chemical reactions.equilibrium.acids&bases
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Chemical
Reactions.
Equilibrium.
Acids &Bases
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Oxidation Number
Charge of an atom or a group of atoms
Also known as Valence
Ex: NaCl, Na+ and Cl-
H2SO4, H+, S+6 and O-2
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Writing formulas When the oxidation numbers of the atoms in a
compound are known, we can write the chemical formula of that compound. Ex: H+ and O 2- form H2O (sum of oxidation
numbers in a neutral compound should be 0)
When knowing the formula of a chemical compound, we can find the oxidation numbers of the atoms in that compound. Ex: H2SO4 H always +1, O always +2, so
2x (+1) + 4x (-2) = -6. Since H2SO4 is neutral, S has to be +6.
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Chemical Reactions
5 types:
1. Combination Reactions
2. Combustion Reactions
3. Decomposition Reactions
4. Single-replacement Reactions
(Displacement)
5. Double-replacement Reactions
(Metathesis)
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Combination Reactions
formation of a compound from two or
more substances
Ex:
2Na (s) + Cl2 (g) 2NaCl (s)
CO2 (g) + H2O (l) H2CO3 (l)
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Combustion Reactions
reaction of substances with O2 usually accompanied by the release of
large amounts of heat (Q)
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Decomposition Reactions
one compound decomposes or splits to
form two or more simpler compounds
and/or elements.
Ex:
CaCO3 (s) CaO (s) + CO2 (g)
H2CO3 (l) H2O (l) + CO2 (g)
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Single-replacement Reactions
An element reacts with a compound, and
results in the displacement of an element
or group from the compound.
Ex:
Na(s) + HOH (l) NaOH (aq) + H2 (g)
Na (s) + HCl (g) NaCl (s) + H2 (g)
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Double-replacement
Reactions
exchange of two groups or two ions
among the reactants
Ex:
NaOH (aq) + HCl (aq) NaCl (aq) + HOH(l)
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Balancing Simple Equations Ex: 4Al+ 3 O2 2 Al2O3
Al=1 x4= 4 Al=2 x2= 4
O=2 x 3= 6 O=3x2 = 6
2Na + H2SO4 Na2SO4 + H2
Na=1x2=2 Na=2
H=2 H=2
S=1 S=1
O=4 O=4
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Oxidation-Reduction
Reactions
Oxidation-reduction (redox) reactions
involve the transfer of electrons from one
compound or species to another.
Oxidation is the process by which an
atom or species loses its electrons.
Reduction is the process by which an
atom or species gains electrons.
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Oxidation-Reduction
Reactions
Ex:
2Fe + 3Cl2 2 FeCl3
Fe0 Fe3+ + 3e- oxidizing 3 2
6
2Cl0 + 2x 1 e-2 Cl- reducing 2 3
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Oxidation-Reduction
Reactions
Ex:
3Cu0 + 8H+N+5O3-2 3Cu+2(N+5O3
-2)2-1 + 2N+2O-2 +
4H+2O-2
Cu0 Cu+2 + 2 e- 2 3
6
N+5 + 3 e- N+2 3 2
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Solutions Solution = one solvent with one or more
solutes.
Mixing states or same state
Water-based solutions: the solvent is water.
Solubility=the amount of the substance that will dissolve in a particular solvent.
"like dissolves like : water is polar, will dissolve polar or ionic
substances
Non-polar substances will be soluble in non-polar solvents (ex CCl4)
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Solutions
Concentration:
c%=
x 100 (%)
md= mass of dissolved substance (g),
ms=mass of solution (g)
Molarity
C=
(moles/l, M) ,
=nr. of moles,
V=volume of the solution (l)
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Solutions
Molality
C=
(moles/kg)
=nr. of moles,
ms=mass of the solvent (kg)
Normality
CN =
(Eg/l) CN=nxCM
Eg= gram equivalents n is nr. of H+, OH-, e-
V=volume of solution
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Equilibrium
Reversible reactions are reactions in
which there are both forward and
backward reactions.
Ex:
CH3OH+ CH3COOH CH3COOCH3 + H2O
back-and-forth directional changes take
place until the reaction mixture reaches
the equilibrium!
