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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.

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Presentation on theme: "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."— Presentation transcript:

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2 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 2. Gas-Forming (includes flatulence)

3 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 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 + ---> Mg 2+ + 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? ok, lets start: Na + + CN - + Ag + + NO 3 - Ag(CN) 2 ¯ + Na + + NO 3 - Mn 2+ + SO NH S 2 - MnS + SO NH 4 + it sez solutions, so of course write ions for reactants! Yow! dont leave them like that! Rewrite them without spectators always: nonmetal oxide solid form (powder) P 2 O 5 (or: P 4 O 10 ) + H2OH2OH2OH2O H2OH2OH2OH2O 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! H 3 PO 4 Note: any complex ion of Ag+ with cyanide with consistent charge earns 3 pts; AgCN given as product earns 1 product pt. Mn 2+ + S 2 ¯ ---> MnS

5 (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 4 ) 2 CO 3 it sez solutions, so of course write ions for reactants! non-metal oxide H + + Cl - + KMnO 4 Note: HCl and MnO 4 ¯ acceptable as reactants. Any valid redox product earns one point. All four product earns two points. K + and/or H 2 O only as products earns no credit. If both H+ and H 2 O omitted, then maximum of two points possible. K + + Mn 2+ + Cl 2 + H 2 O recognize decomposition?! recognize decomposition?! Note: any one product earns one point; all three earn two points. NH 4 OH + CO 2 earns one product point. NH 3 + H 2 CO 3 eans one product point. (d) Solid ammonium carbonate is heated. NH 3 + H 2 O + CO 2 CO 2 + OH - HCO 3 - Note: CO 3 2 ¯ + H 2 O as products earns two product points. CO 3 2 ¯ alone as product earns one product point. HCO 3 ¯ + H 2 O earns one product point. Note: CO 3 2 ¯ + H 2 O as products earns two product points. CO 3 2 ¯ alone as product earns one product point. HCO 3 ¯ + H 2 O earns one product point. recognize KMnO 4 as a strong oxidizing agent! (Mn becomes __________) reduced)

6 (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 + H 2 O it sez solutions, so of course write ions for reactants! Note: HCl and MnO 4 ¯ acceptable as reactants. Any valid redox product earns one point. All four product earns two points. K + and/or H 2 O only as products earns no credit. If both H+ and H 2 O 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.. Na + + H 2 + OH - Fe 2+ + Cr 3+ + Note: All three products earn two product points. Any valid redox product earns one product point. H 2 O only earns no credit. If Cl¯ ---> Cl 2 instead of Fe > Fe 3+, then maximum of two points possible. Note: All three products earn two product points. Any valid redox product earns one product point. H 2 O only earns no credit. If Cl¯ ---> Cl 2 instead of Fe > Fe 3+, then maximum of two points possible. Cr 2 O H+H+H+H+ Fe 3+ + H2OH2OH2OH2O

7 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 + H2OH2OH2OH2O Ca(OH) 2 No penalty for the set of products { Ca 2+, OH –, and Ca(OH) 2 } No penalty for the set of products { Ca 2+, OH –, and Ca(OH) 2 } a-ha !! a metal oxide ! NH 4 NO 3 N 2 + OR: N 2 O + H 2 O a-ha !! decomposition! O 2 + H2OH2O 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)

8 . 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. Br 2 + I – > Br – + I 2 PbCO 3 + H + + HSO 4 – (or SO 4 2– ) > PbSO 4 + CO 2 + H 2 O (or HCO 3 – ) No reactant point earned for H 2 SO 4. No product point earned for H 2 CO 3 3. A mixture of powdered iron(III) oxide and powdered aluminum metal is heated strongly. Fe 2 O 3 + Al > Al 2 O 3 + Fe No penalty for the set of products { FeO, Fe, and Al 2 O 3 } 4. Methylamine gas is bubbled into distilled water. CH 3 NH 2 + H 2 O > CH 3 NH OH – CH 3 NH 2 + H 2 O > CH 3 NH OH – Two points earned for MeNH 2 + H 2 O > MeNH OH - Two points earned for MeNH 2 + H 2 O > MeNH OH - 5. Carbon dioxide gas is passed over hot, solid sodium oxide. 5. Carbon dioxide gas is passed over hot, solid sodium oxide. CO 2 + Na 2 O > Na 2 CO 3 6. A 0.2 M barium nitrate solution is added to an alkaline 0.2 M potassium chromate solution Ba 2+ + CrO 4 2– > BaCrO 4 (redox)

