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MCAT Chemistry by me > Solutions and Electrochemistry > Flashcards

Solutions and Electrochemistry Flashcards

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1
Q

solution

A

homogeneous mixture of two or more compounds in a single phase, such as solid, liquid, or gas

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2
Q

solvent

A

in a solution with two compounds, the compound of which there is more

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3
Q

solute

A

the compound of which there is less in a solution

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4
Q

solvation

A

cations and anions of ionic compounds breaking apart and each becoming surrounded by corresponding solvent

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5
Q

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?

A

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

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6
Q

what is an electrolyte

A

a compound that forms ions in aqueous solution

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7
Q

molality

You can use molality to figure out what?

A

moles of solutes divided by kilogram of solvent

You can use molality to figure out the boiling point and freezing point of a solution

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8
Q

What is parts per million?

A

10^6 multiplied by the mass fraction (mass solute/mass solvent)

million times the mass fraction

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9
Q

1 mole of NaCl which dissociates into two parts is dissolved into 1 L of water. What is the molar concentration?

A

1 M

solution concentrations are always given in terms of the form of the solute before dissolution

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10
Q

what is equivalence and normality?

A

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

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11
Q

nitrite

A

NO2-

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12
Q

nitrate

A

NO3-

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13
Q

sulfite

A

SO3-2

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14
Q

sulfate

A

SO4-2

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15
Q

hypochlorite

A

ClO-

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16
Q

chlorite

A

ClO2-

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17
Q

chlorate

A

ClO3-

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18
Q

perchlorate

A

ClO4-

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19
Q

carbonate

A

CO3-2

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20
Q

bicarbonate

A

HCO3-

minus 1

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21
Q

phosphate

A

PO4-3

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22
Q

ammonium

A

NH4+

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23
Q

what is a vapor pressure

A

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

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24
Q

what happens when the vapor pressure equals the local atmospheric pressure

A

the liquid boils

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25
Q

when would a substance evaporate?

A

when the vapor pressure of the liquid phase is greater than the partial pressure in its gaseous phase

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26
Q

what is the effect of velocity on pressure and how does it impact whether or not a substance evaporates?

A

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

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27
Q

when would a substance condense?

A

when the partial pressure of of water vapor is greater than the vapor pressure

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28
Q

what does a solution have lower vapor pressure than a pure solvent?

A

because the non-volatile impurities take up space causing less molecules to break free

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29
Q

effect of increase in pressure on solubility of a gas

A

increase solubility

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30
Q

When could you use Henry’s law?

A

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

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31
Q

when could you use Raoult’s law?

A

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

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32
Q

effect of increasing temperature on solubility of gas

A

decrease

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33
Q

the entropy change when gas dissolves into a liquid

A

negative

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34
Q

effect of size and intermolecular bonds on solubility of gas

A

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

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35
Q

purpose of redox titration

A

to find the molarity of a reducing agent (the one that gets oxidized/lose electrons)

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36
Q

how does redox titration work

A

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

37
Q

in redox titration, when does the equivalence point occur?

A

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

38
Q

what does it mean to have a strong reduction potential? what does it mean when a reduction potential is positive, or negative?

A

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)

39
Q

what is the reduction potential of hydrogen?

A

0 V

40
Q

how to balance redox reactions

A

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

41
Q

When to use nerst equation

What is it

A

Non standard conditions

E = Eo - RT/nF log Q

42
Q

Gibbs free energy of a positive cell potential

A

G = -nFEmax

43
Q

If E is positive G is negative. Then the equilibrium constant is

A

Greater than 1 and vice versa

44
Q

What’s a concentration cell

A

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

45
Q

In a concentration cell, what happens when you add the two half reactions

A

E knot is 0

46
Q

In a concentration cell, where does the electrons flow

A

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

47
Q

What’s an electrolytic cell

A

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

48
Q

Ideal solution

A

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

49
Q

Ideally dilute solution

A

The solutes are so far apart that they don’t interact at all in a solution

50
Q

Non ideal solution

A

Not ideal or ideally dilute

51
Q

Colloid or colloidal suspension

A

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

52
Q

Semi permeable membrane taking out colloidal molecules

A

Dialysis

53
Q

Molarity and temperature

A

Temperature affects molarity bc it changes the volume

Molarity fluctuates with temperature

54
Q

Molality and temperature

A

Molality Moles per mass doesn’t change with temperature

Often used with colligative properties

55
Q

Colligative properties

A

Depends on the number not the type

56
Q

What is the entropy of solution formation?

