Quiz

1
Quiz
0. How many ways are commonly used for denoting a
molecule/ion?

• 1. Write the molecular formula of the following
  compounds

Sodium Chloride Calcium Phosphate Copper (II)
Chloride Nitric Oxide Hydrocyanic acid Potassium
Permagnate Sodium Borate Decahydrate
2. Write the name of the following compounds
CuSO4.5H2O
Na2ClO2
CuSO3
3. Write the meaning of the following prefixes
Mono-, Tetra-, Penta-, Hexa-, Octa-, Deca-
2
Answer
0. How many ways are commonly used for denoting a
molecule/ion? (1) Molecular structural
formula, (2) Ball-and-stick model, (3) Tube
structure, (4) Space-filling representation.

• 1. Write the molecular formula of the following
  compounds

Sodium Chloride NaCl Calcium Phosphate
Ca3(PO4)2 Copper (II) Chloride CuCl2 Nitric
Oxide HNO2 Hydrocyanic acid
HCN Potassium Permagnate KMnO4 Sodium Borate
Decahydrate NaBO3.10H2O
2. Write the name of the following compounds
CuSO4.5H2O
CuSO3
Na2ClO2
Copper (II) sulfate Sodium
chlorite Copper (II) sulfate pentahydrate
3. Write the meaning of the following prefixes
Mono-1, Tetra-4, Penta-5, Hexa-6, Octa-8,
Deca-10
3
Chapter 3 Chemical Reactions
The process that brings about a chemical change

• The carbon cycle is evident in fossils like this
  one, which are found in limestone, a form of
  calcium carbonate. The carbon atoms in limestone
  were once part of carbon dioxide molecules in the
  atmosphere. They were then taken up in the shells
  of marine organisms. When the organisms died, the
  shells settled to the bottom of the ocean and
  became compacted into limestone. Millions of
  years later, we dig up the limestone and use it
  to construct buildings. Some of the limestone is
  also heated to make quicklime in a process that
  releases the carbon atoms once again to the
  atmosphere as carbon dioxide.

4
Skeletal Equation
Reactants?Products
Substances formed in a chemical reaction
Staring materials
A reagent is a reactant only when it is being
used in a particular reaction.
sodiumwater?sodium hydroxidehydrogen
NaH2O?NaOHH2

• Skeletal equation

5
Chemical Equations
Law of Conservation of Mass Atoms are neither
created nor destroyed in a chemical reaction.
NaH2O?NaOHH2
2Na2H2O?2NaOHH2

• Balanced expression of chemical reactionchemical
  equation

Stoichiometric coefficients which give the molar
ratios of the reactants and products
Molecules
6
Reaction Conditions
States gas(g), liquid(l), aqueous(aq), solid(s)
2Na(s)2H2O(l)?2NaOH(aq)H2(g)
Temperature
CaCO3(s) CaO(s)CO2(g)
High temperature
Other conditions pressure, reaction time,
catalysts
7
Balancing Chemical Equations
H2O2?H2O
!
Danger!
H2O2?2H2O
Change the stoichiometric coefficients only!
2H2O2?2H2O
2H2(g)O2(g)?2H2O(l)
H2O2?H2O2
2HO?H2O
H21/2O2?H2O
8
Balancing A Chemical Reaction
C4H10O2?CO2H2O
C4H10O2?4CO25H2O
C4H10(13/2)O2?4CO25H2O
2C4H1013O2?8CO210H2O
2C4H10(g)13O2(g)?8CO2(g)10H2O(l)
!
9
Figure 3.6 When solutions of silver nitrate and
potassium chromate are mixed, a precipitate of
red silver chromate, Ag2CrO4, forms.
Precipitation reaction
Insoluble substance
potassium chromatesilver nitrate? Silver
chromatepotassium nitrate K2CrO4(aq)2AgNO3(aq)?A
g2CrO4(s)2KNO3(aq)
Soluble substance
10
Figure 3.7 These two beakers contain solutions
with different concentrations of the same solute.
The lighter color of the solution on the left (a)
shows that the solute is less concentrated than
in the solution on the right (b). In the
molecular-level view, we see that there are more
solute particles in a given volume of the more
concentrated solution.
solvent
Dissolve
Solutionsolventsolute
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Concentration

