ACID-BASE TITRATIONS PART 3. WHAT DOES THE TITRATION GRAPH TELL? If we have a solid that dissolves: A 2 B (s) 2 A (aq) + B (aq) Then K sp is calculated

ACID-BASE TITRATIONS

PART 3

WHAT DOES THE TITRATION GRAPH TELL?

If we have a solid that dissolves:

A2B (s) 2 A (aq) + B (aq)

Then Ksp is calculated by Ksp = [A]2 [B] ; at equilibrium (saturation)

STRONG ACID WITH STRONG BASE

WEAK BASE WITH STRONG ACID







GENERIC KSP

If we have a solid that dissolves:

A2B (s) 2 A (aq) + B (aq)

Then Ksp is calculated by Ksp = [A]2 [B] ; at equilibrium (saturation)

GENERAL KSP

Solubility Product of a compound equals the product of the concentration of the ions involved in the equilibrium, each raised to the power of its coefficient in the equilibrium equation.

SOLUBILITY VS. KSP

Solubility of a substance is the quantity that dissolves to form a saturated solution. Usually in g/L or mol/L

Ksp is the equilibrium constant between the

ionic solid and the saturated solution. It has no units and is a measure of how much solid dissolves to form a saturated solution.

SOLUBILITY VS. KSP

Solubility of a substance is the quantity that dissolves to form a saturated solution. Usually in g/L or mol/L

Ksp is the equilibrium constant between the

ionic solid and the saturated solution. It has no units and is a measure of how much solid dissolves to form a saturated solution.

PRECIPITATION, ION SEPERATION AND KSP

What is Q? (Not in terms of James Bond)

Reaction Quotient (Q) : number obtained by substituting reactant and product concentrations (or partial pressures) at any point during a reaction into an equilibrium-constant expression.


What is Q? (Not in terms of James Bond)

a A + b B d D + e E

Q = [D]d [E]e [A]a [B]b


Q and Ksp What do they say?

Q > Ksp Precipitation occurs until Q = Ksp

Q = Ksp at equilibrium (saturated) because Q = Ksp

Q < Ksp solid dissolves until Q = Ksp (think if the solid has not dissolved, then Q is 0 and needs to increase until Q = Ksp

STRONG ACIDS

Seven most common strong acids include six monoprotic acids and one diprotic acid

HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4

STRONG ACIDS

Exist entirely in solution as ions notice the yield sign

HNO3 (aq) + H2O (l) H3O+ (aq) + NO3- (aq)

Or we can state this as:

HNO3 (aq) H+ (aq) + NO3- (aq)

HYDROLYSIS

Ions ability to react with water to form H+ ions and OH- ions.

HYDROLYSIS WITH ANIONS


Look at the anion and see if it is a conjugate base of a strong acid. If yes, the tendency to abstract ions from water is negligible.


If the anion is not a conjugate base of a strong acid, then it is a weak base and would make a weak acid by taking a H+ ion and producing more OH- ions, thereby raising the pH (more basic).


Complicated if anion has ionizable protons, such as H2PO4

-, because it is amphiprotic, act as acid or base.

Look at Ka and Kb of the ion. If Ka>Kb then it causes solution to be acidic. If Ka<Kb then causes solution to be basic.

HYDROLYSIS WITH CATIONS


Polyatomic cation that containing one or more protons (H+) will donate H+ to water to make H3O+

HYDROLYSIS WITH CATIONS

Cations of metals (not alkali and alkaline earth) attract water molecules and become hydrated (remember hydrates) and then cause a water molecule from the hydrate to lose a H+ ion to another water molecule creating a hydronium ion.

ACID STRENGTH

Depends on intermolecular forces.

Polar bonds involving hydrogen allow H to act as proton donor (HCl) or Proton acceptor (NaH)

Strength of bond. HF is so strong to not allow it to be a strong acid.

ACID STRENGTH

Stability of the conjugate base. More stable conjugate bases are found in stronger acids.

Acids with elements in the same group or family show stronger acids as the elements get bigger and bonds get weaker between the element and hydrogen.

ACID STRENGTH

Acidity increases as the electronegativity increases in a period.

OXYACIDS

Acids in which one or more O-H bonds are connected to a central atom (H2SO4)Stronger acids are with similar ions with the same central atom but more oxygens.

ClO- < ClO2- < ClO3

- < ClO4-

CARBOXYLIC ACIDS

Acids which contain a carboxyl group, COOH.

Resonance of COO- allows for stability of conjugate base.

ARRHENIUS ACID- BASE

Acids have Hydrogen ions in solution

Bases have Hydroxide ions in solution

BRØNSTED-LOWRY ACID- BASE

Acids are proton donors

Bases are proton acceptors

LEWIS ACID- BASE

Leweis Acids is an electron pair acceptor

Lewis Bases are an electron pair donor.