Positive or negative

A

Always positive

57
Q

Vapor pressure and temperature

A

Increase together

58
Q

Oxidation state rules

A

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

59
Q

in anode and cathode where does oxidation and reduction take place

A

oxidation always take place in the anode and reduction always takes place in the cathode

60
Q

in electrophoresis, the DNA, which is negatively charged, is released into the solution from the _____ toward the _____

A

from the anode toward the positively charged ions

61
Q

direction of current vs the direction of the electron flow

A

opposite

electrons flow from anode to cathode while the current flows in the opposite direction

62
Q

T/F the cell potential for a galvanic cell is always positive

A

true

this means that a galvanic cell always have chemical energy that can be converted to work

63
Q

what determines the real cell potential

A

the half reactions

the concentrations of the reactants and products

the temperature

64
Q

when is the Nernst equation used

A

when it is not at standard condition

65
Q

direction of anions and cations in the salt bridge in respect to electron flow, current, and anode and cathode

A

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

66
Q

what would happen in a galvanic cell without a salt bridge

A

the solutions in the cell would mix, providing a low resistance path for electrons to move from one electrode to another

67
Q

function of salt bridge

A

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

68
Q

how is gibbs free energy related to chemical energy of a cell

what does this gibbs free energy represent?

A

G = -nFE

this gibbs free energy represents the non-PV work that is available to do work at constant pressure and temperature

69
Q

what does positive Emax and negative G represent?

A

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

70
Q

what is the Nernst equation?

A

G = G* + RTlnQ

E = E* - RT/nF log(Q)

at 25C,

E = E* - 0.06/n log(Q)

71
Q

what is special about the concentration cell

A

it is never at standard conditions so the Nernst equation must be used to solve for the cell potential?

72
Q

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?

A

0

the concentration cell potential would be zero

the ion in solution is both a product and a reactant

73
Q

in which direction does the current flow in the concentration cell?

A

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

74
Q

what is the emf of an electrolytic cell?

A

negative

75
Q

what are the signs of cathode and anode for an electrolytic cell?

A

cathode is negative

anode is positive

76
Q

What is characteristic of an ideal solution?

A

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.

77
Q

What is an ideally dilute solution?

A

An ideally dilute solution has very few solutes such that the solutes have no interaction among themselves.

78
Q

How do you measure the heat of solution?

A

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.

79
Q

For which solutions is molality roughly equal to molarity?

A

Dilute solutions at 25˚C.

80
Q

What is the ∆H of an ideal solution?

A

ZERO

81
Q

Solubility vs. Saturation

A

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)

82
Q

What is the equilibrium of Solvation also known as?

A

Saturation point where the solute concentration is at its maximum value for a given temperature and pressure.

83
Q

What does Ksp represent?

A

Maximum concentration of solutes in solution

Rate of precipitation equals the rate of dissolution

84
Q

How is the degree of solubility determined?

A

By the relative ∆H and ∆S associated with dissolution of the ionic solute at a given temperature and pressure.

85
Q

Effect of formation of complex ions in solubility

A

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

86
Q

Common ion effect on solubility

A

Molar solubility (X) decreases but Ksp remains the same

Ksp = ([common ion] + x)*x. But X can be considered negligible.
Ksp = [common ion]*x
87
Q

Boiling point elevation

A

∆T = Kim

M is the molality

88
Q

Freezing point depression

A

∆T = Kim

M is molality

89
Q

Osmotic Pressure

A

Sucking pressure generated by solutions in which water is drawn into a solution

Π = iMRT

MCAT Chemistry by me (8 decks)

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