Acids and BasesChapter 19

DHS Chemistry

DefinitionsBronsted – Lowry

Arrhenius

Bronsted-Lowry Acid

•Proton (hydrogen ion) donor.•Proton = H+

HCl + H20 Cl- + H30+ donor acceptor

Acid

Bronsted-Lowry Base

•Proton (hydrogen ion) acceptor.•Proton = H+

HCl + +NH3 NH4+ + Cl-

donor acceptor

Base

Arrhenius Acid

Produces H+/H3O+ ions

Ex. HCl + H20 H30+ + Cl-

acid

Arrhenius Base

Produces H+/H3O+ ion

Ex. NH3 + H2O NH4+ + OH-

Base

Properties

Acid Properties•Typically acids start with ________ in their formulas.

Like... HCl and H2SO4

hydrogen

Acid Properties•____ taste•turn blue litmus paper red (pink)

Sour

Acid Properties•react with bases to produce salt and water (neutralization)

•electrolytes (may be strong or weak)

© Prentice Hall

Properties - Acids

Acid Properties

•contain hydrogen and most react with active metals to produce hydrogen gas

Base Properties•Most bases (not all) have OH in their chemical formulas.

Like... NaOH and KOH

Base Properties

•Bitter taste

Antacids help neutralizes

stomach acid. They are bases.

Base Properties

•Feel slippery

•turn red litmus paper blue

•react with an acid to produce salt and water (neutralization)

•electrolytes (may be strong or weak)

Properties - Bases

Litmus Paper

Aci ase Re lueBD

Common Ones

A. Common AcidsAcid Formul

aMajor Uses

sulfuric acid

H2SO4Car batteries,

production of metals

phosphoric acid H3PO4 Found in soft drinks

Nitric acid HNO3 Production of explosives

hydrochloric acid HCl Cleaning of metals

Most commonly produced in the

world

Common Bases

Base Formula

Major Uses

ammonia NH3Refrigerant,

household cleaners

sodium hydroxide

NaOH Drain cleaner

potassium hydroxide

KOH To increase pH of acidic soils

Strength/Electrolytic Behavior of Acids and

Bases

Strong Acids• Ionize almost completely

(almost 100%)• Strong electrolytes

(when dissolved) • Strong electrolyte = bright light

bulb

Examples of Strong Acids

•HCl, HBr, HI, HNO3, H2SO4

These acids ionize almost completely in water.

*memorize those that are highlighted

Weak Acids• Ionize partially•Weak electrolytes

(when dissolved) •Weak electrolyte = dim light

bulb

Examples of Weak Acids

•HF, HCN, HC2H3O2, H2CO3

These acids ionize almost completely in water.

*memorize those that are highlighted

Strong Bases• Ionize almost completely

(almost 100%)• Strong electrolytes

(when dissolved) • Strong electrolyte = bright light

bulb

Strong Bases

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

These bases ionize almost completely in water.

*memorize those that are highlighted

Weak Bases• Ionize partially•Weak electrolytes

(when dissolved) •Weak electrolyte = dim light

bulb

Weak bases

•CH3N2, NH3, NaCN, Mg(OH)2

These bases ionize almost completely in water.

*memorize those that are highlighted

•Some substances can act as both an acid and a base – these substances are considered amphoteric.

EX: HCl + H20 H30+ + Cl- water as a base

acid base

NH3 + H20 NH4+ + OH- water as

an acid

base acid

H20 + H20 H30+ + OH- water as an

acid

pure water has H2O, H3O+, OH- & base

Polyprotic acids• Acids that can contain multiple

hydrogens to donate.

• Match the terms with the probable acid

monoprotic H2SO4

diprotic H3PO4

polyprotic HCl

•Acids that contain 1 ionizable hydrogen are monoprotic acids.Ex. HCl, HBr

Polyprotic acids

•Acids that contain 2 ionizable hydrogens are diprotic acids.Ex. H2SO4

Polyprotic acids

•Acids that contain 3 ionizable hydrogens are triprotic/polyprotic acids.Ex. H3PO4

Polyprotic acids

II. Acid and Base Reactions

A. Reactions Involving Acids

1. Acids with Active Metals– Acids will react with active metals

(metals more reactive than hydrogen) to release hydrogen gas

– General Form: H + HX MX + H2

EX:Mg(s) + 2HNO3(aq) Mg(NO3)2(aq) + H2(g)Active metal acid salt/ionic compound hydrogen gas

2. Nonmetallic Oxide and Water•acids can be produced

from the reaction of a nonmetallic oxide (ex. SO3) and water

•General Form: NMO + water HX

EX: SO3(g) + H2O(l) H2SO4(aq)

acid anhydride water acid

•(a substance that produces an acid when combined with water is called an acid anhydride.)

