Various Types of Reactions

Transcription

1 Various Types of Reactions Matthew Park Outline: 1. Synthesis / Replacement / Decomposition Reactions 2. Precipitation Reactions 3. Acid-Base Reactions 4. Summary: Metathesis Reactions NOTE: Not all of the following chemical reactions are balanced. They have been intentionally left unbalanced for your practice.

2 1. Synthesis reaction: occurs when two or more simple substances (elements or compounds) are combined to form one new and more complex substance. The general form of a synthesis reaction is element or compound + element or compound compound Fe + S FeS Single replacement (or simply displacement) reactions are a type of trivial redox reaction in which an element reacts with a compound. In that compound there must be an element similar in some way to the reacting element but less reactive. The similarity can be as fundamental as belonging to the same chemical family, or as loose as both having the same charge polarity in compounds. In any case, the more reactive element takes the place of the less active element in the compound and the less active element is "displaced": Cl2 + 2 KBr 2 KCl + Br2 Zn + CuSO4 ZnSO4 + Cu As a generalization, the metal with the more positive reduction potential will be replaced. It should not be forgotten that hydrogen may also be produced as the displaced element by active metals reacting with acids: Mg + 2 HCl MgCl2 + H2 This pattern is generally true for all dilute acids. In the case of VERY active metals like those of Groups I and II, hydrogen can be displaced from water (acids will also work, of course).

3 2. Single displacement reaction: occurs when one element displaces another in a compound. The general form of a single displacement reaction is element + compound element + compound Zn + 2HCl H2 + ZnCl2 3. Double displacement reaction: occurs when the cation (+) and the anion (-) of the two reactants are interchanged. The general form of a double displacement reaction is compound (AB) + compound (CD) compound (AD) + compound (CB) FeS +2HCl FeCl2 + H2S 4. Decomposition reaction: occurs when energy in the form of heat, light, electricity, or mechanical shock is supplied. A compound may decompose to form simpler compounds and/or elements. The general form of a decomposition reaction is compound two or more substances 5. Combustion Reactions: Combustion reactions can vary a good deal as soon as one steps out of the realm of hydrocarbons but the exam seldom indulges in other combustions unless they are simple combinations like the burning of a metal in air or oxygen. For the hydrocarbon combustions, the simple rule is that burning (combining with O2) produces carbon dioxide and water. This is true whether the hydrocarbon contains oxygen or not. However, if halogens or nitrogen are present, oxides of these elements may form as well. These are difficult to predict, although in the case of nitrogen, NO or NO2 would always be a reasonable guess. Some examples are found below: 2 C6H O2 12 CO H2O [fractions are not permitted] 4 Li + O2 2 Li2O Note that net-ionic versions of these reactions really don't exist since liquid water is generally not present.

4 NOTE - There are six general types of decomposition reactions: a. Some oxy-acids, when heated, decompose to form water and the nonmetal oxide. H2CO3 H2O + CO2 b. Some metallic hydroxides, when heated, decompose to form the metal oxide and water. Ca(OH)2 CaO + H2O c. Some metallic carbonates, when heated, decompose to form the metal oxide and carbon dioxide. Li2CO3 Li2O + CO2 d. Some metallic chlorates, when heated, decompose to form metal chloride and oxygen gas. 2KClO3 2KCl + 3O2 e. Most metallic oxides are stable, but a few decompose when heated to form the metal and oxygen gas. 2HgO 2Hg +O2 f. Some compounds can be decomposed by electricity into their elements. 2NaCl 2Na + Cl2

