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z MCAT: Areas Of Opportunity > Gen Chem > Flashcards

Gen Chem Flashcards

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1
Q

Almost all oxidizing agents contain ______ or another strongly _________ element such as a ________

A

Oxygen; electronegative; halogen

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2
Q

Reducing agents often contain ______ ions or _____

A

Metal; hydrides (H-)

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3
Q

What are some common oxidizing agents?

A 
O2
H2O2
Halogens (F2,Cl2, etc)
H2SO4
HNO3
KMnO4 common in organic chem
CrO3, NaCr2O7 common in organic chem
PCC
NAD+, FAD+ common in biochem
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4
Q

What are some examples of common reducing agents?

A 
CO
C
B2H6
NaBH4
LiAlH4
Hydrazine
Pure metals
Zn(Hg)
NADH, FADH2
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5
Q

Define atomic mass

A

Equal to the mass number, the sum of an elements protons and neutrons

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6
Q

Isotopes have the same number of __________ but differ in the number of __________

A

Protons, but differ in the number of neutrons

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7
Q

The quantum mechanical model posits what?

A

The quantum mechanical model posits that electrons do not travel in defined orbits but rather are localized in orbitals

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8
Q

What is the Heisenberg uncertainty principle?

A

States that it is impossible to know both an electrons position and its momentum exactly at the same time

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9
Q

What are the four quantum numbers and what do they describe in general

A

Principal quantum number (n)
Azimuthal quantum number (l)
Magnetic quantum number(ml)
Spin quantum number (ms)

These numbers completely describe any electron in an atom

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10
Q

What does the principal quantum number (n) describe?

A

The average energy of a shell

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11
Q

What does the azimuthal quantum number (l), describe?

A

Subshells within a given principal energy level (s,p,d, and f)

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12
Q

For any principal quantum number n, there will be n possible values for l, ranging from _______ to ______

A

0 to (n-1)

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13
Q

When l = 0 the sub shell is called ________
When l = 1 the sub shell is called ________
When l = 2 the sub shell is called ________
When l = 3 the subshell is called ________

A

s
p
d
f

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14
Q

The maximum number of electrons within a subshell = ___________

A

4l + 2

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15
Q

T/F: 4s subshell has a lower energy than the 3d subshell

A

True

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16
Q

For any value of l, there will be __________ possible values for ml

A

2l + 1

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17
Q

For any value of n, there will be a maximum of 2n squared electrons ________

A

Two per orbital

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18
Q

What are the two possible values for ms (a quantum number telling spin)

A

+1/2 and -1/2

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19
Q

Whenever two electrons are in the same orbital, they must have ______

A

Opposite spins

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20
Q

n+1 rule can be used to rank subshells by increasing energy. What does this rule state?

A

That the lower the sum of the values of the first and second quantum numbers , n + l, the lower the energy of the subshell

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21
Q

If two subshells possess the same n+l value, the subshell with the lower ______ value has lower energy and will fill with electrons ______

A

n value ; first

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22
Q

What does hunts rule state?

A

Within a given subshell, orbitals are filled such that there are maximum amount of half filled orbitals with parallel spins before pairing up.

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23
Q

Paramagnetic means what?

A

That a magnetic field will cause parallel spins in unpaired electrons and therefore cause an attraction

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24
Q

What are valence electrons?

A

Electrons in the valence shell that are the farthest from the nucleus and have the greatest amount of potential energy

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25
Q

At the atomic level, a metal can be defined by

A 
A low effective nuclear charge
Low electronegativity
Large atomic radius
Small ionic radius
Low ionization energy
Low electron affinity
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26
Q

Nonmetals are periodically defined as

A 
High ionization energies
High electronegativities 
High electron affinities 
Small atomic radii
Large ionic radii
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27
Q

Metalloids are also called ______ because they share some of the characteristics with both metals and nonmetals

A

Semi metals

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28
Q

For elements in the same ______, Zeff(effective nuclear charge) increases from ________ to _______

A

Period; left ; right

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29
Q

As one moves down the elements of a given group, the principal quantum number ______________ each time

A

Increases by 1

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30
Q

How is the Zeff in a given group (family)?

