AP CHEMISTRY NOTES 3-1 SYNTHESIS AND DECOMPOSITION REACTIONS

Transcription

1 AP CHEMISTRY NOTES 3-1 SYNTHESIS AND DECOMPOSITION REACTIONS SYNTHESIS REACTIONS Two or more elements or compounds combine to form a single product Know common oxidation states!!! A. Metals and nonmetals combine to form salts A piece of lithium metals is dropped into a container of nitrogen gas. B. Two compounds combine to form a single product (no water involved!!!). Sulfur dioxide gas is passed over solid calcium oxide. The gases boron trifluoride and ammonia are mixed. Carbon dioxide is passed over solid sodium oxide. DECOMPOSITION REACTIONS A compound breaks down into two or more elements or compounds. (Heat, electrolysis, or a catalyst are usually necessary.) A. A compound may break down to produce two elements. Sodium chloride is electrolyzed. B. Metallic carbonates break down to yield metallic oxides and CO2. Solid magnesium carbonate is heated.

2 C. Hydrogen peroxide breaks down to yield water and oxygen. A solution of hydrogen peroxide is decomposed catalytically. D. Ammonium carbonate (NH4)2CO3 breaks down to yield NH3, H2O, and CO2. A small quantity of ammonium carbonate is strongly heated. E. Sulfurous acid H2SO3 decomposes into SO2 and H2O. F. Carbonic acid H2CO3 decomposes into CO2 and H2O.

3 AP CHEMISTRY NOTES 3-2A BASIC NOMENCLATURE OF HYDROCARBONS AND ALCOHOLS Type of Compound Name Ending General Formula alkane -ane CnH2n+2 alkene -ene CnH2n alkyne -yne CnH2n-2 alcohol -anol or -yl alcohol CnH2n+1OH Alkane Alkene Alkyne Alcohol Nomenclature Prefix Number of Carbons Meth- 1 Eth- 2 Prop- 3 But- 4 Pent- 5 Hex- 6 Hept- 7 Oct- 8 Non- 9 Dec- 10 EXAMPLES: Propane Heptanol Butene Hexyne

4 AP CHEMISTRY NOTES 3-2B COMBUSTION REACTIONS COMBUSTION REACTIONS - Elements or compounds combine with oxygen 1. Addition of oxygen forms oxides of all substances in the fuel : carbon forms CO2 sulfur forms SO2 hydrogen forms H2O Carbon disulfide vapor is burned in excess oxygen. Silicon tetrahydride reacts in oxygen. 2. Hydrocarbons or alcohols combine with oxygen to form CO2 and H2O. Ethanol is burned completely in air.

5 AP CHEMISTRY NOTES 3-3 ANHYDRIDE REACTIONS ANHYDRIDE REACTIONS Water is involved as one of the reactants (the other reactant is an anhydride without water ) It is often advantageous to think of water as HOH in these reactions. A. Nonmetallic oxides (acidic anhydrides) + water yield acids. Carbon dioxide is bubbled through water. B. Metallic oxides (basic anhydrides) + water yield bases. Solid sodium oxide is added to water. C. Metallic hydrides + water yield metallic hydroxides and H2 gas. Solid sodium hydride is added to water. D. Highly active metals (Group IA and most of Group IIA) + water yield metallic hydroxides and H2 gas. Solid potassium is added to water. D. Amines (R-NH2) react with water to produce alkylammonium ions and hydroxide ions (these compounds act as dirty nasty hydrogen stealers just like NH3). Methylammine - CH3NH2 Ethylammine - C2H5NH2 Methylamine gas is bubbled into distilled water.

6 AP CHEMISTRY NOTES 3-4 SINGLE REPLACEMENT REACTIONS Single Replacement Reactions an element reacts with an ionic compound and replaces one of the elements in the compound Magnesium is added to a solution of iron(iii) chloride. Bromine and potassium iodide are mixed.. Reduction of a Metal Ore: Hot hydrogen gas is passed over copper(ii) oxide ore

7 AP CHEMISTRY NOTES 3-5 METATHESIS REACTIONS METATHESIS REACTIONS (DOUBLE REPLACEMENT) Two compounds react to form two new compounds with no change in oxidation number All double replacement reactions have a driving force that removes a pair of ions from solution: *formation of a precipitate *formation of a gas *formation of a molecular substance (ie. water in acid/base neutralization reactions) 1. Formation of a Precipitate *Know your solubility rules!!! Know the strong acids!!! *Split saturated solutions of any kind *Don t split solids, suspensions, or concentrated H2SO4 Solutions of silver nitrate and lithium bromide are mixed. Solid sodium carbonate reacts with a solution of calcium nitrate.

8 2. Formation of a Gas *Watch for the formation of a product that immediately reacts to form a gas The bell-ringers : H2CO3 NH4OH H2SO3 Excess hydrochloric acid solution is added to a solution of potassium sulfite. Crystals of ammonium chloride are added to a solution of sodium hydroxide. *Watch for equimolar volumes of acids added to polyvalent anions (ie. CO3 2-, PO4 3-, etc.) This adds only one hydrogen to the anion (so the resulting charge is not zero) Equimolar amounts of hydrochloric acid and solid barium carbonate are mixed. Excess hydrochloric acid and solid barium carbonate are mixed.

