C h a pt e r
14
Hydrogen, Oxygen, and Water
Chemistry 4th Edition
McMurry/Fay
Dr. Paul Charlesworth
Michigan Technological University
Hydrogen (1 H)
•
Isotopes of Hydrogen:
•
Proteum, 1 H
H2O(l) æ H+(aq) + OH–(aq)
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Deuterium, 2H
D2O(l) æ D+(aq) + OD–(aq)
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K = 1.01 x 10–14
K = 0.195 x 10–14
Tritium, 3H Undergoes v decay to 3He + e–.
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1H
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Preparation
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01
Slide 3
1
1H
Preparation
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Steam –hydrocarbon re-forming process:
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1100°C on Nickel Catalyst:
•
400°C in Catalyst:
02
H 2O(g) + CH4(g) → CO(g) + 3 H2(g) ?H° = +206 kJ
CO(g) + H2O(g) → CO2(g) + H2(g) ? H° = –41 kJ
•
Removal of CO2 by basic solution:
CO2(g) + 2 OH –(aq) → CO3 2–(a q) + H2O(l)
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1H
Chemical Properties
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Forms hydride ion (H–) with metals.
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Hydride bonding can be covalent (BH4–, AlH4–).
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Forms covalent bond with nonmetals.
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Can dissociate from nonmetals in water to form
hydrogen ion (H+). Essentially a solvated bare
proton (H3O+).
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1H
Slide 5
Chemical Properties
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Reaction with oxygen
is exothermic
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Equilibrium lies far
to right
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Water formation is
spontaneous
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2
1H
Binary Hydrides
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1H
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Binary Hydrides
01
Slide 7
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Ionic Hydrides:
2 Na(l) + H2(g) → 2 NaH(s) ?H° = –112.6 kJ
Ca(s) + H2(g) → CaH2(s) ?H° = –181.5 kJ
•
Covalent Hydrides: Compounds in which
hydrogen is attached to another element by a
covalent bond.
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1H
Binary Hydrides
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Metallic Hydrides: Formed by
reaction of some d-block and fblock metals with variable
amounts of hydrogen.
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Often called Interstitial Hydrides
because hydrogen occupies
holes in the crystal lattice.
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3
1H
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Binary Hydrides
04a
The following picture represents a binary hydride
AHx, where A = K, Ti, C, or F. Ivory spheres are H.
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1H
Binary Hydrides
Slide 10
04b
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Using the previous image:
1.
Write the formula of each hydride and classify
them as ionic, covalent, or interstitial.
2.
Which has the lowest melting point?
3.
Which reacts with water to give H2 gas?
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1H
Binary Hydrides
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05
Ionic hydrides react with water to give H2(g) and
OH–(aq).
CaH2(s) + 2 H2 O(l) → 2 H2(g) + Ca 2+(aq) + 2 OH–(aq)
Note that this is a redox reaction. Ionic hydrides are
good reducing agents.
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1H
Fuel Cells
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Combine H2 and
O2 to form H2O
and energy.
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Prototype car fuel
cells have enough
excess energy to
power a typical
home.
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Oxygen
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Slide 13
01
46% by mass in the Earth's crust, and 23% in the
atmosphere.
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Oxygen has two allotropes, O2 and O3.
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O2 is paramagnetic because of unpaired electrons.
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Oxygen Preparation
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Electrolysis of Water:
2 H2O(l) → 2 H2(g) + O2(g)
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Decomposition of Hydrogen Peroxide:
2 H2O2(aq) → 2 H2O(l) + O2(g)
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Decomposition of Oxoacid Salt:
2 KClO3(s) → 2 KCl (s) + 3 O2(g)
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Oxygen Reactivity
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The reactivity of oxygen is based on its electron
configuration and its high electronegativity.
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Oxygen Reactivity
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Reactivity is based on electron configuration and
high electronegativity.
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Ionic Oxides:
4 Li(s) + O2(g) → 2 Li 2O(s)
2 Mg(s) + O2(g) → 2 MgO(s)
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Covalent Oxides:
2 H2(g) + O2(g) → 2 H2O(l)
C(s) + O2(g) → CO2(g)
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Oxygen Reactivity
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Oxygen reacts with
all elements except
noble gases and a
few metals.
