chemistry
DESCRIPTION
Class X notesTRANSCRIPT
Acid, Bases, and SaltsChemistry—Part 1
I. Acids
H is a nonmetal or polyatomic ion could be Cl- , SO4
2-, etc.
Ex: HCl, HF, H2SO4 , HClO4, H3PO4
Acids (con’t)
dissociate to form H+ ions (protons)
Hydrogen Atom Hydrogen Ion (proton)
+
e-
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-
+-
Try This:
H2SO4 + H2O
H3PO4 + H2O
SO42-
+
+
SO42-
2 H3O+ + SO42-2
3 H3O+ + PO43-3
B. Examples
Soda pop – H2CO3, H3PO4
Vinegar (acetic acid) – HC2H3O2
Lemons – citric acid Stomach acid – HCl Battery acid – H2SO4
Sour Patch Kids – Tartaric Acid
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
II. Bases
contain OH- (hydroxide ions)Ex: Ca(OH)2, LiOH, NH4OH, NaOH
Also called alkaline (alkali)
Alkali FlatsBonneville Salt Flats, Utah
A. Ionization In Water
NaOH Na+ + OH-
NH4OH
Ca(OH)2
H2O
H2O
H2O
NH4+ + OH-
Ca2+ + 2 OH-
B. Examples
Drano – NaOH Oven cleaner – KOH Tums – Ca(OH)2
Glass cleaner – NH4OH
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
III. Reactions of Acids and Bases
Neutralization:
Acid + Base Salt + Water
HBr + NaOH
Type of reaction? DOUBLE DISPLACEMENT!
NaBr + H2O
Try This:
HF + LiOH
H2SO4 + KOH
HOH + LiF(H2O)
H2O + K2SO42 2
Antacids
Neutralize stomach acid
Ex: TumsHCl + Ca(OH)2
Milk of Magnesia (demo)HCl + Mg(OH)2
H2O + CaCl22 2
H2O + MgCl22 2
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
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
Conductivity Demo
NH4OH + HC2H3O2
Weak Base
Weak Acid
H2O + NH4C2H3O2
Salt
Practice
Salt Parent Acid Parent Base
LiBr
K2CO3
(NH4)2SO4
HBr
H2CO3
H2SO4 NH4OH
KOH
LiOH
H? ?OH
Lab 49 Pre - LabNaCl FeCl3 C6H12O6
Na+ (aq) + Cl- (aq) Fe3+ (aq) + 3 Cl- (aq)
C6H12O6 (aq)
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
1. Ternary Acidscontain THREE elements
(usually)contain H and a polyatomic ion
ate ic ite ousex: H2CO3 carbonate carbonic
Carbonic Acid
Try TheseHNO2
nitrite nitrousNitrous Acid
HNO3
nitrate nitricNitric Acid
H2SO3
sulfite sulfurousSulfurous Acid
H2SO4
sulfate sulfuricSulfuric Acid
Base Names (IUPAC Nomenclature)
Combine names of ions
NaOHSodium Hydroxide
Ca(OH)2
Calcium Hydroxide
Salt Names
Combine names of ions
NaBrSodium Bromide
K2SO4
Potassium SulfateCu(NO3)2
Copper (II) Nitrate
VI. Salts
Salts are ionic and crystalline
A. Dissociation in Water
Salt Cation + Anion
LiCl
Na2SO4
H2O
H2O
H2O
Li+ + Cl-
2 Na+ + SO42-
B. Cation and Anion
Cation: Positive (+) charge
The ___________ contributes the cation(acid/base?)
Anion: Negative (-) charge
The ___________ contributes the anion(acid/base?)
C. Examples
Cation Anion
NaCl
NaHCO3
K2SO4
Na+
K+
Na+
SO42-
HCO3-
Cl-
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
VIII. Strong Acids and Bases
STRONG ACIDS—DISSOCIATE 100 %HCl HNO3 H2SO4
STRONG BASES—DISSOCIATE 100%All Alkali Metals (IA) form strong
bases
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?
IX. Polyprotic Acids
Acids with more than one proton (H+)
A. Examples
H2SO4 H3AsO4 H3PO4 H2CO3 H2S
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
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+)
Lab 50 Answers
Water as an acid and a base
amphoteric:
water behaves as an acid & base
H2O + H2O H3O+ + OH-
acid base conj conj
acid base
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
Basic Anhydrides—metal oxides that combine with H2O to form a base
CaO + H2O Ca(OH)2
Na2O + H2O
Basic Anhydrides
2 NaOH
Try These: Acidic or Basic Anhydride?
K2O
Basic Anhydride
NO2
Acidic Anhydride
http://www.epa.gov/maia/images/acid.jpg
Acid, Bases, and Salts
Chemistry—Part 2
I. Molarity
Example: 6 KOH 0.1 H2SO4 2 NaCl
A measure of concentration
solution
moles #
LM
M M M
Concentration
6 M 1 M
Examples
3 M HNO3 =
solution L 1
HNO moles 3 3
ML
moles4
5
20
20 moles in 5 L = ? M
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
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
II. Titration
Using a solution of to determine the concentration of another solution.
A neutralization reactionAcid + Base
known concentration
Salt + Water
End Point
The point at which neutralization is complete
moles H+ = moles OH-
use (like phenolphthalein) to determine the end point
acid-base indicators
Acidic—before neutralization
Neutral—”End Point”
Basic—“overshot endpoint”
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-
NaOH Na+ + OH-
HCl H+ + Cl-
1 M 1 M
2 M2 M
50 ml
25 ml
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!!!
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+)
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+)
III. IndicatorsWeak organic acids or bases that are a
different color in an acid than in a base
Ex:PhenolpthaleinBromothymol BlueLitmusRed Cabbage
Limitations of Indicators
Solutions must be colorless
Eye must be able to detect the change
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
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?
Example #1
[OH-] = 10-6 M [H+] = ?
MH
H
OHHKw
8
614
10][
]10][[10
]][[
Example #2
[H+] = 10-3 M [OH-] = ?
MOH
OH
OHHKw
11
314
10][
]][10[10
]][[
pH Scale
Used to measure acidity
Based on the concentration of H+ ions
When the [H+] increases by 10, the pH decreases by 1.
When the pH increases by 2, the [H+] decreases by _____102 = 100
pH = -log[H+]
[H+] = 10-4 pH = ______ acidic or basic?
[H+] = 10-11 pH = ______ acidic or basic?
4
11
pOH = -log[OH+]
[OH-] = 10-3 pOH = ______
[H+] = 10-9 pOH = ______
3
5
pH + pOH = 14
Why?[H+] [OH-] = 10-14
(10-7) (10-7) = 10-14
pH + pOH = 14
- log - log
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+]?
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
Look at the Parent Acid & Parent Base
Salt Parent Acid Parent Base
Neutral STRONG STRONG
Acidic STRONG weak
Basic weak STRONG
Ex: NaF
Parent Acid:
Parent Base:
So…NaF is BASIC
HF
NaOH
strong or weak?
strong or weak?
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?
Try This: NaCl
Parent Acid:
Parent Base:
So…NaCl is NEUTRAL
HCl
NaOH
strong or weak?
strong or weak?