Acids & Acids & BasesBases

Chemistry 6.0

Naming Acids Review: A. Binary – H +one anion Prefix “hydro”+ anion name +“ic”acid

Ex) HCl hydrochloric acid

Ex) H3P hydrophosphoric acid

B. Tertiary – H + polyatomic anion no Prefix “hydro”

(oxo) end “ate” = “ic” acidend “ite” = “ous” acid

Ex) H2SO4 sulfuric acid

Ex) H2SO3 sulfurous acid

Properties of Acids and Bases:

Taste TouchReactions

with MetalsElectrical

Conductivity

Acid sour

looks like water, burns, stings

Yes-produces

H2 gas

electrolyte in solution

Base

(alkali)bitter

looks like water, feels

slippery

No Reaction

electrolyte in solution

IndicatorsIndicators: Turn 1 : Turn 1 colorcolor in an acid in an acid and another color in a and another color in a basebase..

A.A. Litmus PaperLitmus Paper: Blue and Red: Blue and RedAn aciAn aciDD turns blue litmus paper turns blue litmus paper reDreDA A BBase turns red litmus paper ase turns red litmus paper BlueBlue..

B.B. PhenolphthaleinPhenolphthalein: : colorless in an acid colorless in an acid and pink in a baseand pink in a base

C.C. pH paperpH paper: : range of colors from range of colors from acidic to basicacidic to basic

D.D. pH meterpH meter: : measures the measures the concentration of Hconcentration of H++ in solution in solution

NeutralizationNeutralization: A reaction between an : A reaction between an acidacid and and basebase. When an acid and base . When an acid and base neutralize, neutralize, waterwater and a and a salt salt (ionic solid)(ionic solid) form. form.

AcidAcid + + BaseBase → → SaltSalt + + WaterWater

Ex) Ex) HCl + NaOHHCl + NaOH → → NaClNaCl + + HOHHOH

ReactionsReactions

ReactionsReactions

Acids and MetalsAcids and Metals– HA + M HA + M H H22 + MA + MA

A = anionA = anion

M = metalM = metal

– 2HCl + Mg 2HCl + Mg H H22 + MgCl + MgCl22

Acids and CarbonatesAcids and Carbonates– HA + MCOHA + MCO33 MA + CO MA + CO22 + H + H22OO

– HCl + LiHCl + Li22COCO33 2LiCl + CO 2LiCl + CO22 + H + H22OO

Arrhenius Definition (1884):A. An acid dissociates in water to produce more

hydrogen ions, H+.HCl H+1 + Cl-1

B. A base dissociates in water to produce more hydroxide ions, OH-.

NaOH Na+1 + OH-1

C. Problems with Definition:• Restricts acids and bases to water solutions.• Oversimplifies what happens when acids

dissolve in water.• Does not include certain compounds that have

characteristic properties of acids & bases. Ex) NH3 (ammonia) doesn’t fit

Bronsted-Lowry Definition (1923):A. An acid is a substance that can donate hydrogen ions.

Ex) HCl → H+ + Cl-

– Hydrogen ion is the equivalent of a proton.– Acids are often called proton donors.– Monoprotic (HCl), diprotic (H2SO4) , triprotic (H3PO4)

B. A base is a substance that can accept hydrogen ions. Ex) NH3 + H+ → NH4

+

– Bases are often called proton acceptors.C. Advantages of Bronsted-Lowry Definition

•Acids and bases are defined independently of how they behave in water.

•Focuses solely on hydrogen ions.

Hydronium Ion:

Hydronium Ion – H3O+ This is a complex ion that forms in water.

H+1 + H2O H3O+1

To more accurately portray the Bronsted-Lowry, the hydronium ion is used instead of the hydrogen ion.

STRONG Acid/Base versus WEAK Acid/Base

Strength refers to the % of molecules that form IONS.

A strong acid or base will completely ionize (>95% as ions). This is represented by a single () arrow.

HNO3 + H2O H3O+ + NO3-

A weak acid or base will partially ionize (<5% as ions). This is represented by a double (↔) arrow.

HOCl + H2O ↔ H3O+ + ClO-

HF < HCl < HBr < HIincreasing strength

7 Strong AcidsHNO3 H2SO4 HClO3

HClO4 HCl HBrHI

8 Strong BasesLiOH NaOH KOHRbOH CsOH Ca(OH)2

Sr(OH)2 Ba(OH)2

Strength vs. Concentration

• Strength refers to the percent of molecules that form ions

• Concentration refers to the amount of solute dissolved in a solvent. Usually expressed in molarity.

• See “Acids: Concentration vs. Strength”

Conjugate Acid-Base Pairs: A pair of compounds that differ by only one hydrogen ion

A. Acid donates a proton to become a conjugate base.

B. Base accepts proton to become a conjugate acid.

• A strong acid will have a weak conjugate base.

