chemistry
DESCRIPTION
Class X notesTRANSCRIPT
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Acid, Bases, and SaltsChemistry—Part 1
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I. Acids
H is a nonmetal or polyatomic ion could be Cl- , SO4
2-, etc.
Ex: HCl, HF, H2SO4 , HClO4, H3PO4
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Acids (con’t)
dissociate to form H+ ions (protons)
Hydrogen Atom Hydrogen Ion (proton)
+
e-
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A. Ionization in Water
HCl + H2O
H+ combines with H2O to form H3O+
Hydronium Ion
H+(proton) is attracted to lone e- pairs in H2O
H3O+ + Cl-
+-
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Try This:
H2SO4 + H2O
H3PO4 + H2O
SO42-
+
+
SO42-
2 H3O+ + SO42-2
3 H3O+ + PO43-3
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B. Examples
Soda pop – H2CO3, H3PO4
Vinegar (acetic acid) – HC2H3O2
Lemons – citric acid Stomach acid – HCl Battery acid – H2SO4
Sour Patch Kids – Tartaric Acid
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C. Properties
taste sour conduct electricity turn litmus red react with some metals to produce H2
(g) Remember, Zn + 2HCl ZnCl2 + H2(g)
corrosive All form H+ ions in solution
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II. Bases
contain OH- (hydroxide ions)Ex: Ca(OH)2, LiOH, NH4OH, NaOH
Also called alkaline (alkali)
Alkali FlatsBonneville Salt Flats, Utah
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A. Ionization In Water
NaOH Na+ + OH-
NH4OH
Ca(OH)2
H2O
H2O
H2O
NH4+ + OH-
Ca2+ + 2 OH-
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B. Examples
Drano – NaOH Oven cleaner – KOH Tums – Ca(OH)2
Glass cleaner – NH4OH
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C. Properties
Taste bitter (Baking Soda) Conduct electricity Turn litmus blue Feel slippery (hard to wash off of skin) Caustic (dissolves protein, ie. YOU) Form OH- ions
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III. Reactions of Acids and Bases
Neutralization:
Acid + Base Salt + Water
HBr + NaOH
Type of reaction? DOUBLE DISPLACEMENT!
NaBr + H2O
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Try This:
HF + LiOH
H2SO4 + KOH
HOH + LiF(H2O)
H2O + K2SO42 2
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Antacids
Neutralize stomach acid
Ex: TumsHCl + Ca(OH)2
Milk of Magnesia (demo)HCl + Mg(OH)2
H2O + CaCl22 2
H2O + MgCl22 2
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IV. Electrolyte Solutions
Substances whose water solutions conduct electricity
NaCl (c) vs. NaCl (aq) Sucrose (c) vs. Sucrose (aq) H2O (distilled) vs. H2O (tap)
There must be ions present to conduct
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Strong & Weak Electrolytes
STRONG ELECTROLYTES
Ionize 100%NaCl
WEAK ELECTROLYTES
Only partially ionizeHF
Na+ + Cl-
H+ + F-
Na+
Na+Cl-
Cl-
NaCl (s)
HF (s)
HF
HFHF
H+
F+
only ions are present
mostly HF present;only some ions
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Conductivity Demo
NH4OH + HC2H3O2
Weak Base
Weak Acid
H2O + NH4C2H3O2
Salt
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Practice
Salt Parent Acid Parent Base
LiBr
K2CO3
(NH4)2SO4
HBr
H2CO3
H2SO4 NH4OH
KOH
LiOH
H? ?OH
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Lab 49 Pre - LabNaCl FeCl3 C6H12O6
Na+ (aq) + Cl- (aq) Fe3+ (aq) + 3 Cl- (aq)
C6H12O6 (aq)
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V. Naming Acids, Bases & Salts
Acid Names1. Binary Acids
contain only TWO elementsex: HCl Hydrochloric Acid Hydro-stem-ic AcidTry: HBr
HFH2S
Hydrobromic AcidHydrofluoric AcidHydrosulfuric Acid
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1. Ternary Acidscontain THREE elements
(usually)contain H and a polyatomic ion
ate ic ite ousex: H2CO3 carbonate carbonic
Carbonic Acid
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Try TheseHNO2
nitrite nitrousNitrous Acid
HNO3
nitrate nitricNitric Acid
H2SO3
sulfite sulfurousSulfurous Acid
H2SO4
sulfate sulfuricSulfuric Acid
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Base Names (IUPAC Nomenclature)
Combine names of ions
NaOHSodium Hydroxide
Ca(OH)2
Calcium Hydroxide
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Salt Names
Combine names of ions
NaBrSodium Bromide
K2SO4
Potassium SulfateCu(NO3)2
Copper (II) Nitrate
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VI. Salts
Salts are ionic and crystalline
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A. Dissociation in Water
Salt Cation + Anion
LiCl
Na2SO4
H2O
H2O
H2O
Li+ + Cl-
2 Na+ + SO42-
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B. Cation and Anion
Cation: Positive (+) charge
The ___________ contributes the cation(acid/base?)