3. Acids with Carbonates

•acids will react with carbonates (ex. NaCO3) to produce a salt and water and carbon dioxide gas

EX: Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + CO2(g)+

H20(l)carbonate acid waterCarbon dioxide

Salt/ionic compound

B. Reactions Involving Bases

1. Metallic Oxide and Water•a metallic oxide (ex. Na2O)

and water will combine to produce a base

•General Form: MO + H2O Base

metal oxide

1. Metallic Oxide and Water•General Form: MO + H2O Base

metal oxide

EX: Na2O(s) + H2O(l) 2NaOH(aq)

• (a substance that produces a base when combined with water is called a basic anhydride.)

Metal oxide water base(basic anhydride)

C. Neutralization Reactions

•The reaction of an acid with a base produces water and a class of compounds called salts.

HA + BOH B A + H2O

ex. HCl(aq) + NaOH(aq) NaCl (aq) +

H2O(l)

acid base salt water

Ex. The salt is highlighted in each case.

HCl + NaOH → NaCl + H2O HC2H3O2 + KOH KC2H3O2 + H2O

H2SO4 + 2 NH4OH (NH4) 2SO4 + H2O

HC2H3O2 + NH4OH NH4C2H3O2 + H2O

Strong acid plus strong base

Weak acid plus strong base

Strong acid plus weak base

Weak acid plus weak base

•Salts are compounds consisting of an anion from an acid and a cation from a base.

•If you mix a solution of a strong acid with a strong base, a neutral solution results.

•Reactions in which an acid and a base react in aqueous solution are called neutralization reactions.

•All neutralization reactions are double-replacement reactions

Practice1. ID the type, complete, and

balance these reactions involving acids and bases.

a) hydrochloric acid + Al

b) sulfuric acid + zinc

6HCl(aq) + 2Al(s) 2AlCl3(aq) + 3H2(g)

H2SO4(aq) + Zn(s) ZnSO4(aq) + H2 (g)

Acid + active metal

Acid + active metal

Practice1. ID the type, complete, and

balance these reactions involving acids and bases.

c) nitric acid + potassium hydroxide

d) calcium oxide + water

Acid + base (neutralization)

Metal oxide + water

HNO3(aq) + KOH(aq) KNO3(aq) + H2O(l)

CaO(s) + H2O(l) Ca(OH)2(aq)

III. Strength of Acids and Bases

A. Ionization•acids will form ions (electrolytes) when dissolved in water in a process called ionization.

EX:HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)

Bases

•Bases also will form ions (electrolytes) when dissolved in a process called dissociation.

EX: NaOH(s) Na+(aq) + OH-(aq)H2O

•One way to measure the strength of an acid or a base is to measure how much of the original molecule remains after it has been added to water. If little remains, the acid or base is strong. If a lot of the original molecule remains, the acid or base is weak.

•For example, when HCl is added to water, nearly all of the HCl molecules are converted to ions.

HCl + H2O H3O+ +Cl-

Strong Acid

•When acetic acid is added to water, most of the acetic acid molecules remain as molecules and only a small portion of the molecules are converted to ions.

Weak Acid

6 H-A

H+

A-

H+

H+

H+

H+

H+

A-

A-

A-

A-A-

STRONG ACI D100 % I ONI ZED I N WATER

6 H-A

A-H+

H-A

H-A

H+

A-

H-A

H-A

WEAK ACI DLI TTLE I ONI ZATI ON I N WATER

A-

H+

water

acid

proton

anion

H-A

6 H-A

H+

A-

H+

H+

H+

H+

H+

A-

A-

A-

A-A-

6 H-A

H+

A-

H+

H+

H+

H+

H+

A-

A-

A-

A-A-

STRONG ACI D100 % I ONI ZED I N WATER

6 H-A

A-H+

H-A

H-A

H+

A-

H-A

H-A

WEAK ACI DLI TTLE I ONI ZATI ON I N WATER

A-

H+

water

acid

proton

anion

H-A

A-

H+

water

acid

proton

anion

H-A

• Do not confuse the terms strong and weak with the terms concentrated and dilute. Strength refers to what % of the original molecules convert to ions in water. Concentrated or dilute refer to how many total moles there are in water.

