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Acids, Bases and Salts Chapter 15

Acids, Bases and Salts Chapter 15

Hein and Arena Eugene Passer Chemistry Department Bronx Community College© John Wiley and Sons, Inc

Version 2.0

12th Edition

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Chapter Outline15.1 Acids and Bases

15.2 Reactions of Acids

15.3 Reactions of Bases15.10 Neutralization

15.11 Writing Net Ionic Equations

15.4 Salts

15.5 Electrolytes and Nonelectrolytes

15.9 Introduction to pH

15.12 Acid Rain

15.13 Colloids

15.6 Dissociation and Ionization of Electrolytes

15.7 Strong and Weak Electrolytes

15.8 Ionization of Water

15.14 Properties of Colloids

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15.115.1

Acids and BasesAcids and Bases

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Acid Properties• sour taste

• change the color of litmus from blue to red

• react with – metals such as zinc and magnesium to

produce hydrogen gas

– hydroxide bases to produce water and an ionic compound (salt)

– carbonates to produce carbon dioxide.

These properties are due to the release of hydrogen ions, H+, into water solution.

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Base Properties• bitter or caustic taste

• a slippery, soapy feeling.

• the ability to change litmus red to blue

• the ability to interact with acids

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• Svante Arrhenius was a Swedish scientist who lived from 1859-1927.

• In 1884 he advanced a theory of acids and bases.

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An Arrhenius acid “is a hydrogen-containing substance that dissociates to produce hydrogen ions.”

HA → H+ + A-

acid

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An Arrhenius base is a hydroxide-containing substance that dissociates to produce hydroxide ions in aqueous solution.

MOH → M+(aq) + OH-(aq)base

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An Arrhenius acid solution contains an excess of H+ ions.

An Arrhenius base solution contains an excess of OH- ions.

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• J.N. Bronsted (1897-1947) was a Danish chemist and T. M. Lowry (1847-1936) was an English chemist.

• In 1923 they advanced their theory of acids and bases.

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A Bronsted-Lowry acid is a proton (H+) donor.

A Bronsted-Lowry base is a proton (H+) acceptor.

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HCl + H2O(l) → H3O+(aq) + Cl-(aq)

proton acceptorBronsted-Lowry Baseproton donorBronsted-Lowry Acid

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hydrogen ion does not exist

in water

hydrogen ion combines with water

a hydronium ion is formed

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HCl(g) → Cl-(aq)baseacid

Conjugate acid-base pairs differ by a proton.

When an acid donates a proton it becomes the conjugate base.

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Conjugate acid-base pairs differ by a proton.

When a base accepts a proton it becomes the conjugate acid.

H3O+(aq)H2O (l) →acidbase

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Conjugate acid-base pairs differ by a proton.

baseacid

HCl(g) + → Cl-(aq) + H3O+(aq)H2O (l)

acidbase

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Conjugate acid-base pairs differ by a proton.

baseacid

HCl(g) + → Cl-(aq) + H3O+(aq)H2O (l)

acidbase

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A Lewis acid is an electron-pair acceptor.

A Lewis base is an electron-pair donor.

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15.315.3

Reactions of BasesReactions of Bases

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HBr(aq) + KOH(aq) → KBr(aq) + H2O(l)

Reaction with Acids The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water:

2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l)

acid base salt

acid base salt

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15.415.4

SaltsSalts

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Salts can be considered compounds derived from acids and bases. They consist of positive metal or ammonium ions combined with nonmetal ions (OH- and O2- excluded).

Chemists use the terms ionic compound and salt interchangeably.Salts are usually crystalline and have high melting and boiling points.

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NaOH HCl

NaCl

base acid

salt

The positive ion of the salt is derived from the base.

The negative ion of the salt is derived from the acid.

Salt Formation

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15.515.5

Electrolytes and Electrolytes and NonelectrolytesNonelectrolytes

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Electrolytes are substances whose aqueous solutions conduct electricity.

Nonelectrolytes are substances whose aqueous solutions do not conduct electricity.

Electrolytes are capable of producing ions in solution.

Nonelectrolytes are not capable of producing ions in solution.

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Classes of compounds that are

electrolytes are:– acids

– bases

– salts

– solutions of oxides that form an acid or a base

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15.615.6

Dissociation andDissociation andIonization of ElectrolytesIonization of Electrolytes

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Dissociation is the process by which the ions of a salt separate as the salt dissolves.

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In a crystal of sodium chloride positive sodium ions are bonded to negative chloride ions.

15.2

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In aqueous solution the sodium and chloride ions dissociate from each other.

15.2

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In aqueous solution the sodium and chloride ions dissociate from each other.

15.2

34Na+ and Cl- ions hydrate with H2O molecules.15.2

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Acetic acid ionizes in water to form acetate ion and hydronium ion.

HC2H3O2 + H2O H3O+ + C2H3O2-→→

Lewis acid Lewis base Lewis acid Lewis base

HC3H3O2 H+ + C2H3O2-→→

The equation can be written more simply as:

In the absence of water, ionization reactions do not occur.

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15.715.7

Strong and Strong and Weak ElectrolytesWeak Electrolytes

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Strong Electrolyte An electrolyte that is essentially 100% ionized in aqueous solution.Weak Electrolyte An electrolyte that is ionized to a small extent in aqueous solution.

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• Most salts are strong electrolytes

• Strong acids and bases (highly ionized) are strong electrolytes.

• Weak acids and bases (slightly ionized) are weak electrolytes.

