acid-base titrations part 3. what does the titration graph tell? if we have a solid that dissolves:...
TRANSCRIPT
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
WEAK BASE WITH STRONG ACID
WEAK BASE WITH STRONG ACID
WEAK BASE WITH STRONG ACID
WEAK BASE WITH STRONG ACID
WEAK BASE WITH STRONG ACID
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.
PRECIPITATION, ION SEPERATION AND KSP
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
PRECIPITATION, ION SEPERATION AND KSP
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
Ions ability to react with water to form H+ ions and OH- ions.
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.
HYDROLYSIS WITH ANIONS
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).
HYDROLYSIS WITH ANIONS
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
Ions ability to react with water to form H+ ions and OH- ions.
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]
RELATIONSHIP BETWEEN KA AND KB
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]
RELATIONSHIP BETWEEN KA AND KB
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]
CALCULATING KA FROM PH
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)
CALCULATING KA FROM PH
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)
CALCULATING PH FROM KA
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
CALCULATING PH FROM KA
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
Seven most common strong acids include six monoprotic acids and one diprotic acid
HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4
STRONG ACIDS
Seven most common strong acids include six monoprotic acids and one diprotic acid
HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4
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)
ION-PRODUCT CONSTANT OF WATER
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)
ION-PRODUCT CONSTANT OF WATER
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-]
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
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)