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

Chapter Outline 15.1 Acids and Bases 15.8 Ionization of Water 15.2 Reactions of Acids 15.9 Introduction to pH 15.3 Reactions of Bases 15.10 Neutralization 15.4 Salts 15.11 Writing Net Ionic Equations 15.5 Electrolytes and Nonelectrolytes 15.12 Acid Rain 15.6 Dissociation and Ionization of Electrolytes 15.13 Colloids 15.7 Strong and Weak Electrolytes 15.14 Properties of Colloids

15.1 Acids and Bases

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.

Base Properties bitter or caustic taste a slippery, soapy feeling. the ability to change litmus red to blue the ability to interact with acids

Svante Arrhenius was a Swedish scientist who lived from 1859-1927. In 1884 he advanced a theory of acids and bases.

An Arrhenius acid “is a hydrogen-containing substance that dissociates to produce hydrogen ions.” HA → H+ + A- acid

An Arrhenius base is a hydroxide-containing substance that dissociates to produce hydroxide ions in aqueous solution. MOH → M+(aq) + OH-(aq) base

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

J. N. Bronsted (1897-1947) was a Danish chemist and T. M 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.

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

HCl + H2O(l) → H3O+(aq) + Cl-(aq) Bronsted-Lowry Acid proton acceptor Bronsted-Lowry Base proton donor HCl + H2O(l) → H3O+(aq) + Cl-(aq)

hydrogen ion does not exist in water a hydronium ion is formed hydrogen ion combines with water

Conjugate acid-base pairs differ by a proton. When an acid donates a proton it becomes the conjugate base. HCl(g) → Cl-(aq) acid base

Conjugate acid-base pairs differ by a proton. When a base accepts a proton it becomes the conjugate acid. H2O (l) → H3O+(aq) base acid

Conjugate acid-base pairs differ by a proton. HCl(g) + → Cl-(aq) H3O+(aq) H2O (l) acid base

Conjugate acid-base pairs differ by a proton. HCl(g) + → Cl-(aq) H3O+(aq) H2O (l) acid base

In 1923 G. N. Lewis developed a more comprehensive theory of acids and bases. The Lewis theory deals with the way in which a substance with an unshared pair of electrons reacts in an acid-base type of reaction.

A Lewis acid is an electron-pair acceptor. A Lewis base is an electron-pair donor.

Electron Pair Acceptor Lewis Acid Electron Pair Acceptor Electron pair donated to H+ Lewis Base Electron Pair Donor

Electron Pair Acceptor Lewis Acid Electron Pair Acceptor Electron pair donated to B Lewis Base Electron Pair Donor

15.2 Reactions of Acids

In aqueous solution, the H+ or H3O+ ions are responsible for the characteristic reactions of acids.

acid + metal → hydrogen + ionic compound Reaction with Metals Acids react with metals that lie above hydrogen in the activity series of elements to produce hydrogen and an ionic compound (salt): acid + metal → hydrogen + ionic compound 2HCl(aq) + Ca(s) → H2(g) + CaCl2(aq) H2SO4(aq) + Mg(s) → H2(g) + MgSO4(aq)

3Zn(s) + 8HNO3(dilute) → 3Zn(NO3)2 (aq) + 2NO(g) + 4H2O(l) Reaction with Metals Oxidizing acids react with metals to produce water instead of hydrogen: 3Zn(s) + 8HNO3(dilute) → 3Zn(NO3)2 (aq) + 2NO(g) + 4H2O(l)

Reaction with Bases The reaction of an acid with a base is called a neutralization reaction. In an aqueous solution the products are a salt and water: HBr(aq) + KOH(aq) → KBr(aq) + H2O(l) acid base salt 2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l) acid base salt

Reaction with Metal Oxides In an aqueous solution the products are a salt and water. This type of reaction is closely related to that of an acid with a base: 2HCl(aq) + Na2O(s) → 2NaCl(aq) + H2O(l) acid metal oxide salt H2SO4(aq) + MgO(s) → MgSO4(aq) + H2O(l) acid salt metal oxide

