oxidizing agent and a poor reducing agent. - Notice that the second half reaction is part of the final reaction is aerobic respiration, in which oxygen accepts electrons to form water. Predictably, this reaction has a high positive potential.
Henry's law: Pressure on a gas
increases its solubility
Carbonates, hydroxides, phosphates, and sulfides ( CO32-, OH-, PO43-, S2-) are generally
insoluble other than the cases above
Compounds with water solubilities of less than 0.01 mol/L are generally said to be
insoluble.
If the overall reaction releases heat (is exothermic), the new intermolecular bonds are more stable than the original ones and the
intermolecular attractions within the solution are stronger than the intermolecular attractions within the pure substances.
For condensed phases not at high pressure, which of the case in the formation of most solutions. Enthalpy change approximately equals
internal energy change: deltaD=deltaU. Using these approximations, the heat of solution (DeltaHsol) is given by - Delta H sol = delta H 1 + delta H 2 + delta H 3
A galvanic cell is made of a multiple series of components. No component is present in more than one phase. All phases must conduct electricity, but at least one phase must be impermeable to electrons. Otherwise, electrons would move freely through the circuit and come to a quick equilibrium. The phase that is impermeable to electrons is an
ionic conductor carrying the current in the form of ions.
The cell potential ( E), also called the electromotive force (emf)
is the potential difference between the terminals when they are not connected. * Connecting the terminals reduces the potential difference due to internal resistance within the galvanic cell. The drop in emf increases as the current increases. - the current from one terminal to the other is defined as moving in the direction opposite the electron flow. - Since electrons in the anode have higher potential energy than those in the cathode, electrons flow from anode to cathode.
The more expensive nickel-cadmium battery was an improvement upon the lead storage battery not only because it is less voluminous but also because
its electrolyte is not consumed during discharge. These batteries are arranged in cylindrical configurations that reduced their internal resistance
Compounds containing 2+ cations are
less likely to be soluble
Concentration cell
limited form of a galvanic cell in which a reduction half reaction takes place in one half cell while the exact reverse of that half reaction is taking place in the other half cell. * The cells differ in their ion concentration
Chylomicrons, a class of lipoprotein, enable the transport of fats and cholesterol in the blood by surrounding them within a hydrophilic exteriors. Solubility of these lipoproteins allows
lipids to be transported and distributed by the blood.
However, even in a galvanic cell with a salt bridge, there is some leakage of ions across the liquid junction. This leakage causes the battery to
lose its chemical potential over time.
Parts per million is NOT the number of solute molecules per million molecules. It is the
mass of the solute per mass of solution times one million
Mole fraction is the
moles of a compound divided by the total moles of all species in solution. - since it is a ratio, mole fraction has no units
Molality
moles of solute divided by kilograms of solvent. - usually has units of mol/kg
Molarity
moles of solution divided by the volume of the solution, usually has the units of mol/L.
Typically a salt bridge is made from an aqueous solution of KCl. The salt bridge allows the
movement of ions between solutions without creating a strong extra potential within the galvanic cell. It MINIMIZES the potential because the K+ ions move toward the cathode at about the same rate that the Cl- ions move toward the anode.
A positive cell potential indicates a spontaneous reaction
n is the number of moles of electrons that are transferred in the balanced redox reaction F is the charge on one mole of electrons (96, 486 C mol-1) - This equation says that the free energy represents the product of the total charge nF and the voltage E. - The product of charge and voltage is equal to electrical work, a type of non-PV work. The change in Gibbs free energy represents the maximum non-pV work available from a reaction at constant temperature and pressure. - A negative delta G indicates that work is being done by the system
Notice that the metals used to make coins have
negative oxidation potentials ( except for nickel). * Unlike most metals, plantinum, gold, silver, mercury, and copper do not oxidize ( or dissolve) spontaneously under standard conditions in the presence of aqueous H+.
Since F is a positive constant and n can only be positive, Emax must be positive when delta G is
negative. A positive E max or negative delta G means SPONTANEOUS!
A common ion added to a solution that is not saturated does NOT shift the equilibrium, because in an unsaturated solution, there is
no equilibrium to shift.
