A Common Theme for Reactions in Aqueous Solution Precipitation AgNO 3(aq) + KBr (aq) AgBr (s) + KNO 3(aq) Here the nitrate ions and bromide ions have exchanged places, and silver bromide pre-cipitates. Is this metathesis, too? Acid-Base In this reaction the nitrate and hydroxide ions have exchanged places, and water is one result. Acid-base reactions are also often referred to as proton- transfer reactions. That is, the H + ion transfers from the acid to the base, and water is the net result. In this gas-forming reaction the carbonate and sulfate ions have exchanged places, and H 2 CO 3 is one result. This latter compound decomposes to water and the gas CO . Gas-Forming (includes flatulence)
Here the nitrate ions and bromide ions have exchanged places, and silver bromide pre-cipitates. Is this metathesis, too?
Acid-Base
In this reaction the nitrate and hydroxide ions have exchanged places, and water is oneresult. Acid-base reactions are also often referred to as proton-transfer reactions. That is, the H+ ion transfers from the acid to the base, and water is the net result.
In this gas-forming reaction the carbonate and sulfate ions have exchanged places, andH2CO3 is one result. This latter compound decomposes to water and the gas CO2.
Gas-Forming(includes flatulence)
This table will be available on the AP Exam for the Predicting Reactants portion. Learn to use it well. It will come in handy for other parts of the exam, as well
This table will be available on the AP Exam for the Predicting Reactants portion. Learn to use it well. It will come in handy for other parts of the exam, as well
4) Give the formulas to show the reactants and the products for FIVE of the following chemical reactions. Each of the reactions occurs in aqueous solution unless otherwise indicated. Represent substances in solution as ions if the substance is extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. In all cases a reaction occurs. You need not balance.
Example: A strip of magnesium is added to a solution of silver nitrate.
Mg + Ag+ ---> Mg2+ + Ag
(a) Excess sodium cyanide is added to a solution of silver nitrate.
(When in doubt about the coordination number, double the absolute value of the charge on the positive ion.)
(b) Solutions of manganese(II) sulfate and ammonium sulfide are mixed.
(c) Phosphorous (V) oxide powder is sprinkled over distilled water.
Is this tricky? Well we have a in reacting with water… . ring a bell?
it sez “solutions”, so of course write ions for reactants!it sez “solutions”, so of course write ions for reactants!
Yow! don’t leave them like that! Rewrite them without spectators always:Yow! don’t leave them like that! Rewrite them without spectators always:
nonmetal oxide
nonmetal oxide
solid form (“powder”)solid form (“powder”)
PP22OO55 (or:(or: PP44OO1010) +) +PP22OO55
(or:(or: PP44OO1010) +) + HH22OOHH22OO
Note: Acidic species (H+ or oxyacid of phosphorous) earns one product point; P in +5 oxidation state in oxyanion earns one product point; anions of oxyacids of phosphorous require H+ for full credit for products.
Note: Acidic species (H+ or oxyacid of phosphorous) earns one product point; P in +5 oxidation state in oxyanion earns one product point; anions of oxyacids of phosphorous require H+ for full credit for products.
acid as product!acid as product!
HH33POPO44 HH33POPO44
Note: any complex ion of Ag+ with cyanide with consistent charge earns 3 pts; AgCN given as product earns 1 product pt.Note: any complex ion of Ag+ with cyanide with consistent charge earns 3 pts; AgCN given as product earns 1 product pt.
Mn2+ + S2¯ ---> MnS
(e) Carbon dioxide gas is bubbled through a concentrated solution of potassium hydroxide.
(f) A concentrated solution of hydrochloric acid is added to solid potassium permanganate.
(NH(NH44))22COCO33
it sez “solutions”, so of course write ions for reactants!
non-metal oxide
HH++ + Cl + Cl-- + + KMnOKMnO44
Note: HCl and MnO4¯ acceptable as reactants. Any valid redox product earns one point. All four product earns two points. K+ and/or H2O only as products earns no credit. If both H+ and H2O omitted, then maximum of two points possible.
K+ + Mn2+ + Cl2 + H2O
recognize decomposition?! recognize decomposition?! Note: any one product earns one point; all three earn two points. NH4OH + CO2 earns one product point. NH3 + H2CO3 eans one product point.
(d) Solid ammonium carbonate is heated.
NHNH3 3 + H+ H22O + COO + CO22
COCO2 2 + OH+ OH--HCOHCO33
-- Note: CO32¯ + H2O as products earns two product points. CO3
2¯ alone as product earns one product point. HCO3¯ + H2O earns one product point.
