Chapter 8

Acids and Bases

산과 염기

Acids• What is an Acid?

– Hydrogen ion, proton (H+) donor

• Properties– Taste sour, reacts with metals, donates protons

• Classes of Acids

• Common Acids

Acid Reaction• 물과의 반응

HA H+ + A-

H+ + H2O H3O+

HA(aq) + H2O(l) H3O+(aq) + A-

(aq)

• Acids increase the hydronium ion concentration in water

Hydronium Ion

Types of Acids• Strong

– Acids that dissociate completely in water– Inorganic Acids– HCl, H2SO4, HNO3, HClO4

• Weak– Acids that partially dissociate in water– Organic Acids– 강산을 제외한 대부분의 산

Bases• What is a base?

– Hydrogen ion acceptor

– Hydroxide ion (OH-) and Ammonia (NH3)

• Properties– Taste bitter, forms insoluble hydroxide with

metals, accepts hydrogen ions

• Common Bases

Base Reaction• Generic Reaction in Water

BOH B+ + OH-

OH- + H2O H2O + OH-

BOH(aq) B+(aq)

+ OH-(aq)

• Bases increase the hydroxide ion concentration

Chemical Equilibrium• What determines strong vs weak?

• 화학 평형 Chemical Equilibrium– The state in a reaction when there in no change

in the concentration of the reactants or products– Reactions that proceed in both directions at the

same time (rate)

Carbon Dioxide• Carbon Dioxide, CO2

CO2 + H2O H2CO3

H2CO3 + H2O H3O+ + HCO3-

HCO3- + H2O H3O+ + CO3

-2

H2CO3- + 2 H2O 2 H3O+ + CO3-2

Acid-Base Pairs• Acid that loses a H+ becomes a base

– Called conjugate base

H2CO3 + H2O H3O+ + HCO3-

• 짝산 - 짝염기

Water• Auto protolysis

H2O + H2O H3O+ + OH-

• Amphiprotic (Amphoteric)– substance that can behave as an acid or a base

Water

• [H+] = 1 x 10-7 mol/L

• [OH-] = 1 x 10-7 mol/L

Kw = [H+] x [OH-] = 1 x 10-14

-

322OH OH OH OH

pH Scale• Concentration [H+] or [OH-]

pH = - log [H+]

pOH = - log [OH+]

• What is the pH of neutral water?

pH + pOH = 14

Conversions

• acidic/neutral /basic

• pH of common substances

OH H

pOH pH

-

Measuring pH• Meters

– meter uses a standard electrode to measure the hydrogen ion concentration, [H+]

• Indicators– Molecules that change color depending on the

hydrogen ion concentration, [H+]

• Common Indicators

Natural Indicators• Anthocyanins

– found in flower, fruits and vegetables

+O

OH

OH

OH

H O+O

OH

OH

OH

H O

OH

+O

OH

OH

OH

H O

OH

OH

Neutralization

• 중화– process of adding acid or base to a solution to

achieve a neutral solution, pH = 7– equal amounts of acid and base

• 적정 , Titration– determination of the concentration of a

solution by reaction with a solution of known concentration

Neutralization• 당량점 Equivalence Point

– the point in a titration when equal portions of the reactants have been added (stoichiometry)

• Mole Acid = Moles of Base

MAVA = MBVB

Buffers• 완충용액 , Buffers

– chemical systems composed of acid-base pairs that resist changes in pH

– buffers contain an acid-base pair which maintain the pH

• Example – Acetic Acid and Sodium Acetate

H3C C

O

O- Na+H3C C

O

OH

Buffers

• pH = pKa + log{[base form]/[acid form]}

Homework• 교과서 281 쪽 연습문제

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