Ch 18 Acids and Bases

Acid-sour taste, burning feeling on open wounds, changes blue litmus paper red, neutralizes a base
•reacts with active metals to form H2 gas

base- bitter taste, slippery feeling, changes red litmus paper blue, neutralizes an acid
•active metals react with water to form H2 gas and metallic hydroxide
electrolytes (ions)-conduct a current when dissolved into water.
•acids, bases, and salts
HCl(aq) ---> H+(aq) + Cl-(aq)

NaOH(aq) ---> Na+(aq) + OH-(aq)

NaCl(aq) ---> Na+(aq) + Cl-(aq)

Arrhenius definition:

-Arrhenius Acids form hydronium ions, H3O+

-Arrhenius Bases form hydroxide ions, OH-

both in aqueous solutions.

Arrhenius Acid:

HCl ---> H+ + Cl-H+ = hydrogen ion

H+ + H2O ---> H3O+H3O+ = hydronium ion

HCl(g) + H2O(l) ----> H3O+(aq) + Cl-(aq)

Arrhenius Base:

NaOH(s) ----> Na+(aq) + OH-(aq)

Bronsted definition:

Bronsted Acid-donates an H+ ion (proton)

Bronsted Base-accepts an H+ ion (proton)

CH3COOH + H2O ---> H3O+ + CH3COO-

HCl + NH3 ---> NH4+ + Cl-

HSO4- + OH- ---> H2O + SO42-

Conjugate Acid-Base Pairs:

acid + base ---> conjugate acid + conjugate base

HCl + H2O  H3O+ + Cl-

NH3 + H2O NH4+ + OH-

CH3COOH + H2O H3O+ + CH3COO-

strong acids have weak conjugate base pair

weak acids have strong conjugate base pair

Water As An Acid & A Base:

HCl + H2O ---> H3O+ + Cl-

NH3 + H2O ---> NH4+ + OH-

Amphiprotic (amphoteric)- can act both as an acid & base

Strength vs. Concentration

Concentrated and Dilute

Strong and Weak

Acids and Bases may be very concentrated (3M or 5M) but not necessarily strong.

Ex: pouring 3M acetic acid (vinegar) or 0.1M HCl over a wound.

Strong Acids: HCl, HBr, HI, HNO3, H2SO4, HClO4

Strong Bases: all hydroxides of Group 1A2A except Be

Strong Acids & Bases react to completion

dissociate (ionize) completely in water (become all products), single arrow,Large Ka

Weak Acids & Bases react incompletely & reach equilibrium

dissociate (ionize) slightly in water (reactants & products present), double arrow,Small Ka

Acid Dissociation Constant, Ka

HA(aq) + H2O(l)  H3O+(aq) + A-(aq)

Keq =Ka =

HF(aq) + H2O(l) <==> H3O+(aq) + F-(aq)Ka =

Problem: A chemists mixes 0.1000 mole of aspirin in 1.00 L of water to produce a weak monoprotic acid, acetylsalicylic acid. When the solution reaches equilibrium, she measures the concentration of H3O+ to be 0.0057 M. Calculate the Ka for aspirin.

Problem: Formic acid is a weak monoprotic acid that is partly responsible for the irritation of insect bites. If the initial concentration of formic acid is 0.100M and the equilibrium concentration of H3O+ is 0.0042 M, calculate the Ka for formic acid.

Chapter 19

The Self Ionization of Water, Kw

H2O + H2O  H3O+ + OH-

Keq =Ion product constant of water:Kw =

pH scale: a measure of the amount of hydronium ion concentration or the level of acidity and alkalinity of a substance.

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0714

  • pH + pOH = 14
  • pH = -log[H3O+](pH is the negative log of [H3O+])
  • pOH = -log[OH-]
  • [H3O+][OH-] = 1 x 10-14

1. If the concentration of H3O+ in blood is 4.0x10-8M, is the blood acidic, basic, or neutral? What is the concentration of the OH- ions? What is the pOH?

2. What is the concentration of OH- ions in chocolate milk if [H3O+] = 4.5 x 10-7M? Is chocolate milk acidic, basic or neutral?

