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Acids and Bases

Chapter 15

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Overview

Many acids are found in foods. They usually taste sour or tart.Bases are found in many household cleaners and some foods. They often taste bitter.

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Acids

Aqueous solutions of acids taste sour.Often corrosive and/or poisonous

Acids change the color of acid-base indicators in predictable ways.Acids react with bases to produce salts and water.Some acids undergo single-replacement reactions with active metals to release hydrogen gas.Some acids are electrolytes.

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Binary acids

Contain only two different elements

Hydrogen and a more electronegative element

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Naming binary acids

In pure form, they are gases.In aqueous solutions, they are known by their acid names.Always begin with the prefix hydro-Then add the root of the name of the other elementFinally, add the suffix - ic

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Oxyacids

An acid that is a compound of hydrogen, oxygen, and a third element, usually a nonmetal.One type of ternary acids (containing three elements).Usually written as one or more hydrogen atoms followed by a polyatomic anion.Names are based on the anion.

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Sulfuric Acid

The most commonly produced industrial chemical

Over 47 million tons made per year in US

UsesPetroleum refiningFertilizer manufacturingBattery acid

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Sulfuric Acid

Dehydrating agentRemoves water

Causes serious burns by attacking organic compounds in skin

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Nitric Acid

Volatile, unstable liquidBecomes more stable when dissolved in water

Stains proteins yellowCauses serious burnsHas a suffocating odorUsed to make explosives, among other things

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Phosphoric Acid

Used to manufacture fertilizers and animal feedWhen dilute, provides a pleasant, yet sour, taste to beverages.Used as a cleaning agentUsed to make detergents

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Hydrochloric Acid

Produced in your stomachUsed to “pickle” iron and steel

Remove surface impurities

Used for cleaningMuriatic acid – weak HCl

Used in swimming pools and for cleaning

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Acetic Acid

Pungent-smelling liquidCalled glacial acetic acid – freezes at 17 °C.The acid in vinegarUsed to manufacture plasticsUsed in food supplementsUsed as a fungicide

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Discuss

Logic in the laboratoryPage 463

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Bases

Aqueous solutions taste bitterOften caustic

Change the color of indicators in predictable waysDilute aqueous solutions feel slipperyReact with acids to produce salts and waterAre electrolytes

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Arrhenius acids

Increase the concentration of hydrogen ions (H+) in aqueous solutions

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Arrhenius Bases

Increase the concentration of hydroxide, OH- ions , in aqueous solutions.

Could contain hydroxide and dissociateCould react with water to form hydroxide ions

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Aqueous acids

Ionizable hydrogen atomsElectrolytesPolar molecules – hydrogen gets stolen by water to form hydronium ions.

The anion is left alone

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Strong Acids

One that ionizes completely in aqueous solution.

PerchloricHydrochloricNitric

Strong electrolytesDepends on the polarity of the bond with hydrogen and the difficulty of breaking that bond.

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Weak acids

Weak electrolytesSolutions contain hydronium ions, anions, and molecules.SulfuricHydrofluoric

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Organic Acids

Contain the carboxyl group – COOHGenerally weak acids

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Solutions of bases

Most bases are ionic, so they dissociate in solution.When a base dissociates completely, the solution is alkaline.

Li, Na, K, Rb, Cs (alkali metals)

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Molecular bases

Produces a base when it reacts with water.

)()()()( 423 aqOHaqNHlOHaqNH

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Strong bases

Strong electrolytesDepend on the extent to which the base dissociates or adds hydroxide ions to solution.

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Discuss

Section Review on page 462

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Brønsted-Lowry Acids

Molecules or ions that are proton donors

Includes all Arrhenius acids (H+ is a proton)Also includes other substances, like ions

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Examples

HCl + NH3 NH4+ + Cl-

Brønsted-Lowry, but not ArrheniusNo hydrogen or hydronium ions

H2O + NH3 NH4+ + OH-

Water can be a Brønsted-Lowry acid

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Brønsted-Lowry bases

Molecules or ions that are proton acceptors

HCl + NH3 NH4+ + Cl-

Most Arrhenius bases are not Brønsted-Lowry bases

Since they are ionic compounds, they don’t accept protons

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Brønsted-Lowry acid-base reaction

Protons are transferred from the acid to the base

HCl + NH3 NH4+ + Cl-

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Monoprotic acids

Can donate only one proton (hydrogen ion) per molecule

HClO4

HClHNO3

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Polyprotic acids

Can donate more than one proton per molecule

H2SO4

H3PO4

Lose hydrogen atoms one at a timeDiprotic – can donate 2Triprotic – can donate 3

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Lewis acid

An atom, ion, or molecule that accepts an electron pair to form a covalent bondDoes not have to contain hydrogenAny compound in which the central atom has three valence electrons and forms three covalent bonds can be a Lewis acid by forming a fourth covalent bond.

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Lewis base

An atom, ion, or molecule that donates an electron pair to form a covalent bond

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Lewis acid-base reaction

The formation of one or more covalent bonds between an electron-pair donor and an electron-pair acceptor.

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Discuss

Table 15-5 on page 468Section Review, page 468

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Conjugate base

What is left after a Brønsted-Lowry acid gives up a proton.

OHFOHHF 3base conjugate

2acid

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Conjugate acid

What is formed when a Brønsted-Lowry base gains a proton

acid conjugate3

base2

OHFOHHF

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Conjugate acid and base strength

The stronger an acid, the weaker its conjugate base.The stronger a base, the weaker its conjugate acid.

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Reaction direction

Proton-transfer reactions favor the production of the weaker acid and the weaker baseSee table 15-6 on page 471

4324 ClOOHOHHClO

COOCHOHOHCOOHCH 3323

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Amphoteric compounds

Something that can react as either an acid or a baseIf reacting with a stronger acid than itself, acts as a baseIf reacting with a weaker acid, acts as an acid

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Hydroxyl group

Covalently bonded –OH groupThe more polar the O-H bond, the more acidic the compound is.

Hydrogen is attracted away by the water in solution

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Neutralization Reactions

In aqueous solutions, acids and bases react to neutralize each other and form a salt and water.

AntacidsBaking powder

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Neutralization

If we write the net ionic equation, we get H3O+ + OH- 2H2O

Neutralization: the reaction of hydronium and hydroxide ions to make water

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Acid Rain

Many gases produced by industrial processes can dissolve in atmospheric water to produce acids.Leads to acid rain or snow.Acids react with calcium carbonate in marble and erodes it.

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Discuss

Which way do proton-transfer reactions go?How do you know which acid or base is stronger?What is a conjugate acid?What is a conjugate base?Section review #1 on page 475