Reaction with Carbonates Most acids react with carbonates to produce carbon dioxide, water and an ionic compound: 2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + H2O(l) + CO2(g) acid carbonate salt H2SO4(aq) + MgCO3(s) → MgSO4(aq) + H2O(l) + CO2(g) acid carbonate salt HCl(aq) + NaHCO3(aq) → NaCl(aq) + H2O(l) + CO2(g) acid carbonate salt

Carbonic acid (H2CO3) is not the product when an acid reacts with a carbonate because carbonate spontaneously decomposes into carbon dioxide and water. H2CO3(aq) → CO2(g) + H2O(l)

15.3 Reactions of Bases

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: HBr(aq) + KOH(aq) → KBr(aq) + H2O(l) acid base salt 2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l) acid base salt

Amphoteric Hydroxides Hydroxides of certain metals are amphoteric, meaning they are capable of reacting as either an acid or a base: Zn(OH)2 + 2HCl(aq) → ZnCl2(aq) + 2H2O(l) base acid salt Zn(OH)2 + 2KOH(aq) → K2Zn(OH)4(aq) Lewis acid base

Reaction of NaOH and KOH with Certain Metals Some amphoteric metals react directly with the strong bases sodium hydroxide and potassium hydroxide to produce hydrogen: base + metal + water → salt + hydrogen 2KOH(aq) + 2Al(s) + 6H2O(l) → 2KAl(OH)4(aq) + 3H2(g) Lewis acid 2NaOH(aq) + Zn(s) + 2H2O(l) → Na2Zn(OH)4(aq) + H2(g) Lewis acid

15.4 Salts

Salts can be considered compounds derived from acids and bases 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). Salts are usually crystalline and have high melting and boiling points. Chemists use the terms ionic compound and salt interchangeably.

Salt Formation NaOH HCl NaCl The negative ion of the salt is derived from the acid. The positive ion of the salt is derived from the base. NaOH HCl base acid NaCl salt

15.5 Electrolytes and Nonelectrolytes

Nonelectrolytes are substances whose aqueous solutions do not conduct electricity. Electrolytes are substances whose aqueous solutions conduct electricity. Nonelectrolytes are not capable of producing ions in solution. Electrolytes are capable of producing ions in solution.

Classes of compounds that are electrolytes are: acids bases salts solutions of oxides that form an acid or a base

15.6 Dissociation and Ionization of Electrolytes

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

In a crystal of sodium chloride positive sodium ions are bonded to negative chloride ions. 15.2

In aqueous solution the sodium and chloride ions dissociate from each other. 15.2

In aqueous solution the sodium and chloride ions dissociate from each other. 15.2

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

The equation representing the dissociation of NaCl is: NaCl(s) + (x+y)H2O → Na+(H2O)x + Cl-(H2O)y The equation can be written more simply as: NaCl(s) → Na+(aq) + Cl-(aq)

Ionization is the formation of ions. Ionization occurs as the result of a chemical reaction of certain substances with water. Ionization is the formation of ions.

Acetic acid ionizes in water to form acetate ion and hydronium ion. HC2H3O2 + H2O H3O+ + C2H3O2- → Lewis acid Lewis base The equation can be written more simply as: HC3H3O2 H+ + C2H3O2- → In the absence of water, ionization reactions do not occur.

15.7 Strong and Weak Electrolytes

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

Most salts are strong electrolytes Strong acids and bases (highly ionized) are strong electrolytes. Weak acids and bases (slightly ionized) are weak electrolytes.

