22 acids + bases

ACIDS• Properties: (other than tasting sour and being
corrosive)
1) React with metals
2) React with carbonates
3) Conduct electricity
4) Turn blue litmus paper red
5) Neutralize bases
ACIDS ARE CORROSIVE

1) ACIDS REACT WITH METALS
If you swallowed a penny,
what would happen?
(DON’T TRY THIS AT HOME!!!)

1) ACIDS REACT WITH METALS
2HCl(aq) + Zn(s)  H2(g) + ZnCl2(aq)

2) ACIDS REACT WITH CARBONATES
What happens when you put baking soda
(sodium bicarbonate) into vinegar?
HC2H3O2(aq) + NaHCO3(aq)  CO2(g) + H2O(l) + NaC2H3O2(aq)

3) ACIDS CONDUCT ELECTRICITY
Acids are made of ions, so in water these ions
separate and can conduct electricity
HCl(aq)  H+
(aq) + Cl-
(aq)

IONIZATION IN WATER
H+
Cl-
H+
Cl-
H+
Cl-
Strong acids
ionize completely
in water, while
weak acids only
ionize slightly

NEGATIVELY-CHARGEDELECTRODE
POSITIVELY-CHARGEDELECTRODE
IONIZATION IN WATER
H+
Cl-
H+Cl-
H+
Cl-
H+
Cl-
- +

4) ACIDS TURN BLUE LITMUS PAPER RED
Blue litmus paper is an indicator and turns red when
it touches acid

5) ACIDS NEUTRALIZE BASES
Acids can neutralize bases, so adding an acid to a
base can eliminate their corrosiveness
HCl(aq) + NaOH(aq)  H2O(l) + NaCl(aq)
Hydrochloric acid + sodium hydroxide  water + salt (sodium chloride)
Corrosive + corrosive  non-corrosive + non-corrosive

BASES
Properties: (other than tasting bitter, feeling slippery)
1) Conduct electricity
2) Turn red litmus paper blue
3) Neutralize acids
BASES ARE CAUSTIC

1) BASES CONDUCT ELECTRICITY
Bases are made of ions, so in water these ions
separate and can conduct electricity
NaOH(aq)  Na+
(aq) + OH-
(aq)

2) BASES TURN RED LITMUS PAPER BLUE
Red litmus paper is an indicator and turns blue when
it touches base

3) BASES NEUTRALIZE ACIDS
Bases can neutralize acids, so adding a base to an acid can
eliminate their corrosiveness
Example: Antacids to neutralize stomach acid
2HCl(aq) + CaCO3(aq)  CaCl2(aq) + H2CO3(aq)
H2CO3(aq)  H2O(l) + CO2(g)

HOW TO MAKE ACIDS + BASES
ACIDS:
1) Non-metal + oxygen  non-metal oxide
2) Non-metal oxide + water  ACID!
EXAMPLE:
N2 + 2O2  2NO2
NO2 + H2O  HNO3
BASES:
1) Metal + oxygen  Metal oxide
2) Metal oxide + water  BASE!
EXAMPLE:
Mg + O2  MgO
MgO + H2O  Mg(OH)2

ACID-BASE INDICATORS
Indicators change color depending on whether a substance is
acidic or basic

pH Scale
From 1 to 14, with 7 being NEUTRAL

Arrhenius Theory of Acids and Bases
An acid is a substance that dissociates in
water to produce one or more hydrogen
ions (H+
)
ex. HBr(aq)  H+
(aq) + Br-
(aq)
A base is a substance that dissociates in
water to form one or more hydroxide ions
(OH-
)
ex. LiOH(aq)  Li+
(aq) + OH-
(aq)

My theory has a
limitation…
HBr(aq)  H+
(aq) + Br-
(aq)
This reaction takes place in water!
Without water, acid properties and
reactions can’t exist.
A hydronium ion is actually
produced (H3O+
) to enable the
effects of water.
HBr(aq) + H2O(l)  H3O+
(aq) + Br-
(aq)
Arrhenius’s theory
does not account for
the hydronium ion

…more like 2
limitations…
NH3(aq) is a base
and does NOT have OH!!!!
Actual reaction:
NH3(aq) + H2O(l)  NH4
+
(aq) + OH-
(aq)
Arrhenius’s theory does not account for
bases without OH groups

Brønsted-Lowry Theory of Acids and Bases
An acid is a
substance from which
a proton (H+
ion) can
be removed
A base is a substance
that can remove a
proton (H+
ion) from
an acid

H2O(l) + HCl(aq)  H3O+
(aq) + Cl-
(aq)
Two molecules or ions that are related by the transfer of a
proton are called a conjugate acid-base pair
Conjugate acid-base pair