• The amount of solute molecules in a given volume
  of solution

12
Figure 3.8 Sodium chloride consists of sodium
ions and chloride ions. When it is added to water
(left), the ions separate and spread throughout
the solvent (right). The solution consists of
water molecules, sodium ions, and chloride ions.
There are no NaCl molecules present at any stage.
The overlays show only the solute.
Hydration of ions
Electrolyte a substance that dissolves to give a
solution that contains ions. Strong
electrolytes mostly ions. Weak electrolytes
mostly molecules Nonelectrolytes no ions
13
Nonelectrolyte
14
Nonelectrolyte
15
Figure 3.9 Pure water is a poor conductor of
electricity, as shown by the almost imperceptible
glow of the bulb in the circuit (a). However,
when ions are present, as in an electrolyte
solution, the solution does conduct. The ability
of the solution to conduct is low if it is a weak
electrolyte (b) but significant if it is a strong
electrolyte (c), even if the solute concentration
is the same in each case.
16
Figure 3.10 In a nonelectrolyte solution, the
solute remains as molecules and does not break up
into ions. Methanol, CH3OH, is a nonelectrolyte
and is present as molecules when it is dissolved
in water.
17
Figure 3.11 The formation of a silver chloride
precipitate occurs immediately as silver nitrate
solution is added to a solution of sodium
chloride.
Strong electrolyte
AgNO3(aq)NaCl(aq)?AgCl(s)NaNO3(aq)
18
Figure 3.12 A series of scenes in a solution of
sodium chloride. A sodium ion and a chloride ion
move together, linger near each other for a time
because of the attraction of their opposite
charges, and then move apart. The loose,
transient association of oppositely charged ions
is called an ion pair. The solution is shown both
with solvent molecules, for realism, and without,
for clarity.
19
Figure 3.13 In water, ions are hydrated that is,
they are surrounded by a cluster of water
molecules bound loosely to the ion. Note that a
hydrated cation (a) is surrounded by water
molecules oriented so that the O atom is closest
to the ion, whereas a hydrated anion (b) has
water molecules attached through their hydrogen
atoms. The number of hydrating molecules depends
on the size of the ion, but for most ions it is
approximately six.
Hydration of ions
20
Figure 3.14 In this precipitation reaction,
yellow lead(II) chromate is formed when lead(II)
nitrate solution is added to a solution of
potassium chromate.
Pb(NO3)2(aq)K2CrO4(aq)?PbCrO4(s)2KNO3(aq)
21
Quiz

• Explain the following concepts
• (1) Electrolyte (2) Hydration
• What is the real meaning of aq in a chemical
  equation?

22
Net Ionic Equations
AgNO3(aq)NaCl(aq)?AgCl(s)NaNO3(aq)
Complete ionic equation
Net ionic equation
spectator ions
23
Figure 3.15 Two depictions of a precipitation
reaction that results when the ions in two
electrolyte solutions are mixed (left beakers).
The top right beakers show the fate of all four
types of ions. By imagining the ionic reaction
without the spectator ions (bottom right
beakers), we can focus on the essential process
described by the net ionic equation.
24
Figure 3.16 How to write a net ionic equation.
Write the balanced overall equation (top), Then
show all ionic solutes as separate ions in the
complete ionic equation (second line), and delete
the spectator ions. The result is the net ionic
equation (bottom).
25
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26
Figure 3.17 Another example of a precipitation
reaction. This time, a solution of mercury(I)
nitrate is being added to a solution of potassium
iodide, and the insoluble product, mercury(I)
iodide, is precipitated. Notice that a yellow
color forms first. Mercury(I) iodide has two
solid forms. The yellow form precipitates first
but is soon converted to the more stable orange
form.
27
Figure 3.18 The shape of this shell is a result
of a precipitation reaction in which the
shellfish secreted calcium ions at certain points
on its surface. The calcium ions reacted with
carbonate ions in the surrounding water. The
colors of the shell are due to iron impurities
that were captured in the solid as it formed.
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The Reactions of Acids and Bases

• HCl (hydrochloric acid)
• CH3COOH (Acetic acid)
• NaOH (sodium hydroxide)
• NH4OH(ammonium hydroxide)

Arrhenius acid
Arrhenius base
29
HCl (hydrochloric acid)(Almost completely
ionized in aqueous solution)
Strong/Weak Acids
CH3COOH (Acetic acid) (incomplete ionized in
aqueous solution)
30
Strong/Weak Bases

• NaOH (sodium hydroxide) (Almost completely
  ionized in aqueous solution)

• NH4OH(ammonium hydroxide)(Incompletely ionized
  in aqueous solution)

31
The strong acids and bases in water

• HBr(aq), HCl(aq), HI(aq), HNO3(aq), HClO4(aq),
  HClO3(aq), H2SO4(aq)
• Group 1 hydroxides, Alkaline earth metal
  hydroxides

32
Neutralization

• BaseAcid ?Salt Water (Others)
• HCl(aq)NaOH(aq)?NaCl(aq)H2O(l)
• 2HNO3(aq)Mg(OH)2?Mg(NO3)2(aq)2H2O(l)

Neutralizationproton transfer
33
Gas-Formation Reactions
!!!