What can nonpolar solute break, what can it not break?
nonpolar solute can break weak bonds of nonpolar solvent. Cannot break strong bonds of a polar solvent.
Normality measures the
number of equivalent per liter of solution. - In an acid base reaction, an equivalent is defined as the mass of acid or base that can donate or accept one mole of protons. - A 1 molar solution of H2SO4 is called a 2 normal solution because it can donate 2 protons for each H2SO4 molecule!!!!!!
galvanic cells ( also called a voltaic cell)
offers an alternative pathway for the flow of electrons between phases. The electric potential generates a current from one phase to another in a conversation of chemical energy to electrical energy.
any reduction half reaction must be accompanied by an
oxidation half reaction and vice versa
The atom that loses electrons is
oxidized
Note that the reducing agents and oxidizing agents are compounds, not atoms. In a redox reaction, the atom is
oxidized or reduced; The compound is the oxidizing or reducing agent.
The ionic conducting phase is usually an electrolyte solution in the form of a
salt bridge.
The most important thing to remember about Henry's law is that it demonstrates that the
solubility of a gas is proportional to its vapor partial pressure. We can remember this by thinking of a can of soda. When we open the can and release the pressure, the solubility of the gas decreases, causing some gas to rise out of the solution and create the familiar hiss and foam
The equilibrium of a solvation reaction has its own equilibrium constant called the
solubility products Ksp. Ksp= [concentration of products] / [concentration of reactants], each raised to the power of their coefficient in balanced equations. * remember that solid and pure liquids have an approx mole fraction of one and can be excluded from the equilibrium expression.
Heavier, larger gases experience more van der waal forces and tend to be more
soluble
Sulfate compounds ( SO4 2-) are
soluble, EXCEPT for those containing mercury, lead, and the heavier alkaline earth metals ( Hg2 2+, Pb2+, Ca2+, Sr2+, Ba2+)
Smaller ions or molecules such as those containing GROUP I metals are
soluble, while compounds containing large, heaving cations are less soluble ( as in the case of sulfate compounds that include heavy alkaline earth metals)
Ionic compounds composed of a cation and anion that have a SINGLE positive and negative charge, are usually
soluble.
Ionic compounds containing halogens (Cl-, Br-, I-) are
soluble. EXCEPT for mercury, lead, and silver compounds ( Hg2 2+, Pb2+, Ag+)
When a nonvolatile solute ( a solute with no vapor pressure) is added to a liquid, some
solute molecules reach the surface of the solution and reduce the surface area available for the liquid molecules. - Since solute molecules do not break free from the solution but do take up surface area, the number of molecules breaking free from the liquid decreases while the surface area of the solution and the volume of open space above the solution remain the same. - For this reason, the vapor pressure of a solution is lower than the vapor pressure of the pure solvent.
When do solutions form?
solutions form when the formation of intermolecular bonds between the solvent and solute is more favorable than the intermolecular bonds within the solute and solvent.
When the solvent concentration is high, each solvent molecules is surrounded by other
solvent molecules, so its behaves more like a pure solvent - here the solvent vapor pressure is proportional to its vapor pressure as a pure liquid, and Raoult's law applies.
Imagine a pure liquid in a vacuum-sealed container. The space inside the container above the liquid is not a vacuum. Instead, it contains
vapor molecules that have escaped from the liquid.
The pressure created by the molecules in open space at equilibrium is called the vapor pressure of the liquid. Since vapor pressure is related to kinetic energy of the molecules,
vapor pressure is a function of temperature.
Equilibrium between the liquid and gas phases of a compound occurs when the molecules move from the liquid to the gas as quickly as they move from the gas to the liquid. The partial pressure of the compound that is required to create this equilibrium is called the
vapor pressure of the compound.
Solids also have a vapor pressure. The melting point is the temperature at which the vapor pressure of the solid is equal to the
vapor pressure of the liquid phase of that substance
What holds nonpolar molecules together
weak intermolecular bonds between instantaneous dipole moments. There forces are called London dispersion forces.
Positive heats of solutions are associated with
weaker bonds and higher vapor pressure
A positive heat of solution indicates the formation of
weaker intermolecular bonds.
