Chapter 14 Acids, Bases, and pH. Comparing of Acids and Bases Observable properties – – Acids are sour – Bases are bitter and slippery to touch *** note.

Chapter 14

Acids, Bases, and pH

Comparing of Acids and Bases

• Observable properties – –Acids are sour–Bases are bitter and slippery to touch

***note – taste and touch

are not safe ways to test chemicals

Comparing of Acids and Bases• Acids and bases turn certain

dyes different colors–acids turn litmus dye red–bases turn litmus dye blue

Many common substances are acids or bases

• common acids –– citric acid, vinegar, – hydrochloric acid, – sulfuric acid

• common bases – – lye/soap, ammonia, – sodium hydroxide, – other metal hydroxides

ReactionsAcids react with metals that

are MORE active than hydrogen

bases do NOT usually react with metals

Reactions• acids also react with ionic

compounds that contain the carbonate ion, CO3

-2

• reaction produces carbon dioxide gas, water, and another compound

Submicroscopic Behavior of Acids

• definition of acid – a substance that produces hydronium ions, H3O+ , when it dissolves in H2O

Ex.

hydronium ions are formed from the transfer of a H+ ion from the acid to H2O

Submicroscopic Behavior of Acids

• acidic hydrogen – any hydrogen atom that can be transferred to H2O.

• to distinguish acidic H’s from other H’s in the compound, acidic H’s are written 1st.

HCl HC2H3O2

HNO3 H2SO4

monoprotic acids contain only one acidic hydrogen

polyprotic acids with two acidic hydrogens are diprotic acids.

polyprotic acids with three acidic hydrogens are triprotic acids

Chemical Reaction Shorthand

• general format for acid dissociation

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

HA (aq) H+ (aq) + A- (aq)

Reaction of acid and H2O to form ions is called acid ionization

Submicroscopic Behavior of Bases

• definition of base – a substance that produces hydroxide ions, OH- when dissolved in water

• 2 kinds– ionic bases– covalent bases

Simple Bases (ionic)

• metal hydroxide = metal ion + OH ion

• the metal hydroxide dissociates in H2O to form a metal ion and a hydroxide ion

***note - H2O does not react here, there is no actual transfer of ions as in the next example and with acids

Bases that Accept H+

• covalent bases react with H2O to form

OH- ions• there is a transfer of H+ from the

water to the base• General equation for bases that accept H+: B + H2O (l) BH+ (aq) + OH- (aq)

NH3 (g) + H2O (l) NH4+ (aq) + OH- (aq)

ammonia + water ammonium hydroxide solution

Other Acids and Bases

• certain compounds act like acids and bases-

• these compounds are: oxides -compounds with oxygen bonded to 1 other element

• they are called anhydrides - contain no water

Other Acids and Bases

acidic anhydrides—nonmetal oxides which react with water to form acids

• CO2 + H2O H2CO3

• SO3 + H2O H2SO

Other Acids and Bases

basic anhydrides—metal oxides which react with water to form acids

• Na2O + H2O 2NaOH

• ZnO + H2O Zn(OH)2

Acid Baseion produced when dissolved in H2O

hydronium ions = H3O+

produce hydroxide ions (OH-) when dissolved in water

properties tart, sour, bitter, slippery,

examples citric acid, vinegar, hydrochloric acid,

lye/soap, ammonia, metal hydroxides

formula usually have H in front of the formula or at the end: HCl, CH3COOH

usually have OH at the end of the formula: KOH, ammonia (NH3) is also a base,

litmus red blue

pH less than 7 greater than 7

Strengths of Acids and Bases• strong acids

completely dissociate into ions– no molecules left

intact

• weak acids partially dissociate (not all come apart) into ions

Strengths of Acids and Bases

• strong bases completely dissociate (come apart) into ions

• weak bases partially dissociate (not all come apart) into ions

strength vs. concentration

• weak and strong refer to dissociation only

• concentrated & dilute = molarity—(M); amount of particles in the solution

The pH Scale

• pH = mathmatical scale; range is 100 to 10-14

= concentration of H3O+ ions

= number from 0 to 14.

acid pH < 7 neutral pH = 7 base pH > 7

• pOH = concentration of OH- ions

pH + pOH = 14

Water is mostly neutral [H+] = [OH-]

Acidic solutions: [H+] > [OH-]

Basic (alkaline) solutions: [OH-] > [H+]

pH of common substances

Example: If [H+] of a solution = 1.0 x 10-11 M

a)Find pH. b)Find pOH. c)Find [OH-]. d)Acid, base, or neutral?

a) [H+] = 1.0 x 10-11 Mb) pH + pOH = 14; 11 + pOH = 14 c) [H+] [OH-] = 10-14M [10-11] [OH-] = 10-

14 Md) pH > 7

pH = 11pOH = 3[OH-] = 10-3 Mbase

Example: If [OH-] of a solution = 1.0 x 10-9 M

a)Find pOH. b)Find pH. c)Find [H+]. d)Acid, base, or neutral?

a) [OH-] = 1.0 x 10-9 Mb) pH + pOH = 14; pH + 9 = 14 c) [H+] [OH-] = 10-14M [H+] [10-9] = 10-14 Md) pH < 7

pOH = 9pH = 5[H+] = 10-5 Macid