acids and bases chapter 19 dhs chemistry. definitions bronsted – lowry arrhenius
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Acids and BasesChapter 19
DHS Chemistry
DefinitionsBronsted – Lowry
Arrhenius
Bronsted-Lowry Acid
•Proton (hydrogen ion) donor.•Proton = H+
HCl + H20 Cl- + H30+ donor acceptor
Acid
Bronsted-Lowry Base
•Proton (hydrogen ion) acceptor.•Proton = H+
HCl + +NH3 NH4+ + Cl-
donor acceptor
Base
Arrhenius Acid
Produces H+/H3O+ ions
Ex. HCl + H20 H30+ + Cl-
acid
Arrhenius Base
Produces H+/H3O+ ion
Ex. NH3 + H2O NH4+ + OH-
Base
Properties
Acid Properties•Typically acids start with ________ in their formulas.
Like... HCl and H2SO4
hydrogen
Acid Properties•____ taste•turn blue litmus paper red (pink)
Sour
Acid Properties•react with bases to produce salt and water (neutralization)
•electrolytes (may be strong or weak)
© Prentice Hall
Properties - Acids
Acid Properties
•contain hydrogen and most react with active metals to produce hydrogen gas
Base Properties•Most bases (not all) have OH in their chemical formulas.
Like... NaOH and KOH
Base Properties
•Bitter taste
Antacids help neutralizes
stomach acid. They are bases.
Base Properties
•Feel slippery
•turn red litmus paper blue
•react with an acid to produce salt and water (neutralization)
•electrolytes (may be strong or weak)
Properties - Bases
Litmus Paper
Aci ase Re lueBD
Common Ones
A. Common AcidsAcid Formul
aMajor Uses
sulfuric acid
H2SO4Car batteries,
production of metals
phosphoric acid H3PO4 Found in soft drinks
Nitric acid HNO3 Production of explosives
hydrochloric acid HCl Cleaning of metals
Most commonly produced in the
world
Common Bases
Base Formula
Major Uses
ammonia NH3Refrigerant,
household cleaners
sodium hydroxide
NaOH Drain cleaner
potassium hydroxide
KOH To increase pH of acidic soils
Strength/Electrolytic Behavior of Acids and
Bases
Strong Acids• Ionize almost completely
(almost 100%)• Strong electrolytes
(when dissolved) • Strong electrolyte = bright light
bulb
Examples of Strong Acids
•HCl, HBr, HI, HNO3, H2SO4
These acids ionize almost completely in water.
*memorize those that are highlighted
Weak Acids• Ionize partially•Weak electrolytes
(when dissolved) •Weak electrolyte = dim light
bulb
Examples of Weak Acids
•HF, HCN, HC2H3O2, H2CO3
These acids ionize almost completely in water.
*memorize those that are highlighted
Strong Bases• Ionize almost completely
(almost 100%)• Strong electrolytes
(when dissolved) • Strong electrolyte = bright light
bulb
Strong Bases
•NaOH, KOH, Ca(OH)2, LiOH, CsOH, RbOH, Sr(OH)2
These bases ionize almost completely in water.
*memorize those that are highlighted
Weak Bases• Ionize partially•Weak electrolytes
(when dissolved) •Weak electrolyte = dim light
bulb
Weak bases
•CH3N2, NH3, NaCN, Mg(OH)2
These bases ionize almost completely in water.
*memorize those that are highlighted
•Some substances can act as both an acid and a base – these substances are considered amphoteric.
EX: HCl + H20 H30+ + Cl- water as a base
acid base
NH3 + H20 NH4+ + OH- water as
an acid
base acid
H20 + H20 H30+ + OH- water as an
acid
pure water has H2O, H3O+, OH- & base
Polyprotic acids• Acids that can contain multiple
hydrogens to donate.
• Match the terms with the probable acid
monoprotic H2SO4
diprotic H3PO4
polyprotic HCl
•Acids that contain 1 ionizable hydrogen are monoprotic acids.Ex. HCl, HBr
Polyprotic acids
•Acids that contain 2 ionizable hydrogens are diprotic acids.Ex. H2SO4
Polyprotic acids
•Acids that contain 3 ionizable hydrogens are triprotic/polyprotic acids.Ex. H3PO4
Polyprotic acids
II. Acid and Base Reactions
A. Reactions Involving Acids
1. Acids with Active Metals– Acids will react with active metals
(metals more reactive than hydrogen) to release hydrogen gas
– General Form: H + HX MX + H2
EX:Mg(s) + 2HNO3(aq) Mg(NO3)2(aq) + H2(g)Active metal acid salt/ionic compound hydrogen gas
2. Nonmetallic Oxide and Water•acids can be produced
from the reaction of a nonmetallic oxide (ex. SO3) and water
•General Form: NMO + water HX
EX: SO3(g) + H2O(l) H2SO4(aq)
acid anhydride water acid
•(a substance that produces an acid when combined with water is called an acid anhydride.)
