# Reaction Predictions Rev 012312 Objectives SWBAT Review their

• Slides: 63

Reaction Predictions Rev. 01/23/12

Objectives SWBAT Review their knowledge of cations/anions, salts, diatomic molecules, strong acids and bases, solubility rules and the activity series. Review the proper format required to write molecular, and net ionic equations. Practice using Solubility Rules to determine if a reaction occurs.

New Format You will have a reaction prediction quiz every Wed. until the AP exam. The first quiz will be a group quiz (groups of 3) The next two quizzes will be pairs. The remaining quizzes will be individual.

The AP Way Always write net ionic equations. Balance the equations. There are 3 reaction prediction problems on the exam. There is an associated question with each reaction prediction question.

Most Commonly Used Cations and Anions Hydrogen H+ Sodium Na+ Potassium K+ Calcium Ca+² Magnesium Mg+² Iron (Ferrous) Fe+² Iron (Ferric) Fe+³ • Hydroxide OHˉ • Chloride Clˉ • Sulfide Sˉ² • Bicarbonate HCOзˉ • Carbonate COзˉ² • Sulfate SO 4ˉ² • Phosphate PO 4ˉ ³

Tip Group 1 A cations are spectator ions.

Cations/ Anions, contd. You can figure out the charge of an ion by using the periodic table. Ex: Alkali metals such as