Solutions and Electrochemistry Flashcards
solution
homogeneous mixture of two or more compounds in a single phase, such as solid, liquid, or gas
solvent
in a solution with two compounds, the compound of which there is more
solute
the compound of which there is less in a solution
solvation
cations and anions of ionic compounds breaking apart and each becoming surrounded by corresponding solvent
what is hydration and what phase is it called to be in when a compound is hydrated?
what is hydration number and what is the usual hydration number?
several water molecules surround the ionic part of the compound, and break it apart. This is compound is then called “hydrated”
the number of water molecules that surround this separated ionic part of the compound is called the hydration number which is usually 4 or 6
what is an electrolyte
a compound that forms ions in aqueous solution
molality
You can use molality to figure out what?
moles of solutes divided by kilogram of solvent
You can use molality to figure out the boiling point and freezing point of a solution
What is parts per million?
10^6 multiplied by the mass fraction (mass solute/mass solvent)
million times the mass fraction
1 mole of NaCl which dissociates into two parts is dissolved into 1 L of water. What is the molar concentration?
1 M
solution concentrations are always given in terms of the form of the solute before dissolution
what is equivalence and normality?
equivalent is the “mass” or “moles” of acid or base that can donate or accept one mole of protons in an acid/base reaction
Normality is the number of equivalents per liter of solution.
Reaction dependent, stuff of interest. For example, equivalents may be species of interest like protons, hydroxides, ions, electrons, etc
nitrite
NO2-
nitrate
NO3-
sulfite
SO3-2
sulfate
SO4-2
hypochlorite
ClO-
chlorite
ClO2-
chlorate
ClO3-
perchlorate
ClO4-
carbonate
CO3-2
bicarbonate
HCO3-
minus 1
phosphate
PO4-3
ammonium
NH4+
what is a vapor pressure
pressure created by molecules with enough kinetic energy to break free from the intermolecular bonds keeping the liquid phase at equilibrium**, not influenced by the number of molecules contacting the surface
gas phase coexisting as solid or liquid because it is at an equilibrium. in other words, it is the partial pressure of the compound at equilibrium between different states.
below the critical point so the gas can go back into the liquid just by increasing the pressure without altering the temperature
what happens when the vapor pressure equals the local atmospheric pressure
the liquid boils
when would a substance evaporate?
when the vapor pressure of the liquid phase is greater than the partial pressure in its gaseous phase
what is the effect of velocity on pressure and how does it impact whether or not a substance evaporates?
increase in the velocity, lowers pressure. so if the partial pressure of water vapor is lowered and the vapor pressure becomes greater than the partial pressure of gas, the substance evaporates
when would a substance condense?
when the partial pressure of of water vapor is greater than the vapor pressure
what does a solution have lower vapor pressure than a pure solvent?
because the non-volatile impurities take up space causing less molecules to break free
effect of increase in pressure on solubility of a gas
increase solubility
When could you use Henry’s law?
ideally dilute solution, the solute obeys Henry’s law
Henry’s law is more accurate when it is applied to the vapor partial pressure of a volatile solute where the solute has a low concentration
its vapor pressure is not proportional to its pressure as a pure substance but is proportional to some Henry’s constant
when could you use Raoult’s law?
when the solvent concentration is high so when it behaves more like a pure solvent
the solvent vapor partial pressure is proportional to its vapor pressure as a pure liquid
effect of increasing temperature on solubility of gas
decrease
the entropy change when gas dissolves into a liquid
negative
effect of size and intermolecular bonds on solubility of gas
larger gas molecules have greater van der waals forces and tend to be more soluble
gases that chemically react with a solvent have greater solubility
purpose of redox titration
to find the molarity of a reducing agent (the one that gets oxidized/lose electrons)
how does redox titration work
measuring the potential energy difference but adding a reducing or oxidizing agent.
generally, you add the strong oxidizing agent (gains e) to a strong reducing agent (gives e).
as strong oxidizing agent is added, the voltage increases reaching a half equivalence point where the indicator changes color
in redox titration, when does the equivalence point occur?
when all of the moles of reducing agent in the solution has been completely oxidized
equal to a multiple of the number of moles of the reducing agent in the solution that is being titrated
one molecule of the oxidizing agent may accept a different number of electrons than one molecule of the reducing agent gives up
what does it mean to have a strong reduction potential? what does it mean when a reduction potential is positive, or negative?
accepting electrons readily, more positive the reduction potential, more readily it accepts the electrons (strong oxidizing agent)
more negative the reduction potential, more easily it gives electrons (strong reducing agent)
what is the reduction potential of hydrogen?