3. Acids with Carbonates
•acids will react with carbonates (ex. NaCO3) to produce a salt and water and carbon dioxide gas
EX: Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + CO2(g)+
H20(l)carbonate acid waterCarbon dioxide
Salt/ionic compound
B. Reactions Involving Bases
1. Metallic Oxide and Water•a metallic oxide (ex. Na2O)
and water will combine to produce a base
•General Form: MO + H2O Base
metal oxide
1. Metallic Oxide and Water•General Form: MO + H2O Base
metal oxide
EX: Na2O(s) + H2O(l) 2NaOH(aq)
• (a substance that produces a base when combined with water is called a basic anhydride.)
Metal oxide water base(basic anhydride)
C. Neutralization Reactions
•The reaction of an acid with a base produces water and a class of compounds called salts.
HA + BOH B A + H2O
ex. HCl(aq) + NaOH(aq) NaCl (aq) +
H2O(l)
acid base salt water
Ex. The salt is highlighted in each case.
HCl + NaOH → NaCl + H2O HC2H3O2 + KOH KC2H3O2 + H2O
H2SO4 + 2 NH4OH (NH4) 2SO4 + H2O
HC2H3O2 + NH4OH NH4C2H3O2 + H2O
Strong acid plus strong base
Weak acid plus strong base
Strong acid plus weak base
Weak acid plus weak base
•Salts are compounds consisting of an anion from an acid and a cation from a base.
•If you mix a solution of a strong acid with a strong base, a neutral solution results.
•Reactions in which an acid and a base react in aqueous solution are called neutralization reactions.
•All neutralization reactions are double-replacement reactions
Practice1. ID the type, complete, and
balance these reactions involving acids and bases.
a) hydrochloric acid + Al
b) sulfuric acid + zinc
6HCl(aq) + 2Al(s) 2AlCl3(aq) + 3H2(g)
H2SO4(aq) + Zn(s) ZnSO4(aq) + H2 (g)
Acid + active metal
Acid + active metal
Practice1. ID the type, complete, and
balance these reactions involving acids and bases.
c) nitric acid + potassium hydroxide
d) calcium oxide + water
Acid + base (neutralization)
Metal oxide + water
HNO3(aq) + KOH(aq) KNO3(aq) + H2O(l)
CaO(s) + H2O(l) Ca(OH)2(aq)
III. Strength of Acids and Bases
A. Ionization•acids will form ions (electrolytes) when dissolved in water in a process called ionization.
EX:HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)
Bases
•Bases also will form ions (electrolytes) when dissolved in a process called dissociation.
EX: NaOH(s) Na+(aq) + OH-(aq)H2O
•One way to measure the strength of an acid or a base is to measure how much of the original molecule remains after it has been added to water. If little remains, the acid or base is strong. If a lot of the original molecule remains, the acid or base is weak.
•For example, when HCl is added to water, nearly all of the HCl molecules are converted to ions.
HCl + H2O H3O+ +Cl-
Strong Acid
•When acetic acid is added to water, most of the acetic acid molecules remain as molecules and only a small portion of the molecules are converted to ions.
Weak Acid
6 H-A
H+
A-
H+
H+
H+
H+
H+
A-
A-
A-
A-A-
STRONG ACI D100 % I ONI ZED I N WATER
6 H-A
A-H+
H-A
H-A
H+
A-
H-A
H-A
WEAK ACI DLI TTLE I ONI ZATI ON I N WATER
A-
H+
water
acid
proton
anion
H-A
6 H-A
H+
A-
H+
H+
H+
H+
H+
A-
A-
A-
A-A-
6 H-A
H+
A-
H+
H+
H+
H+
H+
A-
A-
A-
A-A-
STRONG ACI D100 % I ONI ZED I N WATER
6 H-A
A-H+
H-A
H-A
H+
A-
H-A
H-A
WEAK ACI DLI TTLE I ONI ZATI ON I N WATER
A-
H+
water
acid
proton
anion
H-A
A-
H+
water
acid
proton
anion
H-A
• Do not confuse the terms strong and weak with the terms concentrated and dilute. Strength refers to what % of the original molecules convert to ions in water. Concentrated or dilute refer to how many total moles there are in water.
