Transcript document

Writing AP Equations
Warm - Up
• Write the complete electronic configuration of the Fe
atom in the ground state. Would you expect the atom to
be paramagnetic or diamagnetic? (2000)
• Describe the energy change when an electron in a H atom
is promoted from n=1 to n=3. Explain the terms GROUND
state and EXCITED state in this context. (1999)
• Consider the element with atomic number 87. Write the
valence shell electron configuration of this element.
(2006)
• Give a possible set of quantum numbers for EACH
electron in the valence shell of the Aluminum atom in its
ground state. (1980)
Warm – Up Solutions
• Fe – ground state, para or diamagnetic?
element or metal ion?
1s2
2s22p6
3s23p6
4s23d6
Unpaired electrons = paramagnetic
Warm – Up Solutions
• Energy is absorbed and the electron is
promoted from its ground state (the lowest
energy state that the electron is normally
found) to an excited state (a state where
electrons are in higher energy states than
would otherwise normally be expected).
n = 1 (ground) to n = 3 (excited)
Warm – Up Solutions
• Atomic # 87
What is the principle
quantum # of valence shell?
What type of orbital?
7s1
Warm – Up Solutions
Where is Al?
What are the valence
electrons?
3s2 3p1
n=3
s subshell electrons = l = 0
p subshell electrons = l = 1
For l = 0, ml = 0
For l = 1, ml = -1,0,1
ms = ½ or - ½
Find addresses for EACH electron
3, 0, 0, ½ ; 3, 0, 0, - ½ ; 3, 1, -1, ½
Writing AP Equations
AP equation sets are found in the free-response
section of the AP test. You are given 3
equations. The equations are of mixed types.
The section is worth 15 points and is 15 % of the
free response grade. Free response is 55% of the
total AP test grade.
First classify the type of reaction.
Practice these!!! Speed and accuracy!
Types of Reactions
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1. Metathesis (double replacement)
2. Single replacement
3. Combustion
4. Acid/base neutralization
5. Combination
6. Decomposition
7. Reactions of anhydrides
8. Organic
9. Non-trivial redox
10. Complex ion formation or decomposition
11. Lewis acid/base (adduct formation)
Categories of Chemical Compounds
• Acids - 7 Strong acids: HCl, HBr, HI, HNO3, H2SO4,
HClO3, HClO4 to KNOW…all others dissolve but
only partially dissociate!!
• Bases – Strong bases: Group I and II hydroxides.
• Metal oxides -binary compounds of a metal and
oxygen (MgO, K2O)
• Non-metal oxides - binary compounds of a nonmetal and oxygen (NO, CO2)
• Salts (compounds of metals that are NEITHER
bases NOR oxides: see solubility rules!)
• Other (most compounds belong here!!!!!)
Soluble
Salts
(with
exceptions)
S
2-
NH4+
Nitrate
Acetate
Water
• Consider water as HOH (H+, OH-)
• Water is a good solvent because the
molecules are polar.
• The oxygen atoms have a partial negative
charge.
• The hydrogen atoms have a partial positive
charge.
• The angle is 105°
How Ionic solids dissolve
Click here for
Animation
H
H
H
H
H
Writing Net Ionic Equations
• All reactions will work, they never give you a
reactions that doesn’t proceed to products.
• Break up any IONIC compounds (salts, strong
acids, strong bases…)
• Covalent compounds, weak electrolytes, weak
acids and bases, solids, pure liquids, and gases
are NOT broken into ions!
• Suspensions are NOT broken into ions.
Metathesis (Double Replacement)
Two compounds react to form two new compounds.
No changes in oxidation numbers occur. All double
replacement reactions must have a "driving force"
that removes a pair of ions from solution.
HCl + NaOH → NaCl + HOH
AgNO3 + NaCl → AgCl + NaNO3
Metathesis Products
• Precipitate : insoluble substance formed by the
reaction of two aqueous substances. Two ions bond
together so strongly that water can not pull them
apart.
i.e. Solutions of silver nitrate and lithium bromide are
mixed
• Gas : Gases may form directly in a double replacement
reaction or can form from the decomposition of a
product such as H2CO3 or H2SO3.
i.e. Excess hydrochloric acid solution is added to a
solution of potassium sulfite
• Molecular substance: When a molecular substance
such as water or acetic acid is formed, ions are
removed from solution and the reaction "works".
i.e. Dilute solutions of lithium hydroxide and hydrobromic
acid are mixed
Practice Problems
Sodium hydroxide is mixed with phosphoric
acid.