9 AP CHEMISTRY NOTES 3-6 ACID/BASE NEUTRALIZATION REACTIONS Formation of a Molecular Substance: *Watch for the formation of water Dilute solutions of lithium hydroxide and hydrobromic acid are mixed. Gaseous hydrofluoric acid is mixed with solid silicon dioxide. *Watch for ammonia and the related ammines (R-NH2) which act as dirty nasty hydrogen stealers in chemical reactions A solution of ammonia is reacted with dilute acetic acid. *Watch for equimolar solutions of bases (hydroxides) added to an acid This results in only one hydrogen being stolen by the base Equimolar solutions of potassium hydroxide and phosphoric acid are mixed

10 AP CHEMISTRY NOTES 3-7 REDOX REACTIONS REDOX REACTIONS Involve the gain and loss of electrons A. Look for common oxidizing / reducing agent pairs. Common Oxidizers Products Formed MnO4 - in acidic solution Mn 2+ Cr2O7 2- in acidic solution Cr 3+ HNO3 - concentrated NO2 (toxic!) HNO3 - dilute NO H2SO4 - hot, concentrated SO2 Metal-ic ions (ie. Fe 3+, Cu 2+ ) Metal-ous ions (ie. Fe 2+, Cu + ) Free halogens (ie. F2, Cl2, Br2, I2) Halide ions (ie. F -, Cl -, Br -, I - ) Common Reducers Halide ions Free Metals Metal-ous ions Products Formed Free halogens Metal-ous ions Metal-ic ions B. When an AP equation mentions an acidic or basic solution, it is probably redox. (Always add H + and H2O to reactions that are acidified.) A solution of tin(ii) chloride is added to an acidified solution of potassium permanganate. A solution of potassium iodide is added to an acidified solution of potassium dichromate. C. Copper / Nitric Acid Reactions: Copper is added to a concentrated solution of nitric acid. Copper is added to a dilute solution of nitric acid.

11 AP CHEMISTRY NOTES 3-8A NOMENCLATURE OF COMPLEX IONS COMPLEX IONS Complex ions (or coordination complexes ) contain coordinate covalent bonds bonds in which both electrons to be shared come from the same donor atom. The species that contain these donor atoms are called ligands. Ligands are usually neutral (ie. NH3) or negative (ie. NO3 - ). An ion that contains a metal cation sharing a coordinate covalent bond with one or more ligands is called a complex ion or coordination complex. (Notes: If a neutral species results from this bonding, it is called a coordination compound ). Ligands that have one donor atom are said to be monodentate. Ligands that contain more than one donor atom are said to polydentate. Complexes that consist of a metal atom (or ion) and polydentate ligands are said to be chelate complexes. The coordination number of a metal atom or ion in a complex is the number of donor atoms to which it is coordinated. The coordination sphere is the portion of the complex containing the metal and its ligands.

12 NAMING COMPLEX IONS Complex Cations: *Ligands are named in alphabetical order. *The numbers of monodentate ligands are indicated using common prefixes. (di, tri, tetra, penta, hexa, etc.) *The numbers of polydentate ligands are indicated using the following prefixes: bis 2 tris 3 tetrakis 4 pentakis 5 hexakis 6 *Polydentate ligand names are put in parentheses. (en)- ethylenediammine (edta) ethylenediamminetetraacetate (ox) or (C2O4 2- ) oxalate edta biting a metal *Negative ligand names end in o : S 2- (sulfido) CO3 2- (carbonato) SO4 2- (sulfato) NO3 - (nitrato) S2O3 2- (thiosulfato) *Neutral ligands often must be memorized. (See table on previous page for examples.) *The metal is written at the end of the coordination sphere, using a Roman numeral if the oxidation number is variable. No space is left between any portion of the coordination sphere. *Any portion outside of the coordination sphere is named as usual.

13 EXAMPLES: [Ag(NH3)2]Cl [Cr(OH2)6](NO3)3 [Ni(CO)4] [Co(en)2Br2]Cl [Cu(NH3)2(edta)2]Br2 [Co(en)4](NO3)3 [Co(NH3)4(OH2)Cl]Cl2 Bis(ethylenediammine)dinitritoiron(III) perchlorate Hexaphosphinealuminum sulfate

14 Complex Anions: *These are named just as the cations are, but the ending of the central atom (metal) name is changed to -ate: METAL aluminum antimony chromium cobalt copper gold iron lead manganese nickel palladium platinum silver tin zinc NAME OF METAL IN COMPLEX ANION aluminate antimonate chromate cobaltate cuprate aurate ferrate plumbate manganate nickelate palladate platinate argentate stannate zincate EXAMPLES: K2[Cu(CN)4] Na[Al(OH)4] Na2[Sn(OH)6] K4[Ni(CN)2(ox)2] Sodium difluorodinitritostannate(ii)

15 AP CHEMISTRY NOTES 3-8B COMPLEX REACTIONS COMPLEX REACTIONS Involve complex ions A. Common complex reactions in AP chemistry: Reactants Product Al + OH - [Al(OH)4] - or [Al(OH)6] 3- Al(OH)3 + OH - [Al(OH)4] - or [Al(OH)6] 3- Al 3+ + OH - [Al(OH)4] - or [Al(OH)6] 3- Ag + + NH3 [Ag(NH3)2] + Ag + + CN - [Ag(CN)2] - Zn(OH)2 + OH - [Zn(OH)4] 2- Zn 2+ + NH3 [Zn(NH3)4] 2+ Cu 2+ + NH3 [Cu(NH3)4] 2+ Cd 2+ + NH3 [Cd(NH3)4] 2+ Fe 3+ + SCN - [FeSCN] 2+ or [Fe(SCN)6 3- ] B. The number of ligands is usually twice the charge of the cation. Concentrated ammonia is added to a solution of copper(ii) nitrate. 6M sodium hydroxide is added to a solution of aluminum hydroxide. 5 drops of sodium thiocyanate are added to a solution of iron(iii) chloride.