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Chemistry 2 > Chapter 17 Aqueous Ionic Equilibrium > Flashcards

Chapter 17 Aqueous Ionic Equilibrium Flashcards

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1
Q

Define Buffer

A

A solution that resists pH change by neutralizing the added acid or base

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2
Q

Buffer’s contain significant amount of either…

A

I) A weak acid and its conjugate base

II) A weak base and its conjugate acid

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3
Q

What is a real life example of a Buffer

A

Human blood is a biological buffer in our system

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4
Q

How does a Buffer work if you add a base?

A

Adding a base will be neutralized by the acid

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5
Q

How does a Buffer work if you add an acid?

A

Adding an acid will be neutralized by the base

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6
Q

A Buffer ____________ small to moderate amounts of added ________ or _________ without a ________ __________ in its _____

A

Neutralizes; acid/base; large change; pH

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7
Q

What must a solution contain when making an Acidic/Basic solution?

A

I) Must contain significant amounts of both a weak acid and its conjugate base
II) Most contain significant amounts of both a weak base and its conjugate acid

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8
Q

What are the 2 methods of calculating the pH of Buffer solutions?

A

Method 1: Equilibrium Ice Table

Method 2: Henderson-Hasselbach Equation

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9
Q

Define Henderson-Hasselbach Equation

A

An equation relating the pH of a buffer solution to the initial concentration of the buffer

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10
Q

What is the Henderson-Hasselbach Equation?

A

pH = pKa + log [base]/[acid]

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11
Q

What does pH equal in the Henderson-Hasselbach Equation?

A

pH = pKa when the initial concentrations of the acid and base are equal

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12
Q

T/F For log(x), if x is between more than 0 but less than 1, log(x) will be POSITIVE

A

False; for log(x), if x is between more than 0 but less than 1, log(x) will be NEGATIVE

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13
Q

If x is _________ than 1, log(x) will be ____________

A

Larger; positive

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14
Q

When do you know if Henderson-Hasselbach Equation is good enough to use?

A

Henderson-Hasselbach Equation is good enough to use when “x is small” approximation is applicable

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15
Q

In what 3 circumstances will the “X is small” approximation work?

A

I) Initial acid and conjugate base concentrations are not to DILUTED
II) Equilibrium constant (value of Ka) is fairly small
III) For Buffers: initial concentrations of acids and conjugated bases should be at least 100~1000x greater than Ka

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16
Q

What pH change happens in Buffers when adding OH-?

A

The stoichiometric amount of the weak acid is neutralized and converted to the conjugate base

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17
Q

What pH change happens in Buffers when adding H3O+?

A

The stoichiometric amount of the conjugate base is neutralized and converted to the weak acid

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18
Q

Adding an acid to a buffer = creating more _______

A

Creating more acid

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19
Q

Adding a base to a buffer = creating more _______

A

Creating more base

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20
Q

What equation do you use to find pKa when given pKb?

A

pKa + pKb = 14

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21
Q

Define Buffer Capacity

A

The amount of acid or base a buffer can neutralize

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22
Q

Define Buffer Range

A

The pH range in which the buffer can be effective

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23
Q

Buffer Effectiveness is made up of what?

A

Buffer Capacity and Buffer Range

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24
Q

Buffer effectiveness depends on what 2 factors?

A

I) The relative amounts of buffer acid and base

II) The absolute concentrations of buffer acid and base

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25
Q

Buffer Capacity _________ with __________ absolute concentration of the buffer components

A

Increases; increasing

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26
Q

An __________ buffer neutralizes ________ to ___________ amounts of added acid or base without a _______ _________ in its pH

A

Effective; small; moderate; large change

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27
Q

What are the 2 factors showing when a Buffer is most effective?

A

Factor 1: A buffer is most effective when the concentrations of acid and conjugate base are equal, with a ratio of [base]/[acid] = 1
Factor 2: A buffer is most effective when the concentrations of acid and conjugate bases are high

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28
Q

A buffer will be effective when [base]/[acid] is between what 2 values?

A

0.1 < [base]/[acid] < 10

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29
Q

How do you determine what acid to use when making a Buffer?

A

When choosing an acid to make a buffer, choose the one whose pKa is closest to the pH of the buffer

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30
Q

What is the range used for Buffer Range?

A

0.10 < [base]/[acid] < 10

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31
Q

Effective Buffer Range = ???

A

Effective Buffer Range = pKa + or - 1

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32
Q

What is the Effective Buffer Range equation for lowest pH?

A 
pH = pKa + log[base]/[acid] 
pH = pKa + log0.10 
pH = pKa -1
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33
Q

What is the Effective Buffer Range equation for highest pH?