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Reactions are slow
at room temperature,
but are rapid at high
temperatures.
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Oxides
01
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Oxides: Ionic character decreases across the
periodic table, from
left to right.
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Acidic character
increases from
left to right.
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Basicity increases
down a group.
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Oxides
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Slide 19
02
As bonding changes from ionic to covalent, the
structure changes from crystalline to molecular.
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Oxides
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Oxides
•
•
04
Basic oxides react with water to form hydroxides.
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Na 2O(s) + H2O(l) → 2 Na+(aq) + 2 OH–(aq)
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BaO(s) + H2O(l) → Ba 2+(aq) + 2 OH–(aq)
Acidic oxides react with water to form H+ ions.
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CO2(g) + 2 H2O(l) → H+(aq) + HCO3–(aq)
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N2O5(g) + H2O(l) → 2 H+(aq) + NO3–(aq)
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P 4O10(s) + H2O(l) → 4 H+(aq) + 4 H2PO4–(aq)
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Oxides
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Acidic Properties of Carbon Dioxide:
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06
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Amphoteric oxides exhibit both acidic and basic
properties. The classic example is Al2O3:
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Basic behavior:
Al2O3(s) + 6 H+(aq) → 2 Al3+(aq) + 3 H2 O(l)
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Acidic behavior:
Al2O3(s) + 2 OH–(aq) + 3 H2O(l) → 2 Al(OH) 4–(aq)
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Oxides
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Oxides, Peroxides, and Superoxides: Oxygen
forms three oxides, O2–, O22–, and O2–.
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The ions are all strong Brønsted bases:
Oxide: O2–(aq) + H2O(l) → 2 OH –(aq)
Peroxide: O22 –(aq) + 2 H2O(l) → O2 (g) + 4 OH –(aq)
Superoxide: 4 O2–( aq) + 2 H2O(l) → 3 O2(g) + 4 OH –( aq)
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08
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Peroxides: The most
common peroxide is H2O2.
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H2O 2 can disproportionate
to form H2O and O2.
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H2O 2 has many applications
as antiseptic, bleach, and
even rocket fuel.
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Slide 25
Slide 26
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H2O 2 is both an oxidizing and a reducing agent.
H2O 2 oxidizes Br – to Br 2 and reduces Mn 7+ to Mn 2 +.
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Oxides
•
10
Hydrogen peroxide auto
decomposes to water
and oxygen gas.
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Catalase, an enzyme
present in blood,
catalyzes this reaction.
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Metal Peroxides: The peroxide
ion is a basic anion.
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The peroxide ion reacts with
water to form OH–.
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Metal superoxides decompose
in water to produce O2 and OH–.
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Oxides
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12
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Ozone: A toxic, light blue gas, with a distinct smell.
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Ozone can be formed photo- or electrochemically
from oxygen.
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The ozone molecule has a bent structure with a
bond angle of 116.5°.
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The main use of ozone is in purification and
deodorizing. It is a powerful oxidizing agent.
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Oxides
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Water
Slide 31
01
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Water is the most important compound of hydrogen
and oxygen.
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Nearly 75% of Earth’s surface is covered in water
(estimated at 1.35 x 1018 m3).
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Nearly 66% of the adult human body, and 93% of
the human embryo, is water.
•
Water for home, agriculture, and industrial use is
usually obtained from lakes, rivers, or underground.
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Water
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Water
•
03
Water reacts with alkali metals and halogens.
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Water
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Slide 34
03
Water reacts with alkali metals and halogens.
2 Na(s) + 2 H2 O(l) → H2(g) + 2 Na +(aq) + 2 OH–(aq)
Ca(s) + 2 H2 O(l) → H2(g) + Ca 2+(aq) + 2 OH–(aq)
2 F2(g) + 2 H2O(l) → O2(g) + 4 HF(aq)
Cl2(g) + H2 O(l) æ HOCl(aq) + H+(aq) + Cl–(aq)
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Hydrates
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