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Equilibrium
equilibrium constant (Kech) of a reversible
reaction is equal to the ratio of the
product of the concentrations of the
products raised to their corresponding
coefficients, to the product of the
concentrations of the reactants raised to
their corresponding coefficients.
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Ex:
a A+ b B c C + d D
Kech=
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Le Chateliers Principles lf we change the conditions factors
(concentration, pressure, temperature) of a reaction system in equilibrium, the system will shift in such a way as to reduce the imbalance caused by the stress.
Ex: N2 (g) + 3H2(g) 2 NH3 (g) + Q A raise in concentration of N2 will shift the
system to the right
A raise in pressure will shift the system to the right
A raise in temperature will shift the system to the left
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Acid-Base Equilibrium 3 theories:
Arrhenius Definition:
Acid increases H+ ions in an aqueous solution
Base increases OH- ions in an aqueous solution
The Bronsted-Lowry Definition
acid proton donor,
base proton acceptor.
The Lewis theory
Lewis acid accepts a pair of electrons
Lewis base donates a pair of electrons
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Ex:
Hl + H20 H3O+ + l- (gives protons)
Acid Conjugated
Base
NH3+H2O 4++ HO- (accepts protons)
Base Conjugated
Acid
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Concept of pH
pH shows the acidity of a solution and is
defined as log [H3O+]
pOH is complementary, and shows the
basicity of a solution and is defined as
log[HO-]
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Ionization of water
H2O + H2O H3O+ + HO-
Kech = 3
+[
]
22 , but since H2O is
considered constant, Kechx[H2O]
2=Kw=[H3O+][HO-], Kw is defined
as the ion-constant product of water, and
has the value of 10-14 (mol/l)2
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When we apply a logarithm to the
expression we get:
log Kw = log [H3O+]+ log [HO-].
If we multiply by (-1), we get:
-log Kw = - log [H3O+]+ (- log [HO-]),
So 14= pH + pOH.
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Strong Acids. Strong Bases Strong acid= one way reaction (not
equilibrium)
HA+H2O H3O+ + A-
pH= - log [H3O+] = -log CHA
Strong base= one way reaction (not equilibrium)
B+H2O OH-+ BH+
pOH= - log [HO-] = -log CB Ex: strong acids: HCl, H2SO4 strong bases: NaOH, KOH
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Weak Acids
Weak acid= equilibrium reaction
HA+H2O H3O+ + A-
Kech= 3
+[]
2 [] , since we can consider [H2O]
constant,
Kechx[H2O]=Ka= 3
+[]
[], where Ka is the acidity
constant.
Ex: citric acid (lemon), acetic acid (vinegar)
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Weak Acids pH = - log [H3O
+]
[H3O+]=
[]
[]
, but [H3O+]= [A-],
So [H3O+]2=Kax[HA]
[H3O+]=
pH= -log
pH=-1
2logKaxCHA
pH= -1
2 log Ka -
1
2 log CHA
-log Ka= pKa,
So pH=
pKa -
log CHA
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Weak bases
Weak base= equilibrium reaction
B+H2O BH+ + OH-
Kech=
+[
]
2 [] , since we can consider
[H2O] constant,
Kechx[H2O]=Kb=
+[
]
[], where Kb is the
basicity constant.
Ex: ammonia, NH4OH.
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Weak Bases pOH = - log [HO-]
[HO-]= []
[+], but [HO-]= [BH+],
So [HO-]2=Kbx[B]
[HO-]=
pOH= -log
pOH=-1
2logKbxCB
pOH= -1
2 log Kb -
1
2 log CB
-log Kb= pKb,
So pOH=
pKb -
log CB
pH+pOH=14,
So pH= 14- (
pKb -
log CB )
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Buffer Solutions
solutions which resist changes in pH when small amounts of acid or base are added
usually a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.
Ex: plasma is a buffer solution (complex system with more than one acid/base, the most important one being the H2CO3/HCO3
- couple)
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For a weak acid-conjugated base:
pH=pKa+log[ ]
[ ]
For a weak base-conjugated acid:
pOH=pKb+log[ ]
[ ]
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