Chapter 17 Aqueous Ionic Equilibrium Flashcards by Serena Saechia

Define Buffer

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

How well did you know this?

Not at all

Perfectly

Buffer’s contain significant amount of either…

I) A weak acid and its conjugate base

II) A weak base and its conjugate acid

How well did you know this?

Not at all

Perfectly

What is a real life example of a Buffer

Human blood is a biological buffer in our system

How well did you know this?

Not at all

Perfectly

How does a Buffer work if you add a base?

Adding a base will be neutralized by the acid

How well did you know this?

Not at all

Perfectly

How does a Buffer work if you add an acid?

Adding an acid will be neutralized by the base

How well did you know this?

Not at all

Perfectly

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

Neutralizes; acid/base; large change; pH

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

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

Method 1: Equilibrium Ice Table

Method 2: Henderson-Hasselbach Equation

How well did you know this?

Not at all

Perfectly

Define Henderson-Hasselbach Equation

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

How well did you know this?

Not at all

Perfectly

What is the Henderson-Hasselbach Equation?

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

How well did you know this?

Not at all

Perfectly

What does pH equal in the Henderson-Hasselbach Equation?

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

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

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

Larger; positive

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

What pH change happens in Buffers when adding OH-?

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

How well did you know this?

Not at all

Perfectly

What pH change happens in Buffers when adding H3O+?

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

How well did you know this?

Not at all

Perfectly

Adding an acid to a buffer = creating more _______

Creating more acid

How well did you know this?

Not at all

Perfectly

Adding a base to a buffer = creating more _______

Creating more base

How well did you know this?

Not at all

Perfectly

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

pKa + pKb = 14

How well did you know this?

Not at all

Perfectly

Define Buffer Capacity

The amount of acid or base a buffer can neutralize

How well did you know this?

Not at all

Perfectly

Define Buffer Range

The pH range in which the buffer can be effective

How well did you know this?

Not at all

Perfectly

Buffer Effectiveness is made up of what?

Buffer Capacity and Buffer Range

How well did you know this?

Not at all

Perfectly

Buffer effectiveness depends on what 2 factors?

I) The relative amounts of buffer acid and base

II) The absolute concentrations of buffer acid and base

How well did you know this?

Not at all

Perfectly

Buffer Capacity _________ with __________ absolute concentration of the buffer components

Increases; increasing

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

Effective; small; moderate; large change

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

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

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

0.1 < [base]/[acid] < 10

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

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

What is the range used for Buffer Range?

0.10 < [base]/[acid] < 10

Effective Buffer Range = ???

Effective Buffer Range = pKa + or - 1

What is the Effective Buffer Range equation for lowest pH?

``` pH = pKa + log[base]/[acid] pH = pKa + log0.10 pH = pKa -1 ```

What is the Effective Buffer Range equation for highest pH?

``` pH = pKa + log[base]/[acid] pH = pKa + log10 pH = pKa + 1 ```

``` 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 ```

``` 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)

``` 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 ```

III)

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

II)

Define Acid-Base Titration

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

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

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

Define Indicator

A dye whose color depends on pH of solution

What does the Acid-Base indicator indicate?

Indicates the endpoint of the titration by changing color

Define Titration Curve (pH Curve)

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

Define Equivalence Point

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

BEFORE Equivalence Point what solution is in excess?

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

AFTER Equivalence Point what solution is in excess?

Solution from burette is in excess

What are the 5 different types of Titration Curves?

``` 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 ```

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

Equivalence point: pH = 7

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

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

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

Equivalence point: pH > 7

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

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

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

Equivalence point: pH = 7

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

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

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

Equivalence point: pH < 7

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

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

Define Polyprotic Acid

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

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

Polyprotic acid titration curves have 2 equivalence points

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

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

Define Solubility

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

Define Molar Solubility (S)

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

Solubility Product Constant (Ksp)

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

T/F There are compounds that are completely insoluble

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

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

One; different

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

The compounds must have the SAME DISSOCIATION STOICHIOMETRY

The __________ the Ksp value, the _______ solubility

Larger; more

``` 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 ```

II)

Define Common Ion Effect

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

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

Lower; common; pure water

What is a good example showing the Ksp equation?

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

The more the common ions between compounds = ???

A reduction in solubility

Low pH leads to ______ solubility

High pH leads to ______ solubility

Less

Define Precipitation Reactions

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

List compounds that are generally soluble with no exceptions

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

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

Cl-, Br- and I- Exception: paired w/ Ag+, Hg2 2+ and Pb2+ | SO4 2- Exception: paired w/ Sr2+, Ba2+, Pb2+, Ag+ or Ca2+

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

``` 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+ ```

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

Equilibrium; any condition

Explain Q < Ksp

Unsaturated, more solid dissolves, NO precipitate forms

Explain Q = Ksp

Saturated, additional solid does not dissolve, precipitate

Explain Q > Ksp

Supersaturated, the excess solid precipitates out

Define Selective Precipitation

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

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

Smallest; first

Define Complex Ion

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

Define Ligand

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

Define Complex Ion Formation Reaction

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

Define Formation Constant (Kf)

The equilibrium constant for the formation reaction

Large Kf = ???

Formation of complex ions is highly favored

``` 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 ```

IV)

``` 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 ```

III)

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

pH > 7; ClO-

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

Ca3(PO4)2 --> 3Ca^2+ + 2PO4^3-

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

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

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

III) B/c it has no common ions