Note: CO32¯ + H2O as products earns two product points. CO3
2¯ alone as product earns one product point. HCO3¯ + H2O earns one product point.
recognize KMnO4 as a strong oxidizing agent! (Mn becomes __________)recognize KMnO4 as a strong oxidizing agent! (Mn becomes __________)reduced)reduced)
(h) A solution of potassium dichromate is added to an acidified solution of iron(II) chloride.
Calcium oxide powder is added to distilled water..
Na + HNa + H22OO
it sez “solutions”, so of course write ions for reactants!
Note: HCl and MnO4¯ acceptable as reactants. Any valid redox product earns one point. All four product earns two points. K+ and/or H2O only as products earns no credit. If both H+ and H2O omitted, then maximum of two points possible.
Note: all three products earn two product points. Any valid redox product earns one product point.
(g) A small piece of sodium metal is added to distilled water..
NaNa++ + H+ H22 + OH + OH--
FeFe2+ 2+ ++ CrCr3+ 3+ ++
Note: All three products earn two product points. Any valid redox product earns one product point. H2O only earns no credit. If Cl¯ ---> Cl2 instead of Fe2+ ---> Fe3+, then maximum of two points possible.
Note: All three products earn two product points. Any valid redox product earns one product point. H2O only earns no credit. If Cl¯ ---> Cl2 instead of Fe2+ ---> Fe3+, then maximum of two points possible.
CrCr22OO772- 2- ++ HH++ FeFe3+ 3+ ++ HH22OO
From 1999:
Students choose five of the eight reactions. Only the answers in the boxes are graded (unless clearly marked otherwise). Each correct answer earns 3 points, 1 point for reactants and 2 points for products. All products must be correct to earn both product points. Equations do not need to be balanced and phases need not be indicated. Any spectator ions on the reactant side nullify the 1 possible reactant point, but if they appear again on the product side, there is no product-point penalty. A fully molecular equation (when it should be ionic) earns a maximum of one point. Ion charges must be correct.
Calcium oxide powder is added to distilled water..
Solid ammonium nitrate is heated to temperatures above 300°C.
CaO +CaO + HH22OO Ca(OH)2
No penalty for the set of products { Ca2+, OH –, and Ca(OH)2 }No penalty for the set of products { Ca2+, OH –, and Ca(OH)2 }a-ha !! aa-ha !! a metal oxide !metal oxide !
Two points earned for NH4NO2 —> N2 + H2O No penalty for other oxides of nitrogen (e.g., NO, NO2, N2O3, N2O4 - but not N2O5)
Two points earned for NH4NO2 —> N2 + H2O No penalty for other oxides of nitrogen (e.g., NO, NO2, N2O3, N2O4 - but not N2O5)
.
1. Liquid bromine is shaken with a 0.5 M sodium iodide solution.1. Liquid bromine is shaken with a 0.5 M sodium iodide solution.
2. Solid lead(II) carbonate is added to a 0.5 M sulfuric acid solution.2. Solid lead(II) carbonate is added to a 0.5 M sulfuric acid solution.
Br2 + I – —> Br – + I2Br2 + I – —> Br – + I2
PbCO3 + H + + HSO4– (or SO4
2–) —> PbSO4 + CO2 + H2O (or HCO3– )PbCO3 + H + + HSO4
– (or SO42–) —> PbSO4 + CO2 + H2O (or HCO3
– )
No reactant point earned for H2SO4. No product point earned for H2CO3No reactant point earned for H2SO4. No product point earned for H2CO3
3. A mixture of powdered iron(III) oxide and powdered aluminum metal is heated strongly.3. A mixture of powdered iron(III) oxide and powdered aluminum metal is heated strongly.
Fe2O3 + Al —> Al2O3 + FeFe2O3 + Al —> Al2O3 + Fe No penalty for the set of products { FeO, Fe, and Al2O3 } No penalty for the set of products { FeO, Fe, and Al2O3 }
4. Methylamine gas is bubbled into distilled water.4. Methylamine gas is bubbled into distilled water.
5. Carbon dioxide gas is passed over hot, solid sodium oxide.5. Carbon dioxide gas is passed over hot, solid sodium oxide.
CO2 + Na2O —> Na2CO3CO2 + Na2O —> Na2CO3
6. A 0.2 M barium nitrate solution is added to an alkaline 0.2 M potassium chromate solution6. A 0.2 M barium nitrate solution is added to an alkaline 0.2 M potassium chromate solution
Ba2+ + CrO42– —> BaCrO4
Ba2+ + CrO42– —> BaCrO4
(redox)
VI Describing Reactions in Solutions
Molecular equation Gives the over all reaction AgNO3 + NaCl AgCl(s) + NaNO3(aq)
Complete ionic equation Shows reactants as ions and products
as solid or ionsAg+
(aq) + NO3-
(aq) + Na+ (aq)
+ Cl -(aq)
AgCl(s) + Na + (aq)
+ NO3-(aq)
Hydrides, Carbides, and Nitrides
Hydrides. Hydride anions are very strong bases.