9 VIDescribing Reactions in Solutions zMolecular equation yGives the over all reaction AgNO 3 + NaCl AgCl (s) + NaNO 3(aq) zComplete ionic equation yShows reactants as ions and products as solid or ions Ag + (aq) + NO 3 - (aq) + Na + (aq) + Cl - (aq) AgCl (s) + Na + (aq) + NO 3 - (aq)

10 Hydrides, Carbides, and Nitrides Hydrides. Hydride anions are very strong bases. They react with proton sources to produce hydrogen (H 2 ). Ca 2+ + OH - + H2H2 KH + C 2 H 5 OH --> CaH 2 + H 2 O --> K + + C 2 H 5 O - + H 2

11 Li + N 2 --> Li 3 N Mg + N 2 --> Mg 3 N 2 Nitrides, nitrogen in a -3 oxidation state, are produced when nitrogen reacts with metals. Nitrides often hydrolyze to form ammonia. Mg 3 N 2 + H 2 O --> Mg(OH) 2 + NH 3 The hydrogens in acetylene (ethyne, C 2 H 2 ) are slightly acidic. Acetylides (carbides) hydrolyze to produce acetylene: Na 2 C 2 + H 2 O --> C2H2 C2H2 + Na + + OH - Calcium carbide, the most commonly encountered of these, was used in old (and dangerous) miner's lamps to produce acetylene.

12 Aqueous Oxidation-Reduction Aqueous 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): MnO HSO H + --> Mn 2+ + SO H 2 O Cr 2 O Sn 2+ + H + --> Sn 4+ + Cr 3+ + H 2 O

13 Hydrogen peroxide, H 2 O 2, behaves as a reducing agent with strong oxidizing agents: Cr 2 O H+ H+ + H 2 O 2 --> Cr 3+ + O 2 + H 2 O but as an oxidizing agent with reducing agents: Fe 2+ + H 2 O 2 + H + --> Fe 3+ + H 2 O Sometimes metals act as reducing agents: Pb + Ag + --> Ag + Pb 2+ and low valent metal ions as reducing agents: Sn 2+ + Fe 3+ --> Sn 4+ + Fe 2+

14 Commonly used oxidizing agents (cause oxidation, therefore are reduced) include: MnO 4 -, Cr 2 O 7 2-, O 2, and H2O2.H2O2. Commonly used reducing agents (cause reduction, therefore are oxidized) include: Fe 2+, Sn 2+, HSO 3 -, and also H2O2.H2O2.

15 Halogens Halogens are among the most commonly encountered elements in redox reactions because they support so many oxidation states. Fluorine, F 2, 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 I 3 - ).

16 Halides as reducing agents: I - + Fe 3+ --> Fe 2+ + I 2 MnO 2 + H + + Cl - --> Mn 2+ + Cl 2 + H 2 O H2O2 H2O2 + Br - + H + --> Br 2 + H2OH2O Halogens as oxidizing agents: Fe + Cl 2 --> FeCl 3

17 Halogens can disproportionate -- one atom goes to a higher oxidation value, while the other to a lower one: Cl 2 + OH - –> Cl - + OCl - + H 2 O 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: IO I- I- + H + ––> I 2 + H 2 O BrO Br - + H + –> Br 2 + H 2 O

18 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- I- + H+ H+ --> Cl - + I3- I3- + H2OH2O

19 Starch is added which forms an intensely blue colored complex with iodine (center). The iodine is titrated with sodium thiosulfate: I 3- + S 2 O 3 2- –> I - + S 4 O 6 2- Both I - and S 4 O 6 2- 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(S 2 O 3 ) 2 3- ].

20 Halogens also react with hydrocarbons to produce halocarbons: C 6 H 6 + Br 2 --> C 6 H 5 Br + HBr CH 4 + Cl 2 --> CCl 4 + HCl

21 lox zozone day while eating his lox and bagels,

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23 what are the reactants and what are the products? think, breathe, relax take your time just hurry up!

24 lox zozone day while eating his lox and bagels,

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26 what are the reactants and what are the products? think, breathe, relax take your time just hurry up!


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