HA H+
+
Acids, Bases and Salts
A-
Acid-Base Theory Self-Ionization of Water Properties of Acids and Bases The pH Concept Strengths of Acids and Bases Analysis of Acids and Bases Buffers ©1997, West Educational Publishing.
9-1
HA H+
+
Acids and bases
A-
A very important class of chemicals.
• Control CO2 transport in the blood (buffers)
• Amino acids building blocks of protein (contain both and acid and a base)
• Acids are one of the 4 things we can taste (sour)
• Bases feel slippery ©1997, West Educational Publishing.
9-2
HA H+
+
A-
Acidic Citrus fruits Aspirin Coca Cola Vinegar Vitamin C
©1997, West Educational Publishing.
Acids and bases Basic Baking soda Detergents Ammonia cleaners Tums and Rolaids Soap
9-3
HA H+
+
Properties of acids
A-
• Sour taste. • Produce H3O+ when dissolved in water. • Undergo double replacement reactions with solid oxides, hydroxides, carbonates and bicarbonates. 2 HCl + CuO HCl + NaOH 2 HCl + CaCO3 HCl + NaHCO3 ©1997, West Educational Publishing.
CuCl2 + H2O NaCl + H2O CaCl2 + CO2 + H2O NaCl + CO2 + H2O 9 - 10
HA H+
+
Properties of acids
A-
Another property is the ability to react with metals, producing hydrogen gas. Zn + 2 HCl
ZnCl2 + H2
Some metals react better with acids than others. We can show the reactivity using an activity series ©1997, West Educational Publishing.
9 - 11
HA H+
+
A-
Activity series of metals
increasing reactivity
potassium potassium sodium sodium calcium calcium magnesium magnesium aluminum aluminum zinc zinc chromium chromium iron iron nickel nickel tin tin lead lead copper copper silver silver platinum platinum gold ©1997, West Educational Publishing. gold
Reacts violently with cold water Reacts slowly with cold water Reacts very slowly with steam but quite reactive in acid Reacts moderately with high levels of acid
Unreactive in acid 9 - 12
HA H+ + A-
Iron ©1997, West Educational Publishing.
Activity series of metals various metals in HCl
Zinc
Magnesium 9 - 13
HA H+
+
Properties of bases
A-
• Solutions have a slippery or soapy feel. • Will react with acids to produce a salt. Neutralization reaction NaOH + HCl
NaCl + H2O
Neutralization of fatty acids in the skin produce soap. This is why bases feel slippery.
©1997, West Educational Publishing.
9 - 14
HA H+
+
Salts
A-
When acids and bases react, they form water and a salt. KOH + HNO3
KNO3 + H2O (salt)
Salts are typically crystalline, ionic materials. Most ionic compounds can actually be considered salts. ©1997, West Educational Publishing.
9 - 15
HA H+
+
A-
Acid and Base Strength
Strong acids dissociate completely in water HCl, HBr, HI, HClO3, HNO3, HClO4, H2SO4. Weak acids
partially dissociate in water most acids are weak.
Strong bases dissociate completely in water NaOH, LiOH, KOH strong bases are metal hydroxides. Weak bases ©1997, West Educational Publishing.
partially dissociate in water. 9 - 16
HA H+
+
A-
Dissociation
Strong acids and bases • considered to dissociate completely. HCl(aq) + H2O(l)
H3O+ (aq)
+ Cl-(aq)
NaOH(aq) + H2O(l)
Na+(aq) + OH-(aq)
Weak acids and bases • do not dissociate completely. HC2H3O2 (aq) + H2O(l)
H3O+(aq) +C2H3O2-(aq)
NH3 (aq) + H2O(l)
NH4+
©1997, West Educational Publishing.
+ OH (aq) (aq) 9 - 17
HA H+
+
A-
Acid dissociation constant, Ka
The strength of a weak acid can be expressed as an equilibrium. HA (aq) + H2O(l)
H3O+(aq) + A- (aq)
The strength of a weak acid is related to its equilibrium constant, Ka. Ka = [A-][H3O+] [HA] ©1997, West Educational Publishing.
We We omit omit water. water. It’s It’s already already included included in in the the constant. constant. 9 - 18
HA
Dissociation of bases, Kb
H+ + A-
The strength of a weak base can also be expressed as an equilibrium. B (aq) + H2O(l)
BH+(aq) +OH- (aq)
The strength of a weak base is related to its equilibrium constant, Kb. Kb = [OH-][BH+] [B] ©1997, West Educational Publishing.
9 - 19
HA H+
+
A-
Ka and Kb values
For weak acids and bases Ka and Kb
always have values that are smaller than one.
• Acids with a larger Ka are stronger than ones with a smaller Ka.
• Bases witha larger Kb are stronger than ones with a smaller Kb.
Most acids and bases are considered weak. ©1997, West Educational Publishing.
9 - 20
HA H+
+
A-
pH and pOH
We need to measure and use acids and bases over a very large concentration range. pH and pOH are systems to keep track of these very large ranges. pH = -log[H3O+] pOH = -log[OH-] pH + pOH = 14 ©1997, West Educational Publishing.
9 - 21
Logarithms As with exponents, this is a way of working with very large and very small numbers logn
• the abbreviation for the term logarithm • n is the base
log10 common logs • based on 10 • the only type we will be using • the 10 is usually omitted We will only be using base 10 logs ©1997, West Educational Publishing.
9 - 22
Logarithms For ‘whole’ numbers, the common log and the exponent in scientific notation are the same. log(1000) = 3
1000 = 103
logs of other numbers are no integers but the idea is the same. log(1500) = 3.176
©1997, West Educational Publishing.
1500 = 103.176
9 - 23
Logarithms A positive log represents a number greater than one. log(13456) = 4.1289 A negative log represents a number smaller than one. log(0.00291) = -2.54 You CAN’T take the log of a negative value. log( -235 ) ©1997, West Educational Publishing.
= error 9 - 24
value 1000 500 100 50 10 5 1 0.5 0.1 0.05 0.01 0.005 0.001
log(value) Logarithms 3.0 The sign tells us if the 2.7 number is larger or 2.0 smaller than one. 1.7 1.0 The number before the 0.7 decimal point tells us 0.0 where the decimal -0.3 point would be in -1.0 scientific notation. -1.3 -2.0 The number after the -2.3 decimal point tells us -3.0 what the number is.
©1997, West Educational Publishing.
9 - 25
Log practice Determine the following with your calculator: log(12345) 4.1