5 1 Precipitation RXN 1A. BroChoLi (Br, Cl, I are insoluble with Ag+¹, Pb+², Hg+¹) A solution of silver nitrate and lithium bromide are mixed: Ag+¹ + Br ¹ AgBr A solution of silver nitrate and sodium chloride are combined: Ag+¹ + Cl ¹ AgCl A solution of sodium iodide is added to a solution of lead (II) acetate: Pb+² + 2I ¹ PbI₂ A solution of sodium iodide and lead nitrate are mixed: Pb+² + 2I ¹ PbI₂ Equimolar solutions of lead (II) nitrate and magnesium iodide are combined: Pb+² + 2I ¹ PbI₂ Mercury (I) acetate solution is mixed with sodium iodide solution: (HgC₂H₃O₂ + NaI) 2Hg+¹ + 2I ¹ Hg₂I₂ 1B. LetMeSiCBS (SO₄ is insoluble with Ag+¹, Pb+², Hg+¹, Ca+², Ba+², Sr+²) A solution of lead (II) nitrate is added to a solution of potassium sulfate: Pb+² + SO₄ ² PbSO₄ Excess concentrated sulfuric acid is added to solid calcium phosphate: Ca₃(PO₄)₂ + 3H₂SO₄ 2H₃PO₄ + 3CaSO₄ NOTE: the entire chemical formula for calcium phosphate is written out because it is a solid and has no ionized form. NOTE: H₃PO₄ may not be written in its ionized form, because it has none. Solid lead (II) carbonate is added to a 0.5 M sulfuric acid solution: PbCO₃ + H+ + HSO₄ PbSO₄ + CO₂ + H₂O A solution of copper (II) sulfate is added to a solution of barium hydroxide: NOTE: this is a kind of Double Precipitation RXN. Ba+² + 2OH + Cu+² + SO₄² Cu(OH)₂ + BaSO₄ 1C. CrO₄ (CrO₄ is soluble with Group 1 elements, NH₄+, Ca+², Sr+²) A solution of silver nitrate and sodium chromate are mixed: 2Ag+¹ + CrO₄ ² Ag₂CrO₄ A solution of sodium chromate and lead nitrate are mixed: Pb+² + CrO₄ ² PbCrO₄ 1D. OH (OH soluble only with Group 1 elements, NH₄+, Ca+², Ba+², Sr+²) A solution of copper (II) sulfate is added to a solution of barium hydroxide: NOTE: this is a kind of Double Precipitation RXN. Ba+² + 2OH + Cu+² + SO₄² Cu(OH)₂ + BaSO₄

6 2 Acid-Base RXN / Neutralization Beginning: A solution of sodium hydroxide is added to a solution of ammonium chloride: A solution of ethanoic (acetic) acid is added to a solution of barium hydroxide: OH + NH₄+ NH₃ + H₂O HC₂H₃O₂ + OH ¹ H₂O + C₂H₃O₂ 2A. Weak Acid Formation Hydrogen chloride gas is bubbled through a solution of potassium cyanide: HCl + CN HCN + Cl NOTE: The entire chemical formula for HCl is written because it is a gas. (Gases cannot be ionized.) Excess concentrated sulfuric acid is added to solid calcium phosphate: H₂SO₄ + Ca₃(PO₄)₂ H₃PO₄ + CaSO₄ NOTE: Because there is an excess of concentrated sulfuric acid, the H₂SO₄ cannot form a hydration shell, thus not ionize-able. Dilute hydrochloric acid is added to a solution of potassium sulfite: A solution of ammonia is added to a dilute solution of acetic acid: H+ + SO₃² HSO₃ NH₃ + HC₂H₃O₂ NH₄+ + C₂H₃O₂ Solutions of ammonia and hydrofluoric acid are mixed: NH₃ + HF NH₄+ + F 2B. Weak Acid Formation - from a Non-metal Oxide (Acid Anhydride) and H₂O Excess hydrobromic acid solution is added to a solution of potassium hydrogen carbonate: Solid dinitrogen pentoxide is added to water: N₂O₅ + H₂O H+ + NO₃ H+ + HCO₃ H₂O + CO₂ (tired of making arrow signs...) e.g. Phosphorus (V) oxytrichloride is added to water: POCl₃ + H₂O H₃PO₄ + H+ + Cl 2C. Strong Acid Formation - from Non-metal Oxide (Acid Anhydride) and H₂O e.g. Solid dinitrogen pentoxide is added to water: N₂O₅ + H₂O HNO₃

7 2D. More Practice with the Concepts Enumerated Above 1. calcium metal is added to a dilute solution of hydrochloric acid --give at least one visual observation for this reaction 2. liquid bromine is added to a solution of potassium iodide --which substance is the oxidizing agent? 3. magnesium turnings are added to a solution of iron(iii) chloride --describe a color change that corresponds to the reaction you write 4. hydrogen gas is passed over hot iron(iii) oxide --which substance is reduced? 5. small chunks of solid sodium are added to water --describe a test to confirm the gaseous product in your reaction 6. hydrobromic acid is added to a solution of potassium hydrogen carbonate --when a gas produced by the reaction is bubbled through limewater, what visible change is expected? 7. aqueous potassium hydroxide is added to crystals of ammonium bromide --when moistened litmus paper is held over the reaction container, what change will be observed? 8. hydrogen chloride gas is bubbled through a solution of potassium cyanide --which species behaves as a Brønsted base?