Hydrogen sulfide is bubbled through a solution
of silver nitrate.
An excess of sodium hydroxide solution is added
to a solution of magnesium nitrate.
Dilute sulfuric acid is added to a solution of
barium acetate.
Single Replacement (displacement)
Reaction where one element displaces another in a
compound. One element is oxidized and another is
reduced. (Trivial redox)
A + BC  B + AC
The more easily oxidized metal replaces the less
easily oxidized metal. The metal with the most
negative reduction potential will be the most active.
Each halogen will displace less electronegative
(heavier) halogens from their binary salts (F
replaces Cl).
Remember there are no “no reactions”!!!
Most Active Metals on Top!
Reaction of Na+ and K+ with water…
Special Cases
• Non-aqueous: gas over hot metal oxides – no net
ionics…why?
• Weak acid/bases replaced by stronger acids/bases. What
indicates completion?
– NH4Cl + NaOH → NH3 + NaCl + H2O [molecular]
• Polyprotic acids i.e. H3PO4
– weak polyprotic acids will only reform step-by-step. The extent to
which the acid reforms depends on the amount of stronger acid
added.
• Equal volumes of equimolar solutions of sodium hydrogen
phosphate and hydrochloric acid are mixed : HPO42- + H+ →
H2PO4• Equal volumes of 0.10 M sodium hydrogen phosphate and
0.20 M hydrochloric acid are mixed : HPO42- + 2 H+ → H3PO4
– Notice that in the second case there is twice as much H+ available
so the reaction goes an additional step.
Practice Problems
Magnesium turnings are added to a solution of
iron(III) chloride
Chlorine gas is bubbled into a solution of
potassium iodide
Zinc metal is added to a solution of copper (II)
nitrate
Hydrogen gas is passed over hot copper(II) oxide
Single and Double Displacement Practice
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Manganese(II) nitrate solution is mixed with sodium hydroxide solution
– identify the spectator ions in this reaction; explain
• Solutions of zinc sulfate and sodium phosphate are mixed
– if a wire loop is dipped into the final reaction mixture and placed in a flame,
what color will the flame turn?
• Sulfur trioxide gas is bubbled into a solution of sodium hydroxide
– is the temperature of the mixture likely to increase or decrease?
• Dilute solutions of lithium hydroxide and hydrobromic acid are mixed
– which of the reactant solutions will feel slippery on the skin?
• A solution of ammonia is added to a dilute solution of acetic acid
– how does the conductivity of the final reaction mixture compare with that of
either reactant?
• Calcium metal is added to a dilute solution of hydrochloric acid
– give at least one visual observation for this reaction
• Liquid bromine is added to a solution of potassium iodide
– which substance is the oxidizing agent?
• Magnesium turnings are added to a solution of iron(III) chloride
– describe a color change that corresponds to the reaction you write
• Hydrogen gas is passed over hot iron(III) oxide
– which substance is reduced?
Combustion - Elements or compounds
combine with O2
• Hydrocarbons or alcohols combine with O2 to
form CO2 and H2O.
• Ammonia (NH3) combines with limited O2 to
produce NO and water IF excess O2 to produce
NO2 and H2O.
• Nonmetallic sulfides combine with oxygen to
form oxides and SO2.
If you add EXCESS oxygen, you make XO2 gases!
Try this! Solid Zn sulfide is heated in excess
oxygen
Combustion Practice
Carbon disulfide vapor is burned in excess O2.
Ethanol is burned completely in air.
Solid copper(II) sulfide is heated strongly in O2.
The hydrocarbon hexane is burned in excess O2
Anhydride Reactions
• Anhydride – without water. Water is a
reactant in these equations.
• Nonmetallic oxides (fake acid) plus water yield
acids
i.e. Carbon dioxide is bubbled into water
• Metallic oxides (fake base) plus water yield
bases
i.e. Solid sodium oxide is added to water
Anhydride Reactions
• Metal hydride + H2O  metal hydroxide + H2
• Phosphorous halides + H2O  hydrohalic acid
+ phosphorous containing acid.