Strong acids (lots of H+ ions): HCl, HBr, HI, HNO3, H2SO4Highlight the acids that will ionize almost completely in water.
Weak acids (some H+ ions): HF, HCN, HC2H3O2, H2CO3
Strong bases (lots of OH- ions): NaOH, KOH, Ca(OH)2, LiOH, CsOH, RbOH, Sr(OH)2
Highlight the bases that are very soluble in water.
Weak bases (some OH- ions): CH3N2, NH3, NaCN, Mg(OH)2
B. pH Scale
Hydronium vs Hydroxide
•Hydronium H3O+
– A hydrogen ion in water
– H+ + H2O H3O+
– H+ and H3O+ used interchangeably
– For acids
•Hydroxide OH-
– For bases
1. Background•Any aqueous solution contains both hydronium ions and hydroxide ions. This stems from the fact that water will ionize to a very small amount:
Note: for pure water, the number of hydronium ions is
equal to the number of hydroxide ions.
H2O(l) + H2O(l) H3O+(aq) + OH-(aq)
•when an acid is added to water, the number of hydronium ions increases
HCl(aq) + H2O(l) H3O+(aq) + Cl-
(aq)
•when a base is added to water, the number of hydroxide ions increases
H2O(l)
NaOH(s) Na+(aq) + OH-
(aq)
•it is the ratio of hydronium ions to hydroxide ions that determines whether a solution will be an acid, a base, or neutral
•acid: contains more hydronium ions than hydroxide ions
•base: contains more hydroxide ions than hydronium ions
•neutral: the # of hydronium ions is equal to the # of hydroxide ions
2. pH Scale•a measure of the number of hydronium or hydroxide ions is the pH scale
•it is based on the concentration of hydrogen and hydroxide ions in solution
•pH is defined as the negative logarithm of the hydrogen ion concentration
[ ] = concentration (molarity)
•notice pH is based on a log (base 10) scale
pH = -log([H+])
pH= -log([H3O+])
pH Scale
•the typical pH scale runs from 0 to 14 .
•a pH of 7 is considered neutral which means that the concentration of hydrogen ions and the concentration of hydroxide ions are equal
•as you go down on the pH scale (< 7), solutions are considered acidic
•solutions with pH’s greater than 7 are considered basic
Summary of the pH scale
pH Category Concentration of ions
< 3 strong acid
many H3O+
3-7 Weak acid H3O+ > OH-
7 neutral H3O+ = OH-
7-11 Weak base H3O+ < OH-
> 11 strong base
many OH-
Practice1. Determine whether the following are
a strong acid, a weak acid, a strong base, a weak base, neutral solution
a. pH = 2.5b. lots of hydroxide ions, hardly any hydronium ions
c. little more hydroxide ions than hydronium ions
Strong acid
strong Base
Weak base
•There is also something called pOH, which is a measure of the concentration of hydroxide ions.
pOH = -log ([OH-]
•pH and pOH are related by the following:
14 = pH + pOH
•Again, for strong, single hydroxide bases, [OH-] = molarity of the base.
Ex: What is the pOH of KOH if the pH is 14?
pH + pOH = 1414 + pOH = 14
pOH = 0
Practice1. Determine whether the following
are a strong acid, a weak acid, a strong base, a weak base, neutral solution
pOH = 2.5
12.0 M NaOH
pH = 11.5strong base
pOH = 1.07pH = 12.9strong base
IV. Titrations
A. Titrations
•The concentration of an acid (or base) in solution can be determined by performing a neutralization reaction.
acid + base salt + water
•An indicator is used to show when neutralization has occurred.
•An indicator is a substance that forms different colors in different pH solutions. Phenolphthalein is a common indicator used in acid-base titrations. It will change from colorless in acidic environments to pink in basic environments.
Acid Base Indicators(pH sensitive)
Litmus paper
Acid Base Indicators(pH sensitive)
pH paper
Acid Base Indicators(pH sensitive)
Universal Indicator
Acid Base Indicators(pH sensitive)
Phenolphthalein
Acid Base Indicators(pH sensitive)
Red Cabbage Juice
• The solution of known concentration is called the standard solution. The standard solution is added using a buret.