HBr(g) + H2O(l)  H3O+
(aq) + Br-
(aq)
Examples of conjugate acid-base pairs

NH3(g) + H2O(l)  NH4
+
(aq) + OH-
(aq)
Examples of conjugate acid-base pairs

Strong and Weak Acids
Strong acid/base: dissociates completely in water
Examples: HCl, H2SO4 NaOH, Ba(OH)2
Weak acid/base: dissociates very slightly in water
Examples: CH3OOH (acetic acid) NH3
Conjugate acid-base pair Reversible…at equilibrium

Monoprotic acid: Acid only has one hydrogen ion
Ex: HCl
Diprotic acid: Acid has two hydrogen ions
Ex: H2SO4
Triprotic acid: Acid has three hydrogen ions
Ex: H3PO4
ACIDS

Looking at a triprotic acid…
H3PO4
First ion dissociates: H3PO4(aq) + H2O(l) H3O+
(aq) + H2PO4
-
(aq)
Second ion dissociates: H2PO4
-
(aq) + H2O(l) H3O+
(aq) + HPO4
2-
(aq)
Third ion dissociates: HPO4
2-
(aq) + H2O(l) H3O+
(aq) + PO4
3-
(aq)
STRONGEST acid (easiest to dissociate)
WEAKEST acid (hardest to dissociate)
ACIDS

If the pH is greater than 7,
then the substance is basic
If the pH is less than 7, then
the substance is acidic
NEUTRAL
Power of Hydrogen (pH)

H2O(l) + H2O(l) H3O+
(aq) + OH-
(aq)
[H3O+
] = [OH-
] = 1.0 x 10-7
mol/L
In a neutral solution at 25ºC…
Concentration of H3O+
Concentration of OH-
pH
Negative
logarithm of…
Or
-log
Concentration
of H3O+
ions
(in mol/L)
Or
[H3O+
]

Therefore pH of water = -log [H3O+
]
= -log [1.0x10-7
]
= -(-7.00)
= 7.00

pH = - log [H3
O+
]
pOH = - log [OH-
]
[H3
O+] = 10 –pH
[OH-] = 10-pOH
pH + pOH = 14
Formulae involving pH:

pOH = -log [OH-
]
= -log [3.8x10-3
]
= 2.42
pH = 14 – pOH
= 14 – (2.42)
= 11.58
= 12
Calculate the pH of a solution with [OH-
] = 3.8x10-3
mol/L
HOMEWORK: Page 393 #8, 9

CALCULATIONS INVOLVING
NEUTRALIZATION REACTIONS
Stoichiometry calculations:
1) Write the balanced chemical reaction
2) Convert all measurements to moles (if you can)
3) Work with molar ratios to find out how much an acid is needed
to neutralize a given amount of base, or vice versa.
HCl(aq) + NaOH(aq)  H2O(l) + NaCl(aq)
For example:
How many moles of HCl would you need to neutralize 2 moles of NaOH?
ANSWER: 2 moles of HCl

What volume of 0.250 mol/L H2SO4(aq) is needed to react
completely with 37.2mL of 0.650mol/L KOH(aq)?

H2SO4(aq) + 2KOH(aq) 2H2O(l) + K2SO4(aq)
Step 1: Write the balanced chemical reaction
Step 2: Convert everything to moles
nKOH = C x V
= (0.650mol/L) x (0.0372L)
= 0.02418mol KOH
Step 3: Work with molar ratios
1mol H2SO4 = x
2mol KOH 0.02418mol KOH
x = 0.01209mol H2SO4
NOT DONE YET! Need to solve for volume of H2SO4

V = n/C
= (0.01209mol)/(0.250mol/L)
= 0.04836L H2SO4
Therefore the volume of H2SO4 needed is 48.4mL
HOMEWORK: Page 398 #13 + Page 406 #15

New Acid-Base TheoryNew Acid-Base Theory

Lewis Acids and BasesLewis Acids and Bases
Identify the acids and bases.
H2SO3(aq) + Ca(OH)2(aq)  CaSO3(s) + 2 H2O
Identify the acid and base.
CaO(s) + SO2(g)  CaSO3(s)
Are the two reactions the same?
acid base
Lewis acidLewis base

Lewis Acids and BasesLewis Acids and Bases
Not all acid-base reactions involve proton
transfer.
acid – chemical substance that can accept a
pair of electrons to form a covalent bond
base – chemical substance that can donate a
pair of electrons to form a covalent bond
neutralization – formation of a covalent bond
between an acid and base reactant

Example #1Example #1
a) H+
(aq) + OH-
(aq) <===> H2O(l)
b) NH3 + BCl3  ?
Lewis acid Lewis base
BCl3:NH3
adduct: often formed between Lewis acids and bases, resulting
in a single product containing all atoms of all components.

ExamplesExamples
c) sulfur dioxide + oxide ion  sulfite ion
d) Identify the Lewis acid and base given:
OH-
+ CO2  HCO3
-
SO2 + O2-
 SO3
2-
Lewis acid Lewis base

22 acids + bases

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