1% ionized 100% ionized Strong Acid Weak Acid HCl Solution HC2H3O2 Solution 15.3

HC2H3O2(aq) → H+ (aq) + C2H3O2(aq) Both the ionized and unionized forms of a weak electrolyte are present in aqueous solution. HC2H3O2(aq) → H+ (aq) + C2H3O2(aq) → ionized unionized

HNO3, a strong acid, is 100 % dissociated. HNO3(aq) → H+(aq) + NO3(aq) HNO2, a weak acid, is only slightly ionized. HNO2(aq) → H+(aq) + NO2(aq) →

NaOH → Na+(aq) + OH-(aq) Electrolytes yield two or more ions per formula unit upon dissociation. NaOH → Na+(aq) + OH-(aq) two ions in solution per formula unit Na2SO4 → 2Na+(aq) + SO4-(aq) three ions in solution per formula unit Fe2(SO4 )3 → 2Fe3+(aq) + 3SO4-(aq) five ions in solution per formula unit

NaOH → Na+(aq) + OH-(aq) Electrolytes yield two or more moles of ions per mole of electrolyte upon dissociation. NaOH → Na+(aq) + OH-(aq) 1 mole Na2SO4 → 2Na+(aq) + SO4-(aq) 1 mole 2 moles Fe2(SO4 )3 → 2Fe3+(aq) + 3SO4-(aq) 1 mole 2 moles 3 moles

Colligative Properties of Electrolyte Solutions

NaOH → Na+(aq) + OH-(aq) Substances that form ions in aqueous solutions change the colligative properties of water in proportion to the number of ions formed. NaOH → Na+(aq) + OH-(aq) 1 mole Two moles of ions will depress the freezing point of water twice that of one mole of a nonelectrolyte. Fe2(SO4 )3 → 2Fe3+(aq) + 3SO4-(aq) 1 mole 2 moles 3 moles Five moles of ions will depress the freezing point of water five times that of one mole of a nonelectrolyte.

15.8 Ionization of Water

→ H2O + H2O → H3O+ + OH- → H2O → H+ + OH- Water ionizes slightly. hydroxide ion hydronium ion acid base H2O + H2O → H3O+ + OH- → Water ionization can be expressed more simply as: H2O → H+ + OH- → [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.

15.9 Introduction to pH

pH is the negative logarithm of the hydrogen ion concentration. pH = -log[H+]

Calculation of pH

pH = -log[H+] [H+] = 1 x 10-5 when this number is exactly 1 pH = this number without the minus sign. when this number is exactly 1 pH = 5

one significant figure pH = -log[H+] [H+] = 2 x 10-5 when this number is between 1 and 10 one significant figure ph = 4.7 pH is between this number and the next lower number (between 4 and 5). one decimal place The number of decimal places of a logarithm is equal to the number of significant figures in the original number.

What is the pH of a solution with an [H+] of 1.0 x 10-11? 2 significant figures pH = - log(1.0 x 10-11) pH = 11.00 2 decimal places

log[H+] = log (6.0 x 10-4) = -3.22 pH = - log[H+] = -(3.22) = 3.22 What is the pH of a solution with an [H+] of 6.0 x 10-4? 2 significant figures log[H+] = log (6.0 x 10-4) = -3.22 pH = - log[H+] = -(3.22) = 3.22 2 decimal places

log[H+] = log(5.47 x 10-8) = -7.262 pH = - log[H+] = -(7.262) = 7.262 What is the pH of a solution with an [H+] of 5.47 x 10-8? 3 significant figures log[H+] = log(5.47 x 10-8) = -7.262 pH = - log[H+] = -(7.262) = 7.262 3 decimal places

The pH scale of Acidity and Basicity 15.4

15.10 Neutralization

HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) 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

Titrations

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

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) 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? Convert mL of NaOH to liters of NaOH The equation for the reaction is HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) acid base salt Calculate the liters of NaOH that react. The unit of volume when using molarity is liters. Calculate the moles of NaOH that react.

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) 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 moles of NaOH that react equals the moles of HCl that react. The mole ratio of HCl to NaOH is 1:1 0.00630 mol NaOH react. 0.00630 mol HCl react. The molarity of the HCl solution is

15.11 Writing Net Ionic Equations

HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) In the formula equation all compounds are written using their molecular or formula expressions. HCl(aq) + KOH(aq) → KCl(aq) + H2O(l) acid base salt In the total ionic equation all ions present in solution are written. (H+ + Cl-) + (K+ + OH-) → K+ + Cl- + H2O In the net ionic equation only the ions that react are written. Ions that do not participate in a chemical reaction are called spectator ions. Cl- ion does not react. K+ ion does not react. H+(aq) + OH-(aq) → H2O(l)

Rules for Writing Equations Strong electrolytes in solution are written in their ionic form. Weak electrolytes are written in their molecular form. Nonelectrolytes are written in their molecular form.