A 
pH = pKa + log[base]/[acid] 
pH = pKa + log10 
pH = pKa + 1
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34
Q 
A chemist needs a solution buffered at pH 3.30 and has to choose from the following list of acids and their soluble salt, which solution would make the most effective buffer at this pH? 
I) Ka = 2.0x10^-11 
II) Ka = 1.8x10^-5 
III) Ka = 4.5x10^-4 
IV) Ka = 1.7x10^-1 
V) Ka = very large
A 
pKa = -logKa 
I) -log(2.0x10^-11) = 10.69 
II) -log(1.8x10^-5) = 4.74 
III) -log(4.5x10^-4) = 3.35 
IV) -log(1.7x10^-1) = 0.77 
V) -log(100) = -2

Correct Answer: III)

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35
Q 
Which acid would you choose to combine with its sodium salt to make a buffer solution with a pH of 4.25? 
I) HClO2; pKa = 1.95 
II) HNO2; pKa = 3.34 
III) HCHO2; pKa = 3.74 
IV) HClO; pKa = 7.54
A

III)

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36
Q

To create a buffer that maintains a pH around 7.54, which solution would you choose?
I) CH3COOH & NaCH3OO; pKa(CH3COOH) = 4.74
II) HClO & KClO; pKa(HClO) = 7.54
III) NaOH & HCN; pKa(HCN) = 9.31
IV) HNO3 & KNO3; this is a strong acid and salt

A

II)

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37
Q

Define Acid-Base Titration

A

Procedure determining an unknown concentration of a basic (or acidic) solution by reacting with a known concentration of acidic (or basic) solution

38
Q

In an Acid-Base Titration how to you determine the unknown concentration?

A

Unknown concentration determined by precise volumes of acid/base that will completely react

39
Q

Define Indicator

A

A dye whose color depends on pH of solution

40
Q

What does the Acid-Base indicator indicate?

A

Indicates the endpoint of the titration by changing color

41
Q

Define Titration Curve (pH Curve)

A

A plot of the pH of the solution in Erlenmeyer flask (y-axis) and the volume of the solution added (x-axis)

42
Q

Define Equivalence Point

A

The point in the titration when the moles of base is stoichiometrically equal to the moles of the acid

43
Q

BEFORE Equivalence Point what solution is in excess?

A

Solution in Erlenmeyer flask (y-axis) is in excess

44
Q

AFTER Equivalence Point what solution is in excess?

A

Solution from burette is in excess

45
Q

What are the 5 different types of Titration Curves?

A 
I) Adding strong base to a strong acid
II) Adding strong base to a weak acid
III) Adding strong acid to a strong base 
IV) Adding strong acid to a weak base 
V) Titration of a Polyprotic Acid
46
Q

What is the Equivalence Point in the Titration Curve: Adding strong base to a strong acid?

A

Equivalence point: pH = 7

47
Q

Describe the Titration Curve: Adding strong base to a strong acid

A

Before equivalence point starts low from bottom, then pH = 7, then after equivalence point is high at the top

48
Q

What is the Equivalence Point in the Titration Curve: Adding strong base to a weak acid?

A

Equivalence point: pH > 7

49
Q

Describe the Titration Curve: Adding strong base to a weak acid

A

Before equivalence point starts somewhat low, then pH greater than 7, then after equivalence point is high at the top and peaks down

50
Q

What is the Equivalence Point in the Titration Curve: Adding strong acid to a strong base?

A

Equivalence point: pH = 7

51
Q

Describe the Titration Curve: Adding strong acid to a strong base

A

Before equivalence point starts high at the top, then pH = 7, then after equivalence point is somewhat low towards the bottom

52
Q

What is the Equivalence Point in the Titration Curve: Adding strong acid to a weak base?

A

Equivalence point: pH < 7

53
Q

Describe the Titration Curve: Adding strong acid to a weak base?

A

Before equivalence point starts somewhat high peaking down, then pH < 7, then after equivalence point is somewhat low towards the bottom

54
Q

Define Polyprotic Acid

A

Specific acids that pH are capable of losing more than a single proton per molecule in acid-base reactions

55
Q

Polyprotic Acid Titration curves are different from the rest of the Titration Curves how?

A

Polyprotic acid titration curves have 2 equivalence points

56
Q

T/F At Equivalence Point there may not always be equal moles of acids and bases

A

False; at equivalence point there is always equal moles of acids and bases

57
Q

Define Solubility

A

The quantity of the compound that will dissolve in a certain amount of liquid

58
Q

Define Molar Solubility (S)

A

The solubility in units of moles per liter (mol/L)

59
Q

Solubility Product Constant (Ksp)

A

The equilibrium expression for the dissolution of an IONIC COMPOUND (aka salt) into its aqueous ions

60
Q

T/F There are compounds that are completely insoluble

A

False; nothing is COMPLETELY insoluble, just very little of it dissolves

61
Q

Ksp has only ____ value at a given temperature, wheres, solubility can have ____________ values at different kinds of solutions

A

One; different

62
Q

In order to compare the solubility of different compounds by comparing their Ksp values, what must be the same?