0 V
how to balance redox reactions
separate the reaction into halves
balance elements other than O and H first
balance O atoms by adding H2O to one side
balance H atoms by adding H+ to one side
balance e-, multiply each reaction with that integer to balance then add the two reactions
When to use nerst equation
What is it
Non standard conditions
E = Eo - RT/nF log Q
Gibbs free energy of a positive cell potential
G = -nFEmax
If E is positive G is negative. Then the equilibrium constant is
Greater than 1 and vice versa
What’s a concentration cell
Limited form of galvanic cell
A reduction half reaction takes place in one half cell while the exact reverse happens in the other half cell but the cells differ in their Joni concentration
In a concentration cell, what happens when you add the two half reactions
E knot is 0
In a concentration cell, where does the electrons flow
To increase entropy
In a direction that allows the concentrations in the half cells to become equal
Toward the side that has greater concentration of positive ions
What’s an electrolytic cell
Has a power source to run in reverse direction
Has negative emf
Cathode is marked negative and anode is marked positive
Reduction takes place at cathode and oxidation at anode
Ideal solution
The bonds between solute and solution are similar to the bonds between the solutes and between the solvents
The solute and solvent are similar in size and polarity
Ideally dilute solution
The solutes are so far apart that they don’t interact at all in a solution
Non ideal solution
Not ideal or ideally dilute
Colloid or colloidal suspension
Solutes are large molecules or conglomerates of molecules
Gravity gets them to settle out over time
If it doesn’t, the solution is called the colloidal suspension
Causes tindal effect - scattered beams of light
Colloidal particles cannot be extracted by filtration. Heating or adding an electrolyte may cause the particles to coagulate and separated by filtration or settle out by gravity
Semi permeable membrane taking out colloidal molecules
Dialysis
Molarity and temperature
Temperature affects molarity bc it changes the volume
Molarity fluctuates with temperature
Molality and temperature
Molality Moles per mass doesn’t change with temperature
Often used with colligative properties
Colligative properties
Depends on the number not the type
What is the entropy of solution formation?
Positive or negative
Always positive
Vapor pressure and temperature
Increase together
Oxidation state rules
1) Atoms in elemental state have oxidation state of zero
2) hydrogen have +1 unless bonded to a metal which then has -1
3) oxygen has oxidation state of -2
in anode and cathode where does oxidation and reduction take place
oxidation always take place in the anode and reduction always takes place in the cathode
in electrophoresis, the DNA, which is negatively charged, is released into the solution from the _____ toward the _____
from the anode toward the positively charged ions
direction of current vs the direction of the electron flow
opposite
electrons flow from anode to cathode while the current flows in the opposite direction
T/F the cell potential for a galvanic cell is always positive
true
this means that a galvanic cell always have chemical energy that can be converted to work
what determines the real cell potential
the half reactions
the concentrations of the reactants and products
the temperature
when is the Nernst equation used
when it is not at standard condition
direction of anions and cations in the salt bridge in respect to electron flow, current, and anode and cathode
cation in salt bridge: toward cathode, same direction as electron flow, opposite of current,
anion in salt bridge: toward anode, opposite direction of electron flow, same direction as the current
what would happen in a galvanic cell without a salt bridge
the solutions in the cell would mix, providing a low resistance path for electrons to move from one electrode to another
function of salt bridge
allow 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
salt bridge is usually from an aqueous solution of KCl
how is gibbs free energy related to chemical energy of a cell
what does this gibbs free energy represent?
G = -nFE
this gibbs free energy represents the non-PV work that is available to do work at constant pressure and temperature
what does positive Emax and negative G represent?
positive E max shows that the reaction is spontaneous
negative G shows that the reaction is spontaneous and the work is being done by the system
what is the Nernst equation?
G = G* + RTlnQ
E = E* - RT/nF log(Q)
at 25C,
E = E* - 0.06/n log(Q)
what is special about the concentration cell
it is never at standard conditions so the Nernst equation must be used to solve for the cell potential?
what is E* when you add the two half reactions of the concentration cell?
what is the concentration cell potential if the concentrations were equal on both sides?
0
the concentration cell potential would be zero
the ion in solution is both a product and a reactant
in which direction does the current flow in the concentration cell?
in a direction that increases entropy
electrons will flow in the direction that allows the concentrations in the half cells to become equal; they flow toward the side that has a greater concentration of positive ions
what is the emf of an electrolytic cell?
negative
what are the signs of cathode and anode for an electrolytic cell?
cathode is negative
anode is positive
What is characteristic of an ideal solution?
An ideal solution has solutes and solvents that are similar in size. The bonding characteristic of solute-solvent is similar to solute-solute, and solvent-solvent interactions.
What is an ideally dilute solution?
An ideally dilute solution has very few solutes such that the solutes have no interaction among themselves.
How do you measure the heat of solution?
Add the sum of energy needed to break the bonds between solute-solute, solvent-solvent, and the energy released by forming the solute-solvent bond.
For which solutions is molality roughly equal to molarity?
Dilute solutions at 25˚C.
What is the ∆H of an ideal solution?
ZERO
Solubility vs. Saturation
Solubility is the maximum amount of substance that can be dissolved in a particular solvent at a given temperature.
Saturation is the point of solubility when the maximum amount of the substance has been added, and the dissolved solute (surr by solvent) is in equilibrium with its undissolved state. (Dissolved state is in equilibrium with the undissolved state)
What is the equilibrium of Solvation also known as?
Saturation point where the solute concentration is at its maximum value for a given temperature and pressure.
What does Ksp represent?
Maximum concentration of solutes in solution
Rate of precipitation equals the rate of dissolution
How is the degree of solubility determined?
By the relative ∆H and ∆S associated with dissolution of the ionic solute at a given temperature and pressure.
Effect of formation of complex ions in solubility
Increase molar solubility (X) but Ksp remains the same
Rate limiting reaction: Dissolution step
Kf of complex ion formation reaction is very large compared to Ksp of the dissolution step
Common ion effect on solubility
Molar solubility (X) decreases but Ksp remains the same
Ksp = ([common ion] + x)*x. But X can be considered negligible. Ksp = [common ion]*x
Boiling point elevation
∆T = Kim
M is the molality
Freezing point depression
∆T = Kim
M is molality
Osmotic Pressure
Sucking pressure generated by solutions in which water is drawn into a solution
Π = iMRT