• RNH3 – amine, organic base
CH3NH3 + H2O  OH- + RNH4+
Anhydride Practice
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Excess water is added to solid calcium hydride
Solid lithium hydride is added to water
Solid dinitrogen pentoxide is added to water
Phosphorus pentachloride solid is added to
water
• Solid potassium oxide is added to water
• Methylamine gas is bubbled into distilled
water
Addition/Combination Reactions
Two or more elements or compounds combine
to form a single product
• Group IA or IIA metal may combine with a
nonmetal to make a salt.
– A higher oxidation state of one nonmetal is
obtained when reacting with an excess of the other
nonmetal.
• Two nonmetals may combine to form a
molecular compound.
Addition Reactions
• A metallic oxide plus carbon dioxide yields a
metallic carbonate. (Carbon keeps the same
oxidation state)
• A metallic oxide plus sulfur dioxide yields a
metallic sulfite. (Sulfur keeps the same
oxidation state)
• A metallic oxide plus water yields a metallic
hydroxide.
• A nonmetallic oxide plus water yields an acid.
Addition Reaction Practice
• Solid calcium oxide is exposed to a stream of
carbon dioxide gas.
• Calcium metal is heated strongly in nitrogen
gas.
• A piece of lithium metal is dropped into a
container of nitrogen gas
• Sulfur dioxide gas is passed over solid calcium
oxide
Acid/Base Neutralizations
•Acids react with bases to produce salts and
water.
One mole of hydrogen ions react with one mole
of hydroxide ions to produce one mole of water.
Watch out for information about quantities of
each reactant! Remember which acids are
strong (ionize completely) and which are weak
(write as molecule).
Complex Ion Reactions
• Complex ion- the combination of a central
metal ion and its ligands
• Ligand- group bonded to a metal ion
• Coordination compound- a neutral
compound containing complex ions
[Co(NH3)6]Cl3 (NH3 is the ligand, [Co(NH3)6]3+is
the complex ion)
Complex ion
Name
Formed from:
• [Al(OH)4]- tetrahydroxoaluminate ion (Al or Al(OH)3 or
Al3++ OH-)
• [Ag(NH3)2]+ diamminesilver(I) ion
(Ag+ + NH3)
• [Zn(OH)4] 2- tetrahydroxozincate ion
(Zn(OH)2 + OH-)
• [Zn(NH3)4] 2+ tetramminezinc ion
(Zn2+ + NH3)
• [Cu(NH3)4]2+ tetramminecopper(II) ion (Cu2+ + NH3)
• [Cd(NH3)4] 2+ tetramminecadmium(II) ion (Cd2++ NH3)
• [FeSCN] 2+ thiocyanoiron(III) ion
(Fe3+ + SCN-)
• [Ag(CN)2]- dicyanoargentate(I) ion
(Ag+ and CN-)
Adding an acid to a complex ion will break it up. If HCl is added to a silver
Complex, AgCl(s) is formed.
If an acid is added to an ammonia complex, NH4+ is formed.
Types of Complex Ion
• Complexation of a soluble salt
• Complexation of an insoluble salt
• Destruction of a complex by acid/base
neutralization
Complex Ion Practice
• 1. Concentrated (15M) ammonia solution is
added in excess to a solution of copper(II)
nitrate.
• 2. An excess of nitric acid solution is added to
a solution of tetraaminecopper(II) sulfate.
• 3. Dilute hydrochloric acid is added to a
solution of diamminesilver(I) nitrate.
Oxidation Reduction Reactions
• Redox reactions involve the transfer of
electrons, and the oxidation numbers of at
least two elements must change.
• One charge goes up and the other goes down
• Polyatomics decompose to gases
• Go to metals first
• Never include Group I ion (unless it’s a solid)
or NO3- and unless it’s HNO3 metal
Stuff to Know
Common oxidizing agents
Products formed
MnO4- in acidic solution
Mn2+
MnO2 in acidic solution
Mn2+
MnO4- in neutral or basic solution
MnO2(s)
Cr2O72- in acidic solution
Cr3+
HNO3, concentrated
NO2
HNO3, dilute
NO
H2SO4, hot, concentrated
SO2
Redox Practice Problems
• A solution of tin(II) chloride is added to an
acidified solution of potassium permanganate.
• A solution of tin(II) sulfate is added to a
solution of iron(III) sulfate
• Hydrogen peroxide solution is added to a
solution of iron(II) sulfate
• A piece of iron is added to a solution of
iron(III) sulfate .