Strong acids (lots of H+ ions): HCl, HBr, HI, HNO3, H2SO4Highlight the acids that will ionize almost completely in water.

Weak acids (some H+ ions): HF, HCN, HC2H3O2, H2CO3

Strong bases (lots of OH- ions): NaOH, KOH, Ca(OH)2, LiOH, CsOH, RbOH, Sr(OH)2

Highlight the bases that are very soluble in water.

Weak bases (some OH- ions): CH3N2, NH3, NaCN, Mg(OH)2

B. pH Scale

Hydronium vs Hydroxide

•Hydronium H3O+

– A hydrogen ion in water

– H+ + H2O H3O+

– H+ and H3O+ used interchangeably

– For acids

•Hydroxide OH-

– For bases

1. Background•Any aqueous solution contains both hydronium ions and hydroxide ions. This stems from the fact that water will ionize to a very small amount:

Note: for pure water, the number of hydronium ions is

equal to the number of hydroxide ions.

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

•when an acid is added to water, the number of hydronium ions increases

HCl(aq) + H2O(l) H3O+(aq) + Cl-

(aq)

•when a base is added to water, the number of hydroxide ions increases

H2O(l)

NaOH(s) Na+(aq) + OH-

(aq)

•it is the ratio of hydronium ions to hydroxide ions that determines whether a solution will be an acid, a base, or neutral

•acid: contains more hydronium ions than hydroxide ions

•base: contains more hydroxide ions than hydronium ions

•neutral: the # of hydronium ions is equal to the # of hydroxide ions

2. pH Scale•a measure of the number of hydronium or hydroxide ions is the pH scale

•it is based on the concentration of hydrogen and hydroxide ions in solution

•pH is defined as the negative logarithm of the hydrogen ion concentration

[ ] = concentration (molarity)

•notice pH is based on a log (base 10) scale

pH = -log([H+])

pH= -log([H3O+])

pH Scale

•the typical pH scale runs from 0 to 14 .

•a pH of 7 is considered neutral which means that the concentration of hydrogen ions and the concentration of hydroxide ions are equal

•as you go down on the pH scale (< 7), solutions are considered acidic

•solutions with pH’s greater than 7 are considered basic

Summary of the pH scale

pH Category Concentration of ions

< 3 strong acid

many H3O+

3-7 Weak acid H3O+ > OH-

7 neutral H3O+ = OH-

7-11 Weak base H3O+ < OH-

> 11 strong base

many OH-

Practice1. Determine whether the following are

a strong acid, a weak acid, a strong base, a weak base, neutral solution

a. pH = 2.5b. lots of hydroxide ions, hardly any hydronium ions

c. little more hydroxide ions than hydronium ions

Strong acid

strong Base

Weak base

•There is also something called pOH, which is a measure of the concentration of hydroxide ions.

pOH = -log ([OH-]

•pH and pOH are related by the following:

14 = pH + pOH

•Again, for strong, single hydroxide bases, [OH-] = molarity of the base.

Ex: What is the pOH of KOH if the pH is 14?

pH + pOH = 1414 + pOH = 14

pOH = 0

Practice1. Determine whether the following

are a strong acid, a weak acid, a strong base, a weak base, neutral solution

pOH = 2.5

12.0 M NaOH

pH = 11.5strong base

pOH = 1.07pH = 12.9strong base

IV. Titrations

A. Titrations

•The concentration of an acid (or base) in solution can be determined by performing a neutralization reaction.

acid + base salt + water

•An indicator is used to show when neutralization has occurred.

•An indicator is a substance that forms different colors in different pH solutions. Phenolphthalein is a common indicator used in acid-base titrations. It will change from colorless in acidic environments to pink in basic environments.

Acid Base Indicators(pH sensitive)

Litmus paper

Acid Base Indicators(pH sensitive)

pH paper

Acid Base Indicators(pH sensitive)

Universal Indicator

Acid Base Indicators(pH sensitive)

Phenolphthalein

Acid Base Indicators(pH sensitive)

Red Cabbage Juice

• The solution of known concentration is called the standard solution. The standard solution is added using a buret.