3. What is the concentration of H3O+ ions in black coffee if [OH-] = 1.3 x 10-9M. Is black coffee acidic, basic, or neutral?

4. Normal rainwater has a pH near 6. In rainwater that falls close to a coal-burning power plant, the concentration of H3O+ ions is 6.23x10-4M. What is the pH? Is this more or less acidic than normal rainwater?

5. In household bleach, the concentration of OH- ions is 5.0 x 10-2M. What is the pH?

Indicators: identify acids & bases (pH ranges) by color change

-phenolphthalein pink in base, clear in acid

-bromthymol blueblue in base, yellow in acid

HIn(aq) + H2O(l)  H3O+(aq) + In-(aq)“In-” represents the base form of the indicator

“HIn” represents the acid form of the indicator

Adding acid, which adds H3O+ions to the solution (b/c H+ reacts with H2O to produce H3O+), shifts the equilibrium to the left, increasing [HIn] and thus changing to that indicator’s color in that pH range.

Adding base, which removes H3O+ (b/c OH- reacts with H3O+to produce H2O), shifts the equilibrium to the right, increasing [In-] and thus changing to that indicator’s color in that pH range.

Buffers: solutions that resist changes in pH even when acids or bases are added.

Buffer Capacity - the amount of H+ or OH- that a buffer system can “absorb” without a significant change in pH

buffer system- a solution that absorbs or releases H+ ions without a large change in pH.

NH3 + H2O <==> NH4+ + OH-
NH4+ + H2O <==> NH3 + H3O+
OH- + H3O+ ---> 2H2O

-look for a -weak acid & strong conjugate baseCH3COOHCH3COO-

-weak base & strong conjugate acidNH3NH4+

-the salt of a conjugate pairNaCH3COO

-most organisms have buffers within their circulatory system- blood

Bicarbonate buffer system (carbonic acid and bicarbonate buffer)

Carbonic anhydrase

H2O+ CO2 <======> H2CO3Carbonic acid

H2CO3 +H2OH3O+ + HCO3-Bicarbonate ion

H3O+ + HCO3-H2CO3 + H2Oaddition of acid

Bicarbonate ion (hydrogen carbonate)

HCO3-+ OH- H2O + CO32-addition of base

Neutralization Reactions:

strong acid + strong base ---> salt + water

HCl(aq) + NaOH(aq) ---> NaCl(aq) + H2O(l)

(there must be no H+ in the salt)

Acid disposal: neutralize w/ base b/f disposingAcid spill: neutralize with baking soda (sodium bicarbonate)

test pH w/ litmus paperuntil no gas more gas is liberated

Titration: an analytical method in which a standard solution (known concentration) is used to determine the concentration of an acid or base by adding base to acid & finding the equivalence pt. (pt. of neutralization)

equivalence point- having equal numbers of acid (H3O+) and base(OH-) ions in solution, point of complete neutralization.

Polyprotic Acids- has more than one ionizable hydrogen atom.

H2SO4 +H2O  H3O+ + HSO4-large Ka-strong acid

HSO4- + H2O  H3O+ + SO4-2small Ka -weak acid

e.g. 2 mol HCl and 1 mol Mg(OH)2

1 mole of HCl neutralizes 1 mole of NaOH

recall: M=moles/volume

Molarity x Volume = moles

M1V1=M2V2

1. 42.5 mL of 1.03M NaOH neutralizes 50.0mL of CH3COOH. What is the acid’s concentration?

2. Solutions of sodium hydroxide are used to unclog drains. A 43.0 mL volume of NaOH was titrated with 32.0 mL of 0.100M HCl. What is the molarity of the sodium hydroxide solution?

3. A volume of 25.mL of 0.120M H2SO4 neutralizes 40.mL of an NaOH solution. What is the concentration of the NaOH solution?

Titration curves for strong acid v strong base.

Adding acid into the base

Adding base into the acid

Titration curves for strong acid v weak base

Adding acid into the base

Adding base into the acid

Titration curves for weak acid v strong base

Adding acid into the base

Adding base into the acid