A

It is more or less constant

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31
Q

What are the three key rules that control how valence electrons work in an atom?

A

As one moves from left to right across a periodic table, electrons and protons are added one at a time

As one moves down the elements of a given group, the principal quantum number increases by one each time

Elements also gain or lose electrons in order to achieve a stable octet formation representative of the noble gases.

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32
Q

What is the difference between the atomic radius and the ionic radius?

A

Atomic radius: refers to the size of a neutral element

Ionic radius: is dependent on how the element ionizes based on its element type and group number

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33
Q

_________ is essentially opposite that of all the other periodic trends. While others increase going up and to the right, this one does what?

A

Atomic radius increased going down and to the left

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34
Q

What is ionization potential (ionization energy)

A

The energy required to remove an electron from a gaseous species

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35
Q

The higher the Zeff or the closer the valence electrons are to the nucleus, the _________ the ionization energy is

A

Higher

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36
Q

What is electron affinity?

A

The energy dissipated by a gaseous species when it gains electrons

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37
Q

Electron affinity is an _________ process which means it has a _________ enthalpy (delta H rxn), how ever the electron affinity it reported as a positive number

Ionization energy is an _________ process which means it has a ________ enthalpy

A

Exothermic ; negative

Endothermic; positive

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38
Q

What are the periodic trends that increase from left to right?

A

Ionization energy
Electron affinity
Electronegativity

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39
Q

What are the period trends that decrease from left to right?

A

Atomic radius

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40
Q

What are the periodic trends that increase from top to bottom?

A

Atomic radius

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41
Q

What are the periodic trends that decrease from top to bottom

A

Ionization energy
Electron affinity
Electronegativity

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42
Q

What is the smallest, most electronegative, highest ionization energy, most exothermic (highest electron affinity) element of the periodic table?

A

Fluorine

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43
Q

What element of the periodic table is the largest, least electronegative, lowest ionization energy, and least exothermic (lowest electron affinity)

A

Cesium

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44
Q

What are the characteristics of alkali metals?

A

Typically take on the oxidation state of +1
Prefer to lose an electron to achieve the octet
Most reactive of all metals

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45
Q

C-C

bond length and bond strength

A

Longest bond

Weakest bond

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46
Q

C=C

Bond length and bond strength

A

Medium length

Medium strength

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47
Q

C-triple bond-C

Bond length and bond strength

A

Short length

Strongest bond

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48
Q

7 Naturally occurring diatomic elements

A 
H2
N2
O2
F2
Cl2
Br2
I2
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49
Q

SF6 has what shape and what angle between electron pairs?

A

Shape: octahedral

Angle between electron pairs: 90, 180

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50
Q

PCl5 shape and angle between electron pairs

A

Shape: trigonal bipyramidal

Angle between electron pairs: 90, 120, 180

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51
Q

CH4 shape and angle between electron pairs

A

Tetrahedral

109.5

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52
Q

BH3 shape and angle between electron pairs

A

Trigonal planar

120

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53
Q

BeCl2 shape and angle between electron pairs

A

Linear

180

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54
Q

CH4, NH3, and H2O all have a tetrahedral electronic geometry but differ in their molecular shapes. What are their molecular shapes?

A

CH4: tetrahedral

NH3: Pyramidal

H2O: bent or angular

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55
Q

Hydrogen bonds exist in molecules containing a H bonded to _______, _______, or ________

A

Fluorine, Oxygen, Nitrogen

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56
Q

When the change in electronegativity is less than .5 some bonds can be considered _________

A

Nonpolar

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57
Q

What is a combination reaction?

A

Has two or more reactants forming a product

A+B—-> C

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58
Q

What is a decomposition reaction?

A

A single reactant breaks down into two or more products usually as a result of heating, high-frequency, radiation, or electrolysis

A—–> B+C

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59
Q

What is a combustion reaction? What does it involve? And what are the typical products

A

Involves a fuel (usually a hydrocarbon) and an oxidant (normally oxygen)

CO2 and H2O

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60
Q

What is a single displacement reaction? What are they often further classified by?