They react with proton sources to produce hydrogen (H2).
Ca2+ + OH- + H2
KH + C2H5OH -->
CaH2 + H2O -->
K+ + C2H5O- + H2
Li + N2 --> Li3N
Mg + N2 --> Mg3N2
Nitrides, nitrogen in a -3 oxidation state,
are produced when nitrogen reacts with metals.
Nitrides often hydrolyze to form ammonia.
Mg3N2 + H2O --> Mg(OH)2 + NH3
The hydrogens in acetylene (ethyne, C2H2) are slightly acidic.
Acetylides (carbides) hydrolyze to produce acetylene:
Na2C2 + H2O --> C2H2 + Na+ + OH-
Calcium carbide, the most commonly encountered of these,
was used in old (and dangerous) miner's lamps to produce acetylene.
Aqueous Oxidation-ReductionAqueous oxidation-reduction reactions are among
the most consistently tested on the AP examination,
and these cover a vast range of reactivity patterns.
Common oxidizing agents (permanganate, dichromate):
MnO4- + HSO3
- + H+ --> Mn2+ + SO42- + H2O
Cr2O72- + Sn2+ + H+ --> Sn4+ + Cr3+ + H2O
Hydrogen peroxide, H2O2, behaves as a reducing agent
with strong oxidizing agents:
Cr2O72- + H+ + H2O2 --> Cr3+ + O2 + H2O
but as an oxidizing agent with reducing agents:
Fe2+ + H2O2 + H+ --> Fe3+ + H2O
Sometimes metals act as reducing agents:
Pb + Ag+ --> Ag + Pb2+
and low valent metal ions as reducing agents:
Sn2+ + Fe3+ --> Sn4+ + Fe2+
Commonly used oxidizing agents (cause
oxidation, therefore are reduced) include:
MnO4-, Cr2O7
2-, O2, and H2O2.
Commonly used reducing agents (cause
reduction, therefore are oxidized) include:
Fe2+, Sn2+, HSO3-, and also H2O2.
Halogens
Halogens are among the most commonly encountered elements
in redox reactions because they support so many oxidation states.
Fluorine, F2, is the strongest oxidizing agent.
Fluorine tends to form fluorides, or compounds
in which the oxidation number of the fluorine is -1.
The other halogens show oxidation states of
-1, 0, +1, +3, +5, and +7.
In addition, there are some special cases (such as -1/3 in I3-).
Halides as reducing agents:I- + Fe3+ --> Fe2+ + I2
MnO2 + H+ + Cl- --> Mn2+ + Cl2 + H2O
H2O2 + Br- + H+ --> Br2 + H2O
Halogens as oxidizing agents:
Fe + Cl2 --> FeCl3
Halogens can disproportionate -- one atom goes to a higher oxidation value, while the other to a lower one:
Cl2 + OH- –—> Cl- + OCl- + H2O
These reactions are reversible, and depend upon the acidity of the medium. In acid medium, the higher valent compounds react with halides to produce the halogens:
IO3- + I- + H+ ––> I2 + H2O
BrO3- + Br- + H+ –—> Br2 + H2O
An example of much of the chemistry is illustrated in the chemical analysis of bleach:Iodide is added to bleach and the mixture acidified (left):
OCl- + I- + H+ --> Cl- + I3- + H2O
Starch is added which forms an intensely blue colored complex with iodine (center).
The iodine is titrated with sodium thiosulfate:
I3- + S2O32- –—> I- + S4O6
2-
Both I- and S4O62- are colorless (right).
This last reaction of thiosulfate ion with an oxidizing agent to form tetrathionate ion is often encountered in iodine redox reactions. [Thiosulfate is better known as the fixer in photographic processes by forming Ag(S2O3)2
3-].
Halogens also react with
hydrocarbons to produce halocarbons:
C6H6 + Br2 --> C6H5Br + HBr
CH4 + Cl2 --> CCl4 + HCl
lox
one day while eating his lox and bagels,
lox
what are the reactants and what are the products?
think, breathe, relax
take your timetake your timejust hurry up!just hurry up!
lox
one day while eating his lox and bagels,
lox
what are the reactants and what are the products?
think, breathe, relax
take your timetake your timejust hurry up!just hurry up!