• The process of adding a known amount of solution of known concentration to determine the concentration of another solution is called titration.
• The point at which the indicator changes color is the end point of the titration.
50
40
30
20
10
0
Titrant- standarized base in burette
Titrand-unknown acid containing indicator and a means f or stirring
Informal titration
•This can also be done less “formally” using any volume measures. The results won’t be as accurate, but it gets you close.
•Example: (drops, substitute for mL)
Steps in a formal titration1. A measured volume
of a solution of unknown concentration (acid or base) is added to an Erlenmeyer flask.
2. A solution of known molarity (acid or base) is added to a buret.
Known MV measured
Known VUnknown M
3. Several drops of an indicator are added to the unknown solution
4. Measured volumes of a solution of known molarity (acid or base) are mixed into unknown solution until the indicator just barely changes color to pink.
Known MV measured
Known VUnknown M
The end point
Phenolphthalein indicator
Clear = Acid Pink = Base
How to read a buret
•This can also be done less “formally” using any volume measures. The results won’t be as accurate, but it gets you close.
Example: (drops, substitute for mL)
B. Solving Titration Problems
Remember, in order for the solution to be neutral,
V = volumeM = molarity (M)A = acidB = base
If the ratio of H+ to OH- is 1:1, then
MAVA = MBVB
(similar to dilutions)
1) It takes 26.23 mL of a 1.008 M NaOH solution to neutralize 35.28 mL of a monoprotic acid solution. What is its molarity?
MA = ? M MB = 1.008 M
VA = 35.28 mL VB = 26.23 mL
MAVA = MBVB
MA(35.28 mL) = (1.008 M) (26.23 mL)
MB = 0.749 M
1.008 M Base
35.28 mL of ?? M acid
Keep adding base until there
is a color change.
Volume of base added = 26.23 mL
2) If 15.50 mL of Ca(OH)2 solution were neutralized with 23.40 mL of 0.533 M H2SO4, what is the concentration of the Ca(OH)2 ?
MA = 0.533 M MB = ? M
VA = 23.40 mL VB = 15.50 mL
MAVA = MBVB
(0.533 M)(23.40 mL) = MB (15.50 mL)
0.805 M = MB
Ex 3: 25.00 mL of 0.720 M nitric acid (HNO3) is used to completely neutralize a 1.0 M NaOH solution. What volume of NaOH is present?
MA = 0.720 M MB = 1.0M
VA = 25mL VB = ??
MAVA = MBVB
(0.720 M)(25 mL) = (1.0 M) VB
18.00 mL = VB
Practice Box Answers
1) 0.385 M H3PO4
2) 5.76 x 10-3 M NaOH3) 0.840 M NaOH4) 55.6 mL H2CO3
1. What is the molarity of phosphoric acid if 15.0 mL of the solution is completely neutralized by 38.5 mL of 0.150 M Al(OH)3?
H3PO4 Al(OH)3
MA = ?? MB = 0.150MVA = 15mL VB = 38.5mL
MAVA = MBVB
MA(15mL) = (0.150M)(38.5mL)
MA = 0.385M H3PO4
2. It takes 26.23 mL of a 0.01 M NaOH solution to neutralize a 45.56 mL of a HCl solution. What is the concentration of the acid?
HCl NaOH
MA = ? MB = 0.01M
VA = 45.56 mL VB = 26.23 mL
MAVA = MBVB
MA(45.56 mL) = (0.01 M)(26.23 mL)
MA = 5.76 x 10-3 M HCl
3. What is the molarity of potassium hydroxide if 20.0 mL of the solution is neutralized by 28.0 mL of 0.60 M HCl?
HCl NaOHMA = 0.60M MB = ??
VA = 28.0mL VB = 20.0mL
MAVA = MBVB
(0.60M)(28.0mL) = MB(20.0mL)0.840M NaOH = MB
4. How many mL of 0.45 M HCl must be added to 25.0 mL of 1.00 M KOH to make a neutral solution?
HCl KOH
MA = 0.45 M MB = 1.00 M
VA = ?? VB = 25.0 mL
MAVA = MBVB
MA(0.45 mL) = (1.00 M)(25.0 mL)
MA = 55.6 mL HCl