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L. S. Van Der Sluys Chapter 4 Reactions

Chapter 3 & 4: Reactions Part 2

Read: BLB 3.1–3.2; 4.2–4.4

HW: BLB 4:19, 24, 39, 49a, c, e, f, 51b, d

Supplemental Reactions 3–5

Know: • Exchange reactions (Metathesis) • Formation of a precipitate • Formation of a gas • Formation of a weak or non-electrolyte

(neutralization) Single Displacement Reactions

• Redox reactions • Oxidation numbers

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L. S. Van Der Sluys Page 2 Chapter 4 Reactions

Review Patterns of reactivity

• (Complete) Combustion reactions (Ch. 3.2)

C3H8(g) + 5O2 (g) ! 3CO2 (g) + 4H2O(g)

• Combination reactions (Chapter 3)

2Mg(s) + O2(!) ! 2MgO(s)

• Decomposition reactions (Chapter 3)

PbCO3(s) !PbO(s) + CO2(g)

• Exchange reactions (Chapter 4)

Precipitation Pb(NO3)2(aq) + 2KI(aq) ! PbI(s) " + 2KNO3(aq)

Neutralization

NaOH(aq) + HCl(aq) ! NaCl(aq) + H2O(!)

Gas formation 2HCl(aq) + Na2S(aq) ! H2S(g) # + 2NaCl(aq)

• Single displacement reactions (Redox: Ch. 4)

2Ca(s) + O2(g) ! 2CaO(s)


Exchange Reactions: GAS FORMATION 1. direct production of a gas (EX: H2, NO2, SO2) 2. formation of a weak acid which decomposes to a gas:

CO2 CO2 H2S N2

Example: Sodium Bicarbonate Plus HCl Molecular Equation

NaHCO3(aq)+HCl(aq) ! H2CO3(aq)+NaCl(aq) "

Ionic Equation

Na+(aq) + HCO3

$(aq) + H+(aq) + Cl$(aq) !

H2CO3 (aq)+ Na+(aq)+Cl$(aq)

"

Na+(aq) + Cl$(aq) + CO2(g)+ H2O(l)

Net Ionic Equation


Single Displacement reactions (Oxidation-Reduction)

Oxidation of Calcium metal by molecular O2

What is the Chemical Reaction??

!How do you know which species is being oxidized and which is being

reduced??


Rules for determining Oxidation States 1. Oxidation state of atom in elemental form is zero.

e.g. Cl2 O2 P4 C(s) S8

2. The oxidation number of a monatomic ion equals its

charge.

3. Some elements have “common” oxidation numbers that can be used as reference in determining the oxidation numbers of other atoms in the compound.

Alkali metals +1 Alkaline earth metals +2 Fluorine –1 Cl, Br, I almost always –1 O usually –2

peroxides (–1) & superoxides possible

H usually +1 Hydrides: metal-H compounds (–1)

4. Sum of oxidation numbers is equal to overall

charge of molecule or ion: • For a neutral compound the sum of oxidation

numbers equals zero. • For a polyatomic ion, the sum of the oxidation

numbers is equal to the charge on the ion.

5. Shared electrons are assigned to the more

electronegative atom of the pair: The more electronegative atom will have a negative oxidation number.


Oxidizing agents species that is actually being reduced

(gaining e–) in reaction

examples of good oxidizing agents: O2,

halogens, H2O2, HNO3, Cr2O7–, MnO4

–

Reducing agents species that is actually being oxidized

(losing e–) in reaction

examples of good reducing agents: H2,

C, metals


Oxidation-Reduction Reactions Zn(s) + CuSO4(aq) ! ZnSO4(aq) +Cu(s)

What is oxidized? What is reduced? What is the oxidizing agent?

What is the reducing agent?

Ionic equation: Net ionic equation


Examples of Oxidation Reduction Reactions

1. Acid + Metal

Mg(s) + 2HCl(aq) ! MgCl2 + H

2(g)

Ionic equation: Net ionic equation:

Spectator Ions:

2. Salt + Metal

Fe(s) + Ni(NO3)

2(aq) ! Fe(NO

3)

2 + Ni(s)

Ionic equation: Net ionic equation:

Spectator Ions:


Activity Series Predicts whether a certain metal will be

oxidized

Oxidation causes: • destruction of the metal framework • failure of machinery • deterioration (think rust) • weakening of metal


Using the Activity Series: Will the metal element displace the atom from its compound in a reaction?

Na(s) + H2O(l) !

Au(s) + H2O(g) !

Zn(s) + AgNO3(aq) !

Active metals (groups IA, IIA, Al)

Inactive (inert metals): jewelry metals

Other metals are in between.


Remember: An element that is higher in the activity series will displace an element below it. Zn(s) + CuSO4(aq) ! ZnSO4(aq)+ Cu(s)

Ag(s) + Cu(NO3)2(aq) ! NO REACTION

Demo: Al(s) + CuCl2(aq) ! AlCl3(aq)+ Cu(s)

Al(s) + HCl(aq) ! AlCl3(aq)+ H2(g)


Practice Questions: 1. What is the oxidation state of Cu in CuSO4? 2. What is the oxidation state of O in CuSO4? 3. What is the oxidation state of S in CuSO4?


Practice Question: What are the spectator ions for the reaction provided below? What is the net ionic reaction? 2HF + Ba(OH)2 ! 2H2O + BaF2

Practice Question: What are the spectator ions for the reaction provided below? What is the net ionic reaction?

NH3 + HCl ! NH4+ + Cl

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