Acids, Bases & Salts....Oh my!

AP Chemistry, Mr. Guerrero

Acids:Sour tasteTurn litmus redElectrolytes- form ions in waterCorrosive-cause chemical burns to skinReact w/ metals to produce salt and H2 gas

HX + M MX + H2(g) (S. Repl. Rxn)Acids neutralize bases to make salt + waterComplete and balance each neutralization rnx:

HClO3 + Mg(OH)2 KOH + H3PO4

Acids-have 3 definitions

Arrhenius Acid-Any substance which release H+ ions in water.

Rxn: HA H+ + H2O A- + H3O+

(acid) (conjugate base) (hydronium ion)

Bronsted-Lowry Acid- a proton(H+) donor.Rxn: HA H+ + A-

(ACID) (Proton) (Conjugate Base)

Lewis Acid- an e- pair acceptor.(mostly in bonding)Rxn: X + :Y X--Y

Acids-covalent compounds that have H+ cations and ionize(dissociate) in water.

Monoprotic acids- dissociate only one proton.ex: HCl, HCN, HClO3

Diprotic acids- dissociate two protons.ex: H2SO4, H2CO3, H2C2O4

Triprotic acids- dissociate three protons.ex: H3PO4

Organic(carboxylic) acids: All are weak acidsRCOOH RCOO- + H+

Write the dissociation rxn for each acid:• HCN• HNO2

• H2CO3

• CH3COOH

• H3PO4

• NH4+

• HClO4

Amphoteric molecule- a subtance that can act as either an acid(donate H+) or a base(accept a H+).

• Conjugate base of a weak acid

• water

Strong Acid- any acid that has 100 % dissociation in water

There are only 6 strong acids-HCl hydrochloric acid(muriatic acid or stomach acid)HBr hydrobromic acid(mostly in scientific research)HI hydroiodic acid(illegal to possess)HClO4 perchloric acid(strongest of all)HNO3 nitric acid(fertilizers, explosives)H2SO4 sulfuric acid(battery acid, most produced

chemical world-wide)

Oxyacid strength-the more O’s the stronger the acid.

How much more acidic is lemon juice than tomato juice?

[H+] > [OH-] [H+] = [OH-] [H+] < [OH-]

pH Equations

pH = - log [H+] (14-) Kw/known

pOH = - log [OH-]

pH + pOH = 14 [H+]x[OH-] = Kw = 1 x 10-14

Find the pH of the following solutions: 0.025 M HCl

0.085M HNO3

0.045M HCl

Weak acids-molecules with usually less than 5% dissociation

Find the pH of a 0.50 M HC2H3O2(acetic acid) solution(Ka = 1.8 x 10-5)

R .IC .E (find % diss.)Write out equilibrium expression:Ka =

Find the pH of a 0.750 M HNO2 solution(Ka = 5.1 x 10-4)

Bases

Bitter tasteTurn litmus blueDissolve protein(feel slippery)Release ions in water(ions)CorrosiveNeutralize Acids

Definitions of Bases• Arrhenius Base-any substance which releases OH-

(hydroxide ions) in water.• Ex: MOH M(aq)

+ + OH-(aq)

(metal hydroxide) (metal cation) (hydroxide ion)

Bronsted-Lowry Base-a proton acceptor!!!!Ex: BHx + H+ BHX+1

This is the first time amine chemistry is finally explained!Amines: NHx + H+ NH+

x+1

Lewis Base: e- pair acceptor:X + :Y X—Y LA LB (Coordinate Cov. Bond)

8 strong(soluble) bases-They are all Arrhenius acids:

• LiOH• NaOH• KOH• RbOH• CsOH• Ca(OH)2

• Sr(OH)2

• Ba(OH)2

Find the pH of each strong Arrhenius base solution:

• 0.0044 M NaOH

• 0.075 M Ba(OH)2

• 0.010M KOH

Most bases are weak amines.

Find the pH of 0.250 M NH3 solution(Kb = 1.8 X10-5)R ICE

Kb = _________

Find the pH of 0.0500M C5H5N(pyridine)

R ICE

Kb = _________

Find the pH of a 1.20M CH3NH2, methylamine solution, Kb = 4.38 x 10-4

RICE

Kb = _________

Polyprotic acids: Find the pH of a 3.0M H3PO4 solutionKa1 = 7.5 x 10-3 Ka2 = 6.2 x 10-8 Ka3 = 4.8 x 10-13

The weaker an acid, the stronger its conjugate base:

Acid Ka Conj. Base Kb

HCN 6.2 x 10-10

HC2H3O2 1.8 x 10-5

H2C2O4 5.9 x 10-2

HNO2 5.1 x 10-4

HF 7.2 x 10-4

Soluble Salts effect on pH1) cations and anions found in strong acids or bases have no effect on pH(always spectator ions)

ex: KCl, NaNO3, KNO3, Sr(NO3)2….