A

Occur when an atom or ion in a compound is replaced by an atom or ion of another element

Often further classified as oxidation-reduction reactions

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61
Q

What type of double displacement reaction in which an acid reacts with a base to produce a salt (and usually water

A

Neutralization reaction

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62
Q

Stoichiometry, an application of dimensional analysis is often simplified to a series of 3 fractions. These fractions demonstrate an underlying three step process. What is that process?

A

1) convert from the given units to moles
2) use the mole ratio
3) convert from moles to the desired units

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63
Q

Common conversions of stoichiometry include:
1 mole of any ideal gas at STP= _______
1 mole of any substance =___________ (avagadro’s number)
1 mole of any substance = ____________ (from the periodic table)

A
  1. 4 L
  2. 22x10 23

Its molar mass

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64
Q

What is the limiting reagent?

A

It limits the amount of product that can be formed in the reaction

It is the reactant that is used up or consumed first

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65
Q

When determining the limiting reagent, keep in mind what two principles?

A

1) all comparisons of reactants must be done in units of moles.
2) the rate at which the reactants are consumed, combined with the absolute mole quantities determines which reactant is the limiting reagent

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66
Q

The yield of a reaction can refer to what 2 things?

A

1) the amount of product predicted (theoretical yield)
2) the amount of product actually obtained (raw or actual yield)

When a reaction is carried out

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67
Q

What is the theoretical yield?

A

The maximum amount of product that can be generated as predicted from the balanced equation assuming that:

All of the limiting reactant is consumed
No side reactions have occurred
And the entire product has been collected

** it is rarely ever attained through the actual chemical reaction

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68
Q

What is the actual yield?

A

The amount of product one actually obtains during the reaction

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69
Q

How is the percent yield determined?

A

The ratio of the actual yield to the theoretical yield times 100 percent

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70
Q

Ionic compounds are held together by ionic bonds, which rely on what?

A

The force of electrostatic attraction between oppositely charged particles

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71
Q

Monatomic anions are named by dropping the ending of the name element and adding _____.
Some examples are H-, F-, O2-, S2-, N3-

A

-ide

Hydride, Fluoride, oxide, sulfide, nitride

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72
Q

Many polyatomic ions contain oxygen and are therefore called ________. When an element forms two of these, the name of the one with less oxygen ends in______ and the one with more oxygen ends in ______

Ex: NO2-, NO3-, SO3-2, SO4-2

A

Oxyanions

-ite
Nitrite, sulfite

-ate
Nitrate, sulfate

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73
Q

Hypo- and per- are used to indicate what?

Ex: ClO-, ClO2-, ClO3-, ClO4-

A

Less oxygen and more oxygen

Hypochlorite, Chlorite, Chlorate, Perchlorate

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74
Q

What polyatomic ions have a positive 1 charge?

A

Ammonium

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75
Q

What polyatomic ions have a -1 charge?

A

Acetate C2H3O2

Cyanide CN-

Permanganate MnO4-

Thiocyanate SCN-

76
Q

What polyatomic ions have a -2 charge?

A

Chromate CrO4-2

Dichromate Cr2O7 -2

77
Q

What polyatomic ions have a -3 charge?

A

Borate BO3-3

78
Q

What are the active metals (groups from periodic table) that have charges of +1 and +2 in their natural state?

A

The alkali metals (group 1 or group IA)

The alkaline earth metals (group 2 or group IIA)

79
Q

Alkali metals are not typically found in nature in their uncharged state because ________

Instead they are found as cations in __________

A

They are highly reactive with moisture.

Salts (like NaCl)

80
Q

What compounds make good electrolytes and what makes them good electrolytes?

A

Ionic compounds

Because they dissolve most readily

81
Q

What compound are the weakest electrolytes? And why?

A

Nonpolar covalent compounds because they do not form current-carrying ions.

82
Q

What determines whether or not a reaction is spontaneous or non spontaneous?

A

Gibbs free energy (delta G)

83
Q

The rate of the whole reaction is only as fast as the ______

A

Rate-determining step

84
Q

What is the activation energy?