Anion: Negative (-) charge
The ___________ contributes the anion(acid/base?)
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C. Examples
Cation Anion
NaCl
NaHCO3
K2SO4
Na+
K+
Na+
SO42-
HCO3-
Cl-
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Parent Acid / Parent Base
Parent Acid: The acid that contributes the ANION to the salt
Parent Base: The base that contributes the CATION to the salt
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VIII. Strong Acids and Bases
STRONG ACIDS—DISSOCIATE 100 %HCl HNO3 H2SO4
STRONG BASES—DISSOCIATE 100%All Alkali Metals (IA) form strong
bases
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VIII. Weak Acids and Bases
WEAK ACIDS—DO NOT DISSOCIATE 100 %
WEAK BASES—DO NOT DISSOCIATE 100%
How would a weak acid conduct electricity compared to a strong acid?
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IX. Polyprotic Acids
Acids with more than one proton (H+)
A. Examples
H2SO4 H3AsO4 H3PO4 H2CO3 H2S
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B. Step – By – Step Ionization
Acids lose one proton at a time
1st H3PO4
2nd H2PO4-
3rd HPO4-2
H3PO4 3H+ + PO43-
H+ + H2PO4-
H+ + HPO4-2
H+ + PO4-3
H3PO4 + H2O 3 H3O+ + PO43-3
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Questions1. Which of the following are polyprotic
acids?a) HCl d) HC2H3O2
b) NH3 e) H3PO4
c) H2SO4 f) HNO3
2. Which acid is harder to ionize: H3PO4 or HPO4
-2? Why?The -2 charge attracts protons (H+)
3. Which acid is stronger: H2SO4 or HSO4-?
Why?easier to lose protons (H+)
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Lab 50 Answers
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Water as an acid and a base
amphoteric:
water behaves as an acid & base
H2O + H2O H3O+ + OH-
acid base conj conj
acid base
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X. Anhydrides
Without water
Acidic Anhydrides—non-metallic oxides that combine with H2O to form an acid
SO2 + H2O H2SO3
CO2 + H2O
Acid Anhydrides
H2CO3
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Basic Anhydrides—metal oxides that combine with H2O to form a base
CaO + H2O Ca(OH)2
Na2O + H2O
Basic Anhydrides
2 NaOH
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Try These: Acidic or Basic Anhydride?
K2O
Basic Anhydride
NO2
Acidic Anhydride
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http://www.epa.gov/maia/images/acid.jpg
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Acid, Bases, and Salts
Chemistry—Part 2
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I. Molarity
Example: 6 KOH 0.1 H2SO4 2 NaCl
A measure of concentration
solution
moles #
LM
M M M
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Concentration
6 M 1 M
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Examples
3 M HNO3 =
solution L 1
HNO moles 3 3
ML
moles4
5
20
20 moles in 5 L = ? M
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Try This!
If 80 grams of NaOH (MW=40) is dissolved in 2 L, find the molarity.
molesmolg
g2
/40
80 M
L
moles1
2
2
6 moles of HBr in 250 ml. Molarity?
Mxml
xmoles
ml
moles24
1000250
6
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Now Try This One!
How many moles of HCl are in 500 ml of a 3 M solution?
molesxL
xmolesM
L
molesM
5.15.0
3
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II. Titration
Using a solution of to determine the concentration of another solution.