Everything already defined as a base (OH-, H2O, amine (N), or anion) are still bases.

LEWIS ACID- BASE

Lewis Bases can also be an electron pair donor to things other than H+

Ex. NH3 + BF3 NH3BF3

Lewis Base Lewis Acid

Electron Pair Acceptor is always referred to as a Lewis Acid if it is not usually called an acid

STRONG ACIDS

Usually a strong acid is the single source of H+ (aq)

HNO3 (aq) H+ (aq) + NO3- (aq)

* If the [acid] is less than 10-6then we need to consider H+ from H2O

STRONG BASES

Seven most common soluble strong bases are the ionic hydroxides of the alkali metals and the ionic hydroxides of the alkaline earth metals

NaOH, LiOH, KOH, etc.Ca(OH)2, Sr(OH)2, Mg(OH)2, etc.

STRONG BASES

Ionic hydroxides of the heavier alkaline earth metalsCa(OH)2, Sr(OH)2, Ba(OH)2, Ra(OH)2

have limited solubility and are used when solubility is not critical

STRONG BASES

Strong basic solutions are also formed by substances that react with water to create OH- Most common substances are oxidesNa2O, CaO, etc. Oxide ion reacts like: O2- (aq) + H2O (l) 2 OH- (aq)

Notice yield sign

WEAK ACIDS

Acids that partially ionize in aqueous solutionsFollow this generic reaction:HA (aq) + H2O (l) H3O+ (aq) + A- (aq)

Equilibrium constant:Kc = [H3O+][A-] = [H+][A-] [HA] [HA]

ACID-DISSOCIATION CONSTANT

Equilibrium Constant to show ionization of an acid (weak acid). Larger Ka indicates stronger acidFollow this generic reaction:HA (aq) + H2O (l) H3O+ (aq) + A- (aq)

Equilibrium constant:Ka = [H3O+][A-] = [H+][A-] [HA] [HA]

WEAK BASES

Bases that react with water and aquire protons, creating conjugate acid and OH-

Follow this generic reaction:B (aq) + H2O (l) BH+ (aq) + OH- (aq)

Equilibrium constant:Kc = [BH+][OH-] = [BH+][OH-] [B] [B]

BASE-DISSOCIATION CONSTANT

Equilibrium Constant to show base reacting with H2O. Larger Ka indicates stronger acidFollow this generic reaction:B (aq) + H2O (l) H3O+ (aq) + A- (aq)

Equilibrium constant:Kb = [BH+][OH-] = [BH+][OH-] [B] [B]

WEAK BASES

Need one or more lone pair of electrons for a H+ to bondTwo categories:Neutral substances with a lone pair of electrons (usually nitrogen, amines)Anions of weak acids are weak bases (ClO- from NaClO)

RELATIONSHIP BETWEEN KA AND KB

Ka x Kb = Kw

NH4+ (aq) + H2O (l) NH3 (aq) + H3O+ (aq)

or: NH4+ (aq) NH3 (aq) + H+ (aq)

and: NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)

Ka = [NH3][H+] Kb = [NH4+][OH-]

[NH4+] [NH3]


When we add the acid and base reactions: NH4

+ (aq) NH3 (aq) + H+ (aq) NH3 (aq) + H2O (l) NH4

+ (aq) + OH- (aq)

H2O (l) H+ (aq) + OH- (aq)Then we multiply equilibrium constants:Ka x Kb = [NH3][H+] x [NH4

+][OH-] [NH4

+] [NH3]


Ka x Kb = [H+][OH-] = Kw SoKa x Kb = Kw

CALCULATING KA FROM PH

0.10 M formic acid (HCOOH) has a pH of 2.38 at 25 °C. What is the Ka?

1st Write reaction:HCOOH (aq) H+(aq) + HCOO+ (aq)To get the Ka = [H+][HCOO-] [HCOOH]


Calculate [H+] from the pH of 2.38 pH = -log [H+] 2.38 = -log [H+] -2.38 = log [H+] 10-2.38 = [H+] 4.2 x 10-3 M = [H+]

EXPRESS CHANGE IN [ ] BY LOOKING AT BCE COEFFICIENTS

Concentrations in M = mol/L

[HCOOH] [H+] [HCOO-]

Initial [ ] 0.10 0 0

Change in [ ] -4.2 x 10-3 4.2 x 10-3 4.2 x 10-3

Equilibrium [ ] 0.10 - 4.2 x 10-3 4.2 x 10-3 4.2 x 10-3

BCE HCOOH (aq) H+ (aq)+ HCOO- (aq)


Since equilibrium concentration for HCOOH is 0.10 – 4.2 x 10-3 we get 0.10 – 0.0042 = 0.10 (with rounding) Ka = [H+][HCOO-] [HCOOH] Ka = (4.2 x 10-3) (4.2 x 10-3) = 1.8 x 10-4

0.10

CALCULATING PH FROM KA

What is pH of 0.30 M acetic acid (HCOOH) at 25 °C?