A

The minimum energy of collision necessary for a rxn to take place

85
Q

_____ activation energy and ______ temperatures make the negative component of the arrhenius equation smaller in magnitude and thus increase the rate constant k

A

Low; high

86
Q

What are the factors that affect reaction rate?

A

Reaction concentrations

Temperature

Medium

Catalysts

87
Q

How does the reaction concentrations affect the reaction rate?

A

The greater the concentrations of the reactants, the greater the number of effective collisions per unit time, which increases the reaction rate for all but zero-order reactions

88
Q

Catalysts only change what in a rxn?

A

The activation energy

89
Q

What are the only factors that can change the rate of a zero-order reaction

A

Temperature and the addition of a catalyst

90
Q

In a zero-order reaction, the rate of formation of product is _________ of the concentration of reactant. And the rate of reaction (k) is _______

A

Independent

Opposite of the slope

91
Q

What is a first order reaction? The rate of formation of product is dependent on ______________

A

Has a rate that is directly proportional to only one reactant

The concentration of reactant

Ln[A] vs time: k= -slope

92
Q

What is a second order reaction?

A

Has a rate that is proportional to either the concentrations of two reactants or the square of the concentrations of a single reactant

1/[A] vs time graph: the k= slope

93
Q

At equillibrium , the rate of the forward rxn equals the rate of the reverse rxn, entropy is at a _______, and Gibbs free energy is at a ________.

A

Maximum; Minimum

94
Q

The law of mass action states what?

A

That if the system is at equillibrium at a constant temperature then the ratio of

Keq =products / reactants with moles as exponent of each

95
Q

In equillibrium the exponents are equal to the ______________

A

Coefficients in the balanced equation

96
Q

In rate laws the exponents must be determined __________________

A

experimentally and often do not equal the stoichiometric coefficients

97
Q

What is the definition of an Arrhenius acid?

A

Will dissociate to form an excess of H+ in solution

98
Q

What is the definition of an Arrhenius base?

A

Will dissociate to form an excess of OH- in solution

99
Q

What is the definition of a Brønsted-Lowry acid?

A

A species that donates hydrogen ions

100
Q

What is the definition of a Brønsted-Lowry base?

A

A species that accepts them

101
Q

Arrhenius definition of acids and bases is limited to what?

A

Aqueous solutions

102
Q

With the Bronsted-Lowry definition of an acid or base, is water an acid or a base?

A

An acid bc it is able to donate a proton to other species

103
Q

What is the Lewis definition of an acid?

A

Lewis acids are electron pair acceptors

104
Q

What is the definition of a Lewis base?

A

An electron pair donor

105
Q

Lewis acid-base chemistry appears in many names and its when one species pushes a lone pair to form a bond with another, what are the names of this type of chemistry?

A

Coordinate covalent bond formation

Complex ion formation

Nucleophile-electrophile interactions

106
Q

What is the definition of an amphoteric species?

A

One that reacts like an acid in a basic environment and like a base in an acidic environment

107
Q

In the bronsted Lowry sense, amphoteric species can__________________

A

Either gain or lose a proton, making it amphiprotic

108
Q

What is the most common example of an amphiprotic species

A

Water.

When water reacts with a base, it behaves as an acid

When water reacts with an acid, it behaves as a base

Other examples are H2SO4 and hydroxides that contain Al, Zn, Pb and Cr. And amino acids

109
Q

What is a proper way of estimating p values on test day?

A

P value= m - 0.n

With n being the exponent (ex 10^6- so n would be 6)

m being the number in front (ex: 1.66X10^-6) 1.66 would be m

110
Q

What is the difference between weak acids or bases and strong acids or bases?

A

Strong acids and bases tend to dissociate completely in aqueous solution.

Weak acids and bases only dissociate partially in aqueous solution

111
Q

The smaller the Ka, _______ the acid and the _______ it will dissociate

A

Weaker ; less

112
Q

The smaller the Kb the _______ the base and the _______ it will dissociate

A

Weaker ; less

113
Q

A species is characterized as a weak acid if its Ka is _________ than 1 and a weak base if its Kb is _________ than 1. Molecular (nonionic weak bases are ____________

A

Almost exclusively amines

114
Q

When is a conjugate acid formed? And when is a conjugate base formed?