Basic Salts: [H+] < [OH-]

1) Salts that produce a basic solution:-salts w/ anions that are conj. Base of weak acids:NaC2H3O2

KNO2

NaCN

2) Basic Anhydrides- Metal oxidesNa2OCs2OSrO

Acidic Salts: [H+] > [OH-]

• 1) ammonium salts:Ex. NH4Cl

2) Acid Anhydrides: Nonmetal oxides oxyacids(NON REDOX!!!)

Ex. CO2

NO2

SO3

3) Transition metal cations-form complex ionsCu(NO3)2

FeCl3

Al(ClO4)3

Is each salt acidic, basic or neutral?KBr NaC2H3O2

NH4Cl CO2

Na2O KNO2

Cu(NO3)2 NH4NO3

N2O KNO3

NaClO4 SrOAl(ClO4)3 NaClKClO2 BaF2

BaCl2 K3PO4

Complete Neutralization Equation:NaVa = NbVb

Neutralization- Acid + Base Salt + H2ONaVa = NbVb

What volume of 0.25M HCl is needed to neutralize 15.0 ml 0.45M Ba(OH)2?

18.5 ml phosphoric acid neutralizes 50.0 ml 1.25 M sodium hydroxide

85.0 ml 0.60M acetic acid neutralizes 75.0 ml KOH. What is the conc. of the base?

Buffer Solutions-solutions that resist great changes in pH when strong acid or base are added.

• All buffers are made by dissolving:1) a weak acid(HA) and an alkali metal salt w/ it’s conjugate base as the anion(NaA) The cation acts only as a spectator.

Or2) A weak base (B) and a chloride salt with BCl as a cation. The anion acts only as a spectator

Fill in the missing part of the buffer:

HA A-

HCNNH3

HNO2

NaClO2

C5H5NNH4

+

KHCO3

Henderson-Hasselbalch eq- pH for buffers:

Henderson-Hasselbalch equation: finds pH of buffered solutions

Find the pH of a 0.150 M HC2H3O2(Ka = 1.8 x 10-5) and 0.350 M NaC2H3O2:

Find the pH of a buffer that is 0.500M HCN (Ka = 4.9 x 10-10) & 1.25M NaCN

652mL of a 1.00M HF & 1.65M NaF solution,(Ka = 7.2 x 10-4)1) Optimum pH

2) pH of the buffer

3) pH after 1.50 grams of KOH are added

pH calculations during a neutralization rxn: titration curve

Titration Curve: graph of pH of sample during titration

Titration Curve: Weak acid titrated with a strong base:

Label: x axis, y axis, equivalence pt, ½ way to equivalence pt.

.125M HC2H3O2 is titrated with .0100M NaOH.• What is the pH before titration begins?

• At equivalence pt?

• ½ way to equivalence pt.?

• 75% to equivalence pt.?

• 95% to equivalence pt.?

Weak polyprotic acid titrated with a strong base:

2.10grams NaOH neutralizes 250. ml of .350M HClO(Ka = 4.0 x 10-8). What is the pH at the equivalence pt.?

How many grams of NaC2H3O2 (Kb = 5.56 x 10-10)are needed to produce 1.25 Liters of a buffer with a pH of 5.36, that is 2.35 M HC2H3O2?

• How many moles of HCl are needed to lower the pH of the previous buffer to 4.00?

• Acids, bases, salts, buffers quiz tomorrow!!!!!

Solubility Equilibria-Rxns are written as solids dissociating into ions, Keq is Ksp(solubility product

constant)• All insoluble salts are never really completely

insoluble. • Very small amount of ionization occurs with all salts.

When the maximum amount of solute dissolves the solution is saturated.

• The maximum concentration that can dissolve is called the molar solubility(x).

Below is a picture of lead(II) Iodide ppt. The Ksp = 8.5 x 10-9. What is the molar solubility?

Solubility Equilibria-Rxns are written as solids dissociating into ions, Keq is Ksp(solubility product

constant)

ZnC2O4 has a molar solubility of 3.5 x 10-5M at 25oC. What is the maximum solubility of the solution?

What is the pH of a saturated Mg(OH)2 solution, Ksp = 5.6 x 10-12M

How many grams Ca3(PO4)2 will dissolve in 750. mL of solution at 25oC, Ksp = 1.0 x 10-26

2.0 grams Nickel(II) carbonate(Ksp = 1.3 x 10-7) are mixed with 2.50 liters of water. Is the solution saturated or unsaturated?

We need to solve for Qsp-rxn quotient for solubility.

If Qsp < Ksp solution is unsaturatedIf Qsp > Ksp solution must be saturatedIf Qsp = Ksp solution is saturated and is about to ppt.