1st Write reaction:CH3COOH (aq) H+(aq) + CH3COO+ (aq)

To get the Ka = [H+][CH3COO-] [CH3COOH]Ka = 1.8 x 10-5 from a table 16.2 p 667

EXPRESS CHANGE IN [ ] BY LOOKING AT BCE COEFFICIENTS

Concentrations in M = mol/L

[CH3COOH] [H+] [CH3COO-]

Initial [ ] 0.30 0 0

Change in [ ] -x +x +x

Equilibrium [ ] 0.30 -x x x

BCE CH3COOH (aq) H+ (aq)+ CH3COO- (aq)


Ka = [H+][CH3COO-] [CH3COOH] Ka = (x) (x) = 1.8 x 10-4

0.30 - xWe can assume that x is negligible compared to 0.30 since Ka is small and equilibrium should lie to the reactant side


Ka = (x) (x) = 1.8 x 10-4

0.30 x2 = (0.30) (1.8 x 10-4)x2 = 5.4 x 10-6

x = √ 5.4 x 10-6

x = 2.3 x 10-3

[H+] = 2.3 x 10-3 MpH = -log(2.3 x 10-3) = 2.64

PERCENT IONIZATION OF AN ACID

Percent ionization = concentration ionized x 100 % original concentration

Percent ionization = [H+] equilibrium x 100 % [HA] initial

PERCENT IONIZATION OF AN ACID

What is the percent ionization of a 0.035 M solution of HNO2 that cantains 3.7 x 10-3 M H+ (aq)?

Percent ionization = [H+] equilibrium x 100 % [HA] initial

Percent ionization = 3.7 x 10-3 M x 100 % 0.035 M

ION-PRODUCT CONSTANT OF WATER

Kw = [H+][OH-] = 1.0 x 10-14 (25 °C)

If we know the Kw and the concentration of either hydrogen ions or hydroxide ions we can calculate the missing variable

STRONG ACIDS



STRONG ACIDS



LEWIS ACID

Contain H+ in the formula

When dissolved it increases the concentration of hydrogen ions

LEWIS BASE

Contain OH- in the formula

When dissolved it increases the concentration of hydroxide ions

BRONSTED-LOWRY ACID

Acid is a H+ donor

Proton donor

BRONSTED-LOWRY BASE

Base is a H+ acceptor

Proton acceptor

CONJUGATE ACID-BASE PAIR

Acids form a conjugate base when they lose the proton

Bases form a conjugate acid when they gain the proton

RELATIVE STRENGTHS OF ACIDS AND BASES

Strong acids form conjugate bases that have negligible basicity

Weak acids form conjugate bases that are weak bases

Negligible acid in strength form conjugate bases that are strong bases

AUTOIONIZATION OF WATER

Water can act as an acid or a base under the Bronsted-Lowry definition

About 2 out of 109 water molecules ionize at a time.

2 H2O (l) OH- (aq) + H3O+ (aq)


Equilibrium constant for the autoionization of water is:Kc = [H3O+][OH-] = 1.0 x 10-14 (25 °C)

This refers specifically to water so:Kw = [H3O+][OH-] = 1.0 x 10-14 (25 °C)

AUTOIONIZATION OF WATER

Can be written like this in terms of one water molecule

H2O (l) OH- (aq) + H+ (aq)


Equilibrium constant for the autoionization of water is:Kw = [H3O+][OH-] = 1.0 x 10-14 (25 °C)OrKw = [H+][OH-] = 1.0 x 10-14 (25 °C)

[H+] and [H3O+] can be used interchangeably

NEUTRAL

[H+] = [OH-]


Kw = [H+][OH-] = 1.0 x 10-14 (25 °C)

If we know the Kw and the concentration of either hydrogen ions or hydroxide ions we can calculate the missing variable

PH SCALE

Think of pH as the power of H+ :pH = - log[H+] = -log [H3O+]

Example:pH = -log(1.0 x 10-7) = -(-7.00) = 7.00

In a logarithm, the numbers to the right are the only significant figures

POH SCALE

Think of pOH as the power of OH- :pOH = - log[OH-] = -log [OH-]

Example:pOH = -log(1.0 x 10-7) = -(-7.00) = 7.00

In a logarithm, the numbers to the right are the only significant figures

POH SCALE

-log[H+] + (-log[OH-] ) = -log Kw

pH + pOH = 14.00 ( 25 °C)

Documents

ACID-BASE TITRATIONS PART 3. WHAT DOES THE TITRATION GRAPH TELL? If we have a solid that dissolves: A 2 B (s) 2 A (aq) + B (aq) Then K sp is calculated