Insoluble substances, precipitates and gases are written in their molecular forms. The net ionic equation should include only substances that have undergone a chemical change. Spectator ions are omitted from the net ionic equation. Equations must be balanced both in atoms and in electrical charge.

Examples

formula equation total ionic equation net ionic equation 2AgNO3(aq) + BaCl2(aq) → 2AgCl(s) + Ba(NO3)2(aq) formula equation spectator ions (2Ag+ + ) + (Ba2+ + 2Cl-) → 2AgCl(s) + (Ba2+ + ) total ionic equation precipitate Ag+ + Cl- → AgCl(s) net ionic equation

formula equation total ionic equation net ionic equation spectator ions total ionic equation gas net ionic equation

formula equation total ionic equation net ionic equation Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) formula equation spectator ion Mg(s) + (2H+ + 2Cl-) → (Mg2+ + 2Cl-)+ H2(g) total ionic equation Electrical charge on both sides of the equation = +2 Mg + 2H+ → Mg2+ + H2(g) net ionic equation

15.12 Acid Rain

The increase in acidity might be from natural or industrial sources. Acid rain is any atmospheric precipitation that is more acidic than usual. The increase in acidity might be from natural or industrial sources.

CO2(g) + H2O(l) H2CO3(aq) H+ + HCO3 The pH of rain is lower in the eastern US and higher in the western US. Unpolluted rain has a pH of 5.6 because of carbonic acid formation in the atmosphere. CO2(g) + H2O(l) H2CO3(aq) H+ + HCO3 →

Process of Acid Rain Formation emission of nitrogen and sulfur oxides into the air transportation of these oxides into the atmosphere chemical reactions between the oxides and water forming sulfuric acid (H2SO4) and nitric acid (HNO3) rain or snow, which carries the acids to the ground From the burning of fossil fuels.

Effects of Acid Rain freshwater plants and animals decline significantly when rain is acidic aluminum is leached from the soil into lakes and adversely affects fish gills. the waxy protective coat on plants is dissolved making them vulnerable to bacteria and fungal attack

Effects of Acid Rain it is responsible for extensive and continuing damage to buildings, monuments and statues it reduces the durability of paint and promotes the deterioration of paper, leather and cloth

15.13 Colloids

Colloid A dispersion in which the dispersed particles are larger than the solute ions or molecules of a true solution and smaller than the particles of a mechanical suspension.

Colloid is derived from the Greek word “kolla” meaning “glue.” The term colloid does not imply a system has a gluelike quality.

The fundamental difference between a colloidal dispersion and a true solution is the size of the particles. In ordinary solutions the size of solute particles range from 0.1 to 1 nm. The size of colloidal particles range from 1 to 1,000 nm. In a solution the particles are usually single ions or molecules. In a colloid the particles are usually aggregations of ions or molecules.

15.14 Properties of Colloids

In 1827 Robert Brown illuminated an aqueous suspension of pollen under a high powered microscope. He observed a trembling erratic motion of the pollen grains. This erratic motion is characteristic of colloids in general. This random motion is called Brownian movement.

The Tyndall effect occurs because colloidal particles are large enough to scatter light. When an intense beam of light is passed through an ordinary solution and viewed at an angle, the beam passing through the solution is hardly visible. A beam of light is clearly visible and sharply outlined when it is passed through a colloidal dispersion. This phenomenon is known as the Tyndall effect.

Colloidal particles have huge surface areas in comparison to the volume of the same particles if they were aggregated into one large particle. Colloidal particles become electrically charged when they adsorb ions on their surfaces. This occurs because surface atoms or ions of the colloid attract and adsorb ions or polar molecules from the dispersion medium.

The End