• The process of adding a known amount of solution of known concentration to determine the concentration of another solution is called titration.

• The point at which the indicator changes color is the end point of the titration.

50

40

30

20

10

0

Titrant- standarized base in burette

Titrand-unknown acid containing indicator and a means f or stirring

Informal titration

•This can also be done less “formally” using any volume measures. The results won’t be as accurate, but it gets you close.

•Example: (drops, substitute for mL)

Steps in a formal titration1. A measured volume

of a solution of unknown concentration (acid or base) is added to an Erlenmeyer flask.

2. A solution of known molarity (acid or base) is added to a buret.

Known MV measured

Known VUnknown M

3. Several drops of an indicator are added to the unknown solution

4. Measured volumes of a solution of known molarity (acid or base) are mixed into unknown solution until the indicator just barely changes color to pink.

Known MV measured

Known VUnknown M

The end point

Phenolphthalein indicator

Clear = Acid Pink = Base

How to read a buret

•This can also be done less “formally” using any volume measures. The results won’t be as accurate, but it gets you close.

Example: (drops, substitute for mL)

B. Solving Titration Problems

Remember, in order for the solution to be neutral,

V = volumeM = molarity (M)A = acidB = base

If the ratio of H+ to OH- is 1:1, then

MAVA = MBVB

(similar to dilutions)

1) It takes 26.23 mL of a 1.008 M NaOH solution to neutralize 35.28 mL of a monoprotic acid solution. What is its molarity?

MA = ? M MB = 1.008 M

VA = 35.28 mL VB = 26.23 mL

MAVA = MBVB

MA(35.28 mL) = (1.008 M) (26.23 mL)

MB = 0.749 M

1.008 M Base

35.28 mL of ?? M acid

Keep adding base until there

is a color change.

Volume of base added = 26.23 mL

2) If 15.50 mL of Ca(OH)2 solution were neutralized with 23.40 mL of 0.533 M H2SO4, what is the concentration of the Ca(OH)2 ?

MA = 0.533 M MB = ? M

VA = 23.40 mL VB = 15.50 mL

MAVA = MBVB

(0.533 M)(23.40 mL) = MB (15.50 mL)

0.805 M = MB

Ex 3: 25.00 mL of 0.720 M nitric acid (HNO3) is used to completely neutralize a 1.0 M NaOH solution. What volume of NaOH is present?

MA = 0.720 M MB = 1.0M

VA = 25mL VB = ??

MAVA = MBVB

(0.720 M)(25 mL) = (1.0 M) VB

18.00 mL = VB

Practice Box Answers

1) 0.385 M H3PO4

2) 5.76 x 10-3 M NaOH3) 0.840 M NaOH4) 55.6 mL H2CO3

1. What is the molarity of phosphoric acid if 15.0 mL of the solution is completely neutralized by 38.5 mL of 0.150 M Al(OH)3?

H3PO4 Al(OH)3

MA = ?? MB = 0.150MVA = 15mL VB = 38.5mL

MAVA = MBVB

MA(15mL) = (0.150M)(38.5mL)

MA = 0.385M H3PO4

2. It takes 26.23 mL of a 0.01 M NaOH solution to neutralize a 45.56 mL of a HCl solution. What is the concentration of the acid?

HCl NaOH

MA = ? MB = 0.01M

VA = 45.56 mL VB = 26.23 mL

MAVA = MBVB

MA(45.56 mL) = (0.01 M)(26.23 mL)

MA = 5.76 x 10-3 M HCl

3. What is the molarity of potassium hydroxide if 20.0 mL of the solution is neutralized by 28.0 mL of 0.60 M HCl?

HCl NaOHMA = 0.60M MB = ??

VA = 28.0mL VB = 20.0mL

MAVA = MBVB

(0.60M)(28.0mL) = MB(20.0mL)0.840M NaOH = MB

4. How many mL of 0.45 M HCl must be added to 25.0 mL of 1.00 M KOH to make a neutral solution?

HCl KOH

MA = 0.45 M MB = 1.00 M

VA = ?? VB = 25.0 mL

MAVA = MBVB

MA(0.45 mL) = (1.00 M)(25.0 mL)

MA = 55.6 mL HCl