A

When a base gains a proton

The base formed when an acid loses a proton

** based on the bronsted-Lowry definition of acid base reactions

115
Q

Ka and Kb are ________ related. If Ka is large, then Kb is ________.

A

Inversely

Small and vice versa

116
Q

When acids and bases react with each other to form a salt and often water what type of reaction is it?

A

A neutralization reaction

117
Q

What is the ground state of an atom?

A

The state of lowest energy, when all of the electrons are in the lowest possible ortbials

118
Q

What is an excited state?

A

When at least one electron has moved to ta subshell of higher than normal energy

119
Q

How can electromagnetic energy of photons be determined?

A

By multiplying planks constant with the speed of light and then dividing that by the wavelength

120
Q

What is a molecule?

A

A combination of two or more atoms held together by covalent bonds

121
Q

What is the basis of equivalents?

A

How many moles are we interested in?

122
Q

What does the gram equivalent weight represent in acid-base chemistry?

A

The mass of acid that yields one mole of OH ions

123
Q

What does the empirical formula give?

A

The simplest whole number ratio of elements in the compound

124
Q

When do isothermal processes occur? And what is temperatures relation to internal energy?

A

When the systems temperture is constant.

Constant temperature implies the total internal energy of the system is constant throughout the process

Temperature and internal energy are directly proportional

125
Q

When does Adiabatic processes occur? How does it appear on a P-V curve?

A

When no heat is exchanged between the system and the environment

The internal energy of the system is constant throughout the process.

The change in internal energy of the system is equal to work done on the system.

Appears hyperbolic on a P-V graph

126
Q

When do isobaric processes occur? How do they change the first law? How do they appear on a P-V graph?

A

When the pressure of the system is constant

They do not alter the first law

As a flat line

127
Q

When do isovolumetric (isochoric) processes occur? How does it affect the first law? How is it represented on a P-V graph/?

A

Experience no change in volume because the gas neither expands no compresses, no work is performed in this process/

The first law is simplified to the change in internal energy is equal to the heat added to the system

As a vertical line on the P-V graph

128
Q

What does a state function describe? What can they not do?

A

The system in an equilibrium state

They cannot describe the process of the system (how the system got to its current equilibrium

129
Q

The pathway taken from one equilibrium state to another is described by process functions. What are the most importna t process functions?

A

Work (W) and Heat (Q)

130
Q

What are examples of state functions? What happens to these when a system changes from equilibrium

A

Pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy

When a state of a system changes from equilibrium, one or more of these states will change

131
Q

What is the ideal gas law? And what does it show a relationship of?

A

PV=nRT

R being the ideal gas constant of 8.21x10^-2 Lxatm/mol.K or 8.314 J/Kxmol

The relationship amoung four variable that define a sample of gas

132
Q

How would one calculate the density of any gas?

A

p=m/V=PM/RT

133
Q

Pressure is ______ to volume

Pressure is ______ to number of moles

Pressure is _____ to temperature

Volume is _____ to temperature

A

Inverse

Proportional

Proportional

Inverse (unless n and P are constant)

134
Q

When temperature what is the ideal gas equation?

A

P1xV1=P2xV2

135
Q

What is the ideal gas equation when moles are constant?

A

P1xV1/T1=P2xV2/T2

136
Q

What are solutions?

A

Homogenous (the same throughout) mixtures of two or more substances that combine to form a single phase, usually the liquid phase

137
Q

What does a solution consist of?

A

A solute dissolved in a solvent.

A solute such as NaCl, NH3, C6H12O2

A Solvent is something like H20 benzene or ethanol

138
Q

What is the definition of a solvent?

A

The component of the solution that remains in the same phase after mixing.

139
Q

What is solvation ?

A

The electrostatic interaction between solute and solvent molecules
AKA a dissolution c

140
Q

When the new interactions are stronger than the original ones, solvation is ________ and the process is favored at _________ temperatures.