A neutralization reactionAcid + Base
known concentration
Salt + Water
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End Point
The point at which neutralization is complete
moles H+ = moles OH-
use (like phenolphthalein) to determine the end point
acid-base indicators
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Acidic—before neutralization
Neutral—”End Point”
Basic—“overshot endpoint”
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NaOH
HCl
H2SO4
1 M 1 M
1 M1 M
50 ml
50 ml
1 M 2 M25 ml
Na+ + OH-
H+ + Cl-
2 H+ + SO42-
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NaOH Na+ + OH-
HCl H+ + Cl-
1 M 1 M
2 M2 M
50 ml
25 ml
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Titration Equation
OHBBHAA VMVM # #
MA = Molarity of AcidVA = Volume of Acid#H+= Number of H’s in acid formula
MB = Molarity of BaseVB = Volume of Base#OH- = Number of OH’s in base formula
UNITS MUST MATCH!!!
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Try This
50 ml of 0.1 M NaOH is neutralized by 5 ml of HCl. Find the molarity of the acid.
MM
OHmlMHmlM
VMVM
A
A
OHBBHAA
1
)1)(50)(1.0()1)(5)((
# #
(5ml)(1H+) (5ml)(1H+)
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Try This
40 ml of 1M KOH is neutralized by 10 ml of sulfuric acid. Find the molarity of acid.
MM
OHmlMHmlM
VMVM
A
A
OHBBHAA
2
)1)(40)(1()2)(10)((
# #
(10ml)(2H+) (10ml)(2H+)
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III. IndicatorsWeak organic acids or bases that are a
different color in an acid than in a base
Ex:PhenolpthaleinBromothymol BlueLitmusRed Cabbage
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Limitations of Indicators
Solutions must be colorless
Eye must be able to detect the change
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IV. Ionization of Water
In pure water, [H+] = 10-7 M and [OH-] = 10-7 M
1 water out of 10,000,000 forms ions
[ ] stands for concentration
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Kw – water’s ionization constant
Kw = [H+] [OH-]
Kw = (10-7) (10-7)
Kw = 10-14
so…
10-14 = [H+][OH-]
CONSTANT
Add Acid? Add Base?
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Example #1
[OH-] = 10-6 M [H+] = ?
MH
H
OHHKw
8
614
10][
]10][[10
]][[
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Example #2
[H+] = 10-3 M [OH-] = ?
MOH
OH
OHHKw
11
314
10][
]][10[10
]][[
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pH Scale
Used to measure acidity
Based on the concentration of H+ ions
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When the [H+] increases by 10, the pH decreases by 1.
When the pH increases by 2, the [H+] decreases by _____102 = 100
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pH = -log[H+]
[H+] = 10-4 pH = ______ acidic or basic?
[H+] = 10-11 pH = ______ acidic or basic?
4
11
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pOH = -log[OH+]
[OH-] = 10-3 pOH = ______
[H+] = 10-9 pOH = ______
3
5
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pH + pOH = 14
Why?[H+] [OH-] = 10-14
(10-7) (10-7) = 10-14
pH + pOH = 14
- log - log
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Try These:For a solution that is 0.1 M HCl…1) What is the pH?2) What is the concentration of OH- ions?3) What is the pOH?For a solution that is 0.001 M NaOH…4) What is the pOH?5) What is the pH?6) What is [H+]?For a solution that has a pH of 8…7) What is the [H+]?
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Hydrolysis
The reaction of a salt with water to form an acidic or basic solution
Recall Strong Acids:
Recall Strong Bases:
HCl HNO3 H2SO4
Group IA Hydroxides
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Look at the Parent Acid & Parent Base
Salt Parent Acid Parent Base
Neutral STRONG STRONG
Acidic STRONG weak
Basic weak STRONG
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Ex: NaF
Parent Acid:
Parent Base:
So…NaF is BASIC
HF
NaOH
strong or weak?
strong or weak?
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Try This: Fe(NO3)3
Parent Acid:
Parent Base:
So…Fe(NO3)3 is ACIDIC
HNO3
Fe(OH)3
strong or weak?
strong or weak?
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Try This: NaCl
Parent Acid:
Parent Base:
So…NaCl is NEUTRAL
HCl
NaOH
strong or weak?
strong or weak?