• 2NaCl(s)H2SO4(l)?Na2SO4(s)2HCl(g)
• FeS(s)2HCl(aq)?FeCl2(aq)H2S(g)
• CaCO3(s)H2SO4(aq)?CaSO4(s)H2CO3(aq)?H2OCO2(g)

The reaction of acids with salts is a proton
transfer reaction that may produce gas or a
compound that decomposes into a gas.
34
Redox Reactions

• 6CO2(g)6H2O(l)?C6H12O6(s)6O2(g)
• (photosynthesis reaction)
• CH4(g)2O2(g)?CO2(g)2H2O(l)
• (Natural gas reaction)
• 2Mg(s)O2(g)?2MgO(s)
• Mg(s)Cl2(g)?MgCl(s)Zn(s)2HCl(aq)?ZnCl2(aq)H
  2(g)

Anything in common?
35
Figure 3.26 An example of an oxidation reaction
magnesium burning brightly in air. Magnesium also
burns brightly in water and in carbon dioxide
consequently, magnesium fires are very difficult
to extinguish.
2Mg(s)O2(g)?2MgO(s)
Oxidized (reducing agent)
Reduced (Oxidizing agent)
36
Figure 3.27When bromine is poured on red
phosphorus, a vigorous reaction takes place. In
the reaction phosphorus is oxidized and bromine
is reduced.
P(s)5Br(s)?PBr5(s)
Oxidized (reducing agent)
Reduced (Oxidizing agent)
37
They Are All Redox Reactions

• 6CO2(g)6H2O(l)?C6H12O6(s)6O2(g)
• (photosynthesis reaction)
• CH4(g)2O2(g)?CO2(g)2H2O(l)
• (Natural gas reaction)
• 2Mg(s)O2(g)?2MgO(s)
• Mg(s)Cl2(g)?MgCl(s)Zn(s)2HCl(aq)?ZnCl2(aq)H
  2(g)

38
Figure 3.28 The common oxidation numbers of
main-group elements. Notice the tendency of
elements in the same group to assume the same
oxidation number.
How many electrons you want?
39
Figure 3.29 How to determine an oxidation
number. Each atom is imagined to be a separate
ion. Certain ions are assigned charges by using
the rules in Toolbox 3.3, and the charge on the
central atom is determined by considering the
overall charge on the species. (a) Oxide ions
in an oxoanion are given the charge of ?2
because there are four oxygen atoms and the
overall charge on the anion is -2, the charge on
the central atom must be 6. (b) This molecule
has three chlorine atoms with oxidation numbers
of -1, an oxygen atom (-2), and a hydrogen atom
(1). The sum of these oxidation numbers is -4
and the overall charge on the molecule is 0.
Thus, the central atom must have an oxidation
number of 4.
40
Determine Oxidation Number

• SO2
• X2(-2)0?x4
• x4(-2)-2?x6

41
Figure 3.30 When a strip of zinc is placed in a
solution that contains Cu2 ions, the blue
solution slowly becomes colorless and copper
metal is deposited on the zinc. In this redox
reaction, the zinc metal is reducing the Cu2
ions to copper and the Cu2 ions are oxidizing
the zinc metal to Zn2 ions. (a) The reaction.
(b) A visualization of the process.
42
Figure 3.31 (a) Copper reacts slowly with dilute
nitric acid to give blue Cu2 ions and the
colorless gas nitric oxide, NO. (b) When copper
reacts with concentrated nitric acid, nitrogen
dioxide, NO2, is produced instead of NO. The blue
solution is turned green by this brown gas.
43
Figure 3.32 Aluminum reacts vigorously with
hydrochloric acid to form soluble aluminum
chloride and water.
44
Case Study 3Astronauts on the space shuttle must
change the canisters of lithium hydroxide daily.
Here, Sidney Gutierrez carries out the task. Two
canisters are used, and one is changed every 12
hours so that the capacity to remove carbon
dioxide remains stable.
A Better Solution 4KO2(s)2CO2(g)?K2CO3(s)3O2(g)
CO2(g)2H2(g)?C(s)2H2O(l) 2H2O(l)?2H2(g)O2(g) (
Each element can be recovered and reused!)
CO2(g)2LiOH?Li2CO3(s)H2O(l)
45
Figure 3.33 The three main types of chemical
reactions discussed in this chapter can be
distinguished by the type of change taking place.
(a) In a precipitation reaction, ions mix and one
combination of ions is insoluble. (b) In a
neutralization reaction, hydrogen ions are
transferred from an acid to a base. (c) In a
redox reaction, electrons are transferred from a
reducing agent to an oxidizing agent.
46
Figure 3.34 We can predict the products of a
reaction by examining the reactants. (a) Two
soluble salts may form a precipitate. (b) An acid
and a hydroxide react to form a salt and water.
(c) When two elements react, a redox reaction
generally occurs. A metal and nonmetal react to
form an ionic compound and two nonmetals react to
form a molecular compound. (d) In combustion
reactions, organic compounds react with oxygen to
form carbon dioxide and water.
47
Three Most Important Types of Reactions

• Precipitation
• (Soluble salts exchange ions?ionic solids
• Proton transfer
• (Neutralization, Gas Formation)
• Electron transfer
• (Redox Reaction)

48
Assignment for Chapter 3

• 17,25,33,37,43,51,62