A

Exothermic

Low

141
Q

The dissolution of gases into liquids such as ________________ is an ___________ process

A

CO2 into water.

Exothermic s

142
Q

At constant temperature and pressure, entropy always _________ upon dissolution

A

Increases

143
Q

Whether or not dissolution will happen spontaneously depends on what?

A

Both the change in enthalpy and the change in entropy for both the solute and the solvent of the system

144
Q

When the change in Gibbs free energy for the dissolution reaction is neg at a given temperature, the process will be spontaneous and the solute is said to be ________

A

Soluble

145
Q

When the change in Gibbs free energy is postive, the dissolution reaction. Will be nonspontaneous , and the solute is said to be ____________

A

Insoluble

146
Q

Solute are soluble if they have a molar solubility _________ .1M in solution. Those solute that dissolve minimally in the solvent have a molar solubility _______ .1M and are called _______

A

Above

Under

Sparingly soluble salts

147
Q

What do aqueous reactions rely on?

A

The interactions between water molecules and solutes in solutions

148
Q

What are the two absolute solubility rules?

A

All salts of group 1 metals and all nitrate salts are soluble

149
Q

What are coordinate covalent bonds?

A

An electron donor (Lewis base) and an electron acceptor (Lewis acid) form very stable Lewis acid-base adducts.

Ex: proteins utilize this complex ion binding and transition metal complexes to carry out their functions

150
Q

What does the presence of transition metal allows coenzymes and co factors to do?

A

Bind other ligands or assist with electron transfer

151
Q

What is percent composition by mass?

A

Mass of solute divided by mass of solution times 100%

152
Q

What is mole fraction used to calculate and what is the sum of the mole fractions in a system always equal to?

A

Used to calculate the vapor pressure depression of a solution

The sum of the mole fraction in a system will always equal 1

153
Q

What is the molarity of a solution defined as?

A

Moles of solute divided by liters of solution

154
Q

What is molality of a solution defined as?

A

Moles of solute divided by kilograms of solvent

155
Q

What is normality? What is an equivalent?

A

The normality of a solution is equal to the number of equivalents of interest per liter of solution.

An equivalent is equal to a mole of the species of interest. (Protons, OH ions, electrons, or ions)

An equivalent is a measure of the reactive capacity of a molecules

156
Q

When is a solution considered diluted? How is the concentration then determined?

A

When solvent is added to a solution of higher concentration to produce a solution of lower concentration

After dilution the concentration can be determined by molarity times volume (initial) = molarity time volume (final)

157
Q

What is the saturation point?

A

Where the solute concentration is at its maximum value for a given temperature and pressure

158
Q

What is dynamic equillibrium?

A

The rates of dissolution and precipitation are equal and the concentration of dissolved solute reaches a steady-state (constant) value

159
Q

Pure _______ and __________ do not appear in the equillibrium constant

A

Solids and liquids

160
Q

Solubility product constants like all other equillibrium constants are all _________. When the solution consists of a gas dissolved into a liquid the value of the equillibrium constant will also depend on _________

A

Temperature dependent

Pressure

161
Q

How does the solubility product constant differ between non gas solutes and gas solutes when temperature increases?

A

The solubility product constant increases with increasing temperature for non gas solutes and decreases for gas solutes

162
Q

How does ion product indicate that the solution is not yet at equillibrium, and is considered unsaturated? Is dissolution or precipitation more thermodynamically favorable at this time?

A

When a salt’s IP is less than the Salts’ Ksp

Dissolution is thermodynamic favorable

163
Q

When is the solution considered supersaturated? How is a supersaturated solution created?

A

When the Ion product is greater than Ksp then the solution is considered super saturated

By dissolving solute into a hot solvent and then slowly cooling the solution

Precipitation is more thermodynamically favorable

164
Q

When is the solution considered saturated?

A

If the calculate IP is equal to the known Ksp

The solution is in equillibrium

165
Q

What is molar solubility?

A

The molarity of a solute in a saturated solution

166
Q

The dissolution of the of the original solution is termed _____ and the subsequent formation of the complex ion in solution is termed _______

A

Ksp

Kf (the formation or stability constant of the complex in solution)

167
Q

What is the rate limiting step for complex ion formation?