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HCl Solution

HC2H3O2 Solution

Strong Acid Weak Acid1% ionized100%

ionized

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HC2H3O2(aq) → H+ (aq) + C2H3O2(aq) -2 3 2C H O ( )aq→→

Both the ionized and unionized forms of a weak electrolyte are present in aqueous solution.

ionizedunionized

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HNO3(aq) → H+(aq) + NO3(aq)-3NO ( )aq

HNO3, a strong acid, is 100 % dissociated.

HNO2(aq) → H+(aq) + NO2(aq)-2NO ( )aq→→

HNO2, a weak acid, is only slightly ionized.

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Electrolytes yield two or more ions per formula unit upon dissociation.

NaOH → Na+(aq) + OH-(aq)

Na2SO4 → 2Na+(aq) + SO4-(aq) 2-

4SO ( )aq

two ions in solution per formula unit

Fe2(SO4 )3 → 2Fe3+(aq) + 3SO4-(aq) 2-43SO ( )aq

three ions in solution per formula unit

five ions in solution per formula unit

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Electrolytes yield two or more moles of ions per mole of electrolyte upon dissociation.

NaOH → Na+(aq) + OH-(aq)

1 mole 1 mole 1 mole

Na2SO4 → 2Na+(aq) + SO4-(aq) 2-

4SO ( )aq1 mole 2 moles 1 mole

Fe2(SO4 )3 → 2Fe3+(aq) + 3SO4-(aq) 2-43SO ( )aq

1 mole 2 moles 3 moles

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Colligative Properties ofElectrolyte Solutions

Colligative Properties ofElectrolyte Solutions

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15.815.8

Ionization of WaterIonization of Water

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Water ionizes slightly.

acid base acid baseH2O + H2O → H3O+ + OH- →→

hydronium ion

hydroxide ion

H2O → H+ + OH- →→Water ionization can be expressed more simply as:

[H3O+] or [H+] = 1.0 x 10-7 mol/L

[OH-] = 1.0 x 10-7 mol/L

Two out of every 1 billion water molecules are ionized.

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15.915.9

Introduction to pHIntroduction to pH

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pH is the negative logarithm of the hydrogen ion concentration.

pH = -log[H+]

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Calculation of pHCalculation of pH

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pH = -log[H+]

[H+] = 1 x 10-5

when this number is exactly 1

pH = this number without the minus sign.

pH = 5

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pH = -log[H+]

[H+] = 2 x 10-5

when this number is between 1 and 10

The number of decimal places of a logarithm is equal to the number of significant figures in the original number.

pH is between this number and the next lower number (between 4 and 5).

one significant figure

ph = 4.7

one decimal place

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What is the pH of a solution with an [H+] of 1.0 x 10-11?

pH = - log(1.0 x 10-11)

pH = 11.00

2 decimal places

2 significant figures

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What is the pH of a solution with an [H+] of 6.0 x 10-4?

pH = - log[H+] = -(3.22) = 3.22

2 decimal places

2 significant figures

log[H+] = log (6.0 x 10-4) = -3.22

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What is the pH of a solution with an [H+] of 5.47 x 10-8?

pH = - log[H+] = -(7.262) = 7.262

3 decimal places

3 significant figures

log[H+] = log(5.47 x 10-8) = -7.262

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The pH scale of Acidity and Basicity

15.4

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15.1015.10

NeutralizationNeutralization

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Neutralization The reaction of an acid and a base to form a salt and water.

HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) acid base salt

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TitrationsTitrations

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Titration The process of measuring the volume of one reagent required to react with a measured mass or volume of another reagent.

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42.00 mL of 0.150 M NaOH solution is required to neutralize 50.00 mL of hydrochloric acid solution. What is the molarity of the acid solution?

The equation for the reaction is

molMolarity =

L

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) acid base salt

Convert mL of NaOH to liters of NaOH

The unit of volume when using molarity is liters.

Calculate the moles of NaOH that react.

0.150 mol NaOH0.004200 L = 0.00630 mol NaOH

1L

1 L42.00 mL = 0.04200 L

1000 mL

Calculate the liters of NaOH that react.

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42.00 mL of 0.150 M NaOH solution is required to neutralize 50.00 mL of hydrochloric acid solution. What is the molarity of the acid solution.

The equation for the reaction is

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) acid base salt

The mole ratio of HCl to NaOH is 1:1The moles of NaOH that react equals the moles of HCl that react.

0.00630 mol NaOH react. 0.00630 mol HCl react.

molM = =

L0.0630 mol HCl

0.05000 L

0.126 M HCl

The molarity of the HCl solution is

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15.1215.12

Acid RainAcid Rain

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Acid rain is any atmospheric precipitation that is more acidic than usual.

The increase in acidity might be from natural or industrial sources.

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• The pH of rain is lower in the eastern US and higher in the western US.

CO2(g) + H2O(l) H2CO3(aq) H+ + HCO3→→ →→

• Unpolluted rain has a pH of 5.6 because of carbonic acid formation in the atmosphere.

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2. transportation of these oxides into the atmosphere

3. chemical reactions between the oxides and water forming sulfuric acid (H2SO4) and nitric acid (HNO3)

4. rain or snow, which carries the acids to the ground

Process of Acid Rain Formation

1. emission of nitrogen and sulfur oxides into the air

From the burning of fossil fuels.

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2. aluminum is leached from the soil into lakes and adversely affects fish gills.

3. the waxy protective coat on plants is dissolved making them vulnerable to bacteria and fungal attack

Effects of Acid Rain

1. freshwater plants and animals decline significantly when rain is acidic

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5. it reduces the durability of paint and promotes the deterioration of paper, leather and cloth

Effects of Acid Rain

4. it is responsible for extensive and continuing damage to buildings, monuments and statues