A

The compounds must have the SAME DISSOCIATION STOICHIOMETRY

63
Q

The __________ the Ksp value, the _______ solubility

A

Larger; more

64
Q 
Which of the following compounds will have the highest molar solubility in pure water?
I) PbSO4, Ksp = 1.82x10^-8
II) MgCO3, Ksp = 6.82x10^-6 
III) AgCN, Ksp = 5.97x10^-17 
IV) PbS, Ksp = 9.04x10^-29 
V) NiS, Ksp = 3.00x10^-20
A

II)

65
Q

Define Common Ion Effect

A

The tendency for a common ion to decrease the ionization of a weak acid or a weak base or to decrease the solubility of an ionic compound

66
Q

The solubility of an ionic compound is ________ in a solution containing a _________ ion than that in _______ _________

A

Lower; common; pure water

67
Q

What is a good example showing the Ksp equation?

A 
Mx Ny (s) --> xM^y+ (aq) + yN^x- (aq) 
Ksp = [M^y+]^x [N^x-]^y
68
Q

The more the common ions between compounds = ???

A

A reduction in solubility

69
Q

Low pH leads to ______ solubility

A

More

70
Q

High pH leads to ______ solubility

A

Less

71
Q

Define Precipitation Reactions

A

Reactions that occur upon mixing 2 solutions when one of the cross products is insoluble

72
Q

List compounds that are generally soluble with no exceptions

A

Li+, Na+, K+, NH4+, NO3- and C2H3O2-

73
Q

List compounds that are generally soluble except when they are paired with a certain compound. Also identify the compound pair that makes it an exception

A

Cl-, Br- and I- Exception: paired w/ Ag+, Hg2 2+ and Pb2+

SO4 2- Exception: paired w/ Sr2+, Ba2+, Pb2+, Ag+ or Ca2+

74
Q

List compounds that are generally insoluble except when they are paired with a certain compound. Also identify the compound pair that makes it an exception

A 
OH- and S2- 
Exception for both: Li+, Na+, K+ or NH4+ 
Exception for S2-: Ca2+, Sr2+ or Ba2+ 
Exception for OH-: Ca2+, Sr2+ or Ba2+ 
CO3 2- and PO4 3- 
Exception for both: Li+, Na+, K+ or NH4+
75
Q

Ksp is at ___________ only, whereas, Q is under _____ ___________

A

Equilibrium; any condition

76
Q

Explain Q < Ksp

A

Unsaturated, more solid dissolves, NO precipitate forms

77
Q

Explain Q = Ksp

A

Saturated, additional solid does not dissolve, precipitate

78
Q

Explain Q > Ksp

A

Supersaturated, the excess solid precipitates out

79
Q

Define Selective Precipitation

A

The addition of a reagent to a solution containing several cations, forms a precipitate with ONLY ONE of the ions

80
Q

In regards to Selective Precipitation, the ion requires the ___________ amount of added ion precipitates ______

A

Smallest; first

81
Q

Define Complex Ion

A

An ion that contains a central metal ion bound to one or more ligands

82
Q

Define Ligand

A

A neutral molecule or ion that acts as a Lewis Base with the central metal ion

83
Q

Define Complex Ion Formation Reaction

A

The reaction between an ion and ligands to form a complex ion

84
Q

Define Formation Constant (Kf)

A

The equilibrium constant for the formation reaction

85
Q

Large Kf = ???

A

Formation of complex ions is highly favored

86
Q 
Which solution is a buffer? 
I) HNO3 and HCl 
II) HNO3 and NaNO3 
III) NaOH and KCl 
IV) HF and NaF 
V) NH3 and NaOH
A

IV)

87
Q 
Which of the following would be a buffer solution? 
I) 50 mL HCl and 50 mL NaOH 
II) 25 mL NaOH and 50 mL NH3 
III) 25 mL NaOH and 50 mL CH3COOH 
IV) 50 mL HCl and 50 mL NH3
A

III)

88
Q

Consider the titration of HClO with NaOH, determine the pH of the solution at Equivalence Point and the species that determines that pH

A

pH > 7; ClO-

89
Q

What is the dissolution of solid Ca3(PO4)2 in water with a solubility product constant of Ksp?

A

Ca3(PO4)2 –> 3Ca^2+ + 2PO4^3-

90
Q

What is the Ksp expression for Mg3(PO4)2?

A

Ksp = [Mg^2+]^3 [PO4^3-]^2

91
Q

In which solution would BaSO4 be most soluble?
I) 0.10 M BaNO3
II) 0.10 M Na2SO4
III) 0.10 M NaNO3

A

III) B/c it has no common ions

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