A

The initial dissolution of the metal ion

168
Q

Why do complex ions form?

A

To become more soluble in solution

169
Q

What are colligative properties?

A

Physical properties of solutions that are dependent not he concentration of dissolved particles but not on the chemical identity of the dissolved particles

Ex: vapor pressure depression, freezing point depression, boiling point elevation, and osmotic pressure are usually associated with dilute solutions

170
Q

What is the common ion effect? What effect does it have on the dissociation reaction??

A

It decreases the solubility of a compound in a solution that already contains one of the ions in the compound.

The presence of that ion in solution shifts the dissociation reaction to the left decreasing its dissociation

171
Q

What are pH and pOH of a solution given by?

A

pH= -log[H+] = log 1/[H+}

pOH= -log[OH-] = log 1/[OH-]

172
Q

What is the relationship of pH and pOH

A

As pH increases, pOH decreases by the same amount

An inverse relationship

173
Q

What does a pH greater than 7 or a pOH less than 7 indicate?

What does a pH less than 7 or a pOH greater than 7 indicate?

A

Indicates a relative excess of OH ions and the solution is basic

Indicates a relative excess of H+ ions and the solution is acidic

174
Q

pH is 7 is neutral is applicable only if the temperature is _________

A

25 degrees Celsius or 298K

175
Q

What is an acid equivalent? A base equivalent? And what is polyvalent?

A

Acid equivalent: equal to one mole of H+ (or H30+) ions

Base equivalent: equal to one mole of OH-

Some acids and bases are polyvalent so each mole of the acid or base liberates more than one acid or base equivalent

176
Q

One mole of H2SO4 produces how many acid equivalents?

A

Two (2moles of H3O+)

177
Q

What two measurements are useful for acid-base chemistry?

A

Normality and gram equivalent weight

178
Q

What is gram equivalent weight? What is the gram equivalent weight of H2SO4?

A

The mass of a compound that produces one equivalent (one mole of charge)

H2SO4 has a molar mass of 98 g/mol. It Is a divlaent acid so each mole of the acid compound yields two acid equivalents. The gram equivalent weight is 98/2 = 49 grams.

The complete dissociation of 49 grams of H2SO4 will yield one acid equivalent (1 mole of H3O+)

179
Q

What are the common polyvalent acids? Common polyvalent bases?

A

Common polyvalent acids: H2SO4, H3PO4 and H2CO3

Common polyvalent bases: Al(OH)3, Ca(OH)2, Mg(oH)2

180
Q

How do indicators work in titrations to determine the equivalence point of the acid-base titration ?

A

Indicators are weak organic acids or bases that have different colors in their protonated state and deprotonated states. They need to be weak or else the indicator would be titration first

The point at which the indicator changes to its final color is NOT the equivalence point but rather the ENDPOINT

181
Q

When a strong acid and a strong base are titration the equivalence point of the titration will be what?

A

7 (for monovalent species)

182
Q

What is the equivalence point of a weak acid and strong base titration such as CH3COOH with NaOH.

A

A pH greater than 7

183
Q

What is the difference in titration curves for a strong acid with a strong base compared to a weak acid with a strong base?

A

The PH curve for the strong acid/strong base titration shows a steeper, more sudden rise ath the equivalence point.

In the weak acid/ strong base titration the pH changes more gradually early on in the titration and has less of a sudden rise at the equivalence point

184
Q

What does the pH titration curve look like for a weak base titrand and strong acid titrant ?

A

An inversion of the curve for a weak acid titrand and a strong base titrant

The intial pH will be in the basic range and will demonstrate a gradual drop in pH with the addition of a strong acid

The equivalence point wil be in the acidic pH range

185
Q

With polyvalent acids and bases, when is the equivalence point recognized?

A

There are multiple equivalence points as the H+ ions are removed, a rapid pH change is observed near the equivalence point (the point between regions 4 and 5) as acid is added

z MCAT: Areas Of Opportunity (4 decks)

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