8 Solutions: 1. Ca + 2 H + Ca 2+ + H2 --vigorous bubbling as hydrogen gas is produced 2. Br2 + 2 I - I2 + 2 Br - --bromine (Br2) is the oxidizing agent, accepting electrons from the iodide ions 3. 3 Mg + 2 Fe 3+ 3 Mg Fe (or Fe 2+ : Mg + 2 Fe 3+ Mg Fe 2+ ) --the yellow/orange color of the mixture turns dirty looking, eventually light green (Fe 2+ ) and perhaps to colorless (Fe + Mg 2+ ) 4. 3 H2 + Fe2O3 2 Fe + 3 H2O --the iron in the Fe2O3 is reduced to Fe 5. 2 Na + 2 H2O 2 Na OH - + H2 --if some of the gas is collected in a test tube of air and a lighted match brought to the mouth of the tube a popping noise will be heard 6. HCO3- + H + CO2 + H2O --limewater becomes cloudy when carbon dioxide contacts it due to the formation of CaCO3 7. NH4Br + OH - NH3 + Br - + H2O --the litmus paper will turn blue because ammonia gas is produced 8. HCl + CN - HCN + Cl - --the CN - ion behaves as a Brønsted base DON T GIVE UP YET! The info provided to you above maybe a whole bunch of confusing reactions BUT this final page will summarize general reactions that usually encompass any chemical reactions involving acids, bases, and salts.

9 3 Metathesis Reactions - reactions w/ two reactants, and ending with two products. 3A. Examples 1. dilute sulfuric acid is added to a solution of barium acetate --identify the spectator ions in this reaction; explain. 2. solutions of sodium phosphate and calcium chloride are mixed --what is the most likely color of the final reaction mixture?; explain 3. hydrogen sulfide gas is bubbled through a solution of silver nitrate --if a drop of the final reaction mixture is placed on litmus paper, what color will it turn? 4. manganese(ii) nitrate solution is mixed with sodium hydroxide solution --identify the spectator ions in this reaction; explain 5. 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? 6. sulfur trioxide gas is bubbled into a solution of sodium hydroxide --is the temperature of the mixture likely to increase or decrease? 7. dilute solutions of lithium hydroxide and hydrobromic acid are mixed --which of the reactant solutions will feel slippery on the skin? 8. 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?; explain 9. a solution of sulfuric acid is added to a solution of barium hydroxide --if equimolar amounts of the two reactants are mixed, what change will be indicated by a conductivity device?

10 (Answers on the next page) 1. H + + SO42- + Ba 2+ + CH3COO - BaSO4 + CH3COOH --since both products are poor electrolytes there are essentially no spectator ions 2. 3 Ca PO43- Ca3(PO4)2 --white; the absence of transition metals makes this likely 3. H2S + 2 Ag + 2 H + + Ag2S --red/pink since hydrogen ions are liberated in the reaction 4. Mn OH - Mn(OH)2 --sodium (Na + ) and nitrate ions (NO3-) 5. 3 Zn PO43- Zn3(PO4)2 --since sodium ions are spectators, they will be found in the solution and color the flame bright yellow 6. SO3 + 2 OH - SO42- + H2O --the temperature should increase as for any neutralization reaction 7. H + + OH - H2O --lithium hydroxide will feel slippery since it is a base 8. NH3 + CH3COOH NH4+ + CH3COO - --both reactants are weak electrolytes while the final mixture contains free ions so it should conduct much better 9. H+ + SO42- + Ba 2+ + OH - BaSO4 + H2O --if equal moles are mixed all of the ions will be combined in either a precipitate or water and thus the conductivity should be essentially zero