• A strong base will have a weak conjugate acid.

Acid (A), Base (B), Conjugate Acid (CA), Conjugate Base (CB)

NH3 + H2O ↔ NH4+ + OH-

HCl + H2O ↔ Cl- + H3O+

• Base and Conjugate Acid are a Conjugate Pair.

• Acid and Conjugate Base are a Conjugate Pair.

B

B

A

A

CA CB

CB CA

1. H2O + H2O ↔ H3O+ + OH− B A CA

CB

2. H2SO4 + OH− ↔ HSO4− + H2O

A B CB CA

3. HSO4− + H2O ↔ SO4

−2 + H3O+ A B CB CA

4. OH− + H3O+ ↔ H2O + H2O B A CA CB

AciDonates & Bases accept

Ionization of Acids & Bases

• H2SO4 2 H+ + SO4-2

– Sulfuric acid

• H3PO3 – Phosphorous acid

• Ca(OH)2 – Calcium hydroxide

3 H+ + PO3-3

Ca+2 + 2 OH-1

The Self-ionization of Water & pH1. Water is amphoteric, it acts as both an acid and a base in the

same reaction.

Ex) H2O(l) + H2O(l) ↔ H3O+(aq) + OH-

(aq)

Keq = equilibrium constant = [H3O+] [OH-]Because reactants and products are at equilibrium, liquid water is

not included in the equilibrium expression

@ 25C, [H3O+] = 1 x 10-7 M and [OH-] = 1 x 10-7 M Kw = ion product constant or equilibrium constant for water

Kw = [H3O+] [OH-] = 1 x 10-14 M2

1.0 x 10-14 M2 = [1.0 x 10-7 M] [1.0x10-7 M]

1.0 x 10-14 = [H3O+] [OH-]

Acids: [H3O+] > 1 x 10-7 MBases: [OH-] > 1 x 10-7 M

Using Kw in calculations: If the concentration of H3O+ in the blood is 4.0 x 10-8 M, what is the concentration of OH ions in the blood? Is blood acidic, basic or neutral?

Kw = [H3O+] [OH-]1.0 x 10-14 M2 = [4.0 x 10-8 M] [OH-]

2.5 x 10-7 M = [OH-] slightly basic

The pH scale (1909): the power of Hydrogen

A. Measure of H3O+ in solution.

B. pH = -log[H3O+]

C. Range of pH: 0-14

pH < 7: acid

pH > 7: base

pH = 7: neutralD. pOH = -log[OH-]

E. pH + pOH = 14

D. pH = -log [H3O+]

E. [H3O+] [OH-] = 1.0 x 10-14

F. pH + pOH = 14

H+

OH-

pH1 7 14

H+

OH

-

pH [H3O+] [OH-]

14 1x10-14 1x100

13 1x10-13 1x10-1

12 1x10-12 1x10-2

11 1x10-11 1x10-3

10 1x10-10 1x10-4

9 1x10-9 1x10-5

8 1x10-8 1x10-6

7 1x10-7 1x10-7

6 1x10-6 1x10-8

5 1x10-5 1x10-9

4 1x10-4 1x10-10

3 1x10-3 1x10-11

2 1x10-2 1x10-12

1 1x10-1 1x10-131

14

Significant Digits RuleSignificant Digits Rule

The number of digits The number of digits AFTER AFTER THE DECIMAL POINTTHE DECIMAL POINT in your in your answer should be equal to the answer should be equal to the number of significant digits in number of significant digits in your your original numberoriginal number

Ex -log[8.7x10Ex -log[8.7x10-4-4MM] ] Calc Answer = 3.Calc Answer = 3.060604807474 04807474 Sig Fig pH = 3.Sig Fig pH = 3.0606

Acid-Base Titration1. An acid-base titration is a carefully controlled

neutralization reaction or redox which can determine concentration of an unknown solution.

2. To determine the concentration of an unknown substance, a standard solution is needed. This solution has a known concentration.

3. Titration curve: graph that

shows how pH changes

during a titration.

4. An indicator, usually phenolphthalein, is used in a titration.

• Colorless in an acid, pink in a base.

5. The point at which enough standard solution is added to neutralize the unknown solution is called the equivalence point.

6. The point at which the indicator changes color is called the endpoint.

7. Therefore: [H+] = [OH-] at the equivalence point

Ex) A volume of 50.0 mL of 0.150M sodium hydroxide neutralizes 30.0mL of a sulfuric acid solution. What is the concentration of the sulfuric acid solution?

H2SO4 + NaOH Na2SO4 + HOHNote: Mole ratio between acid an base in not 1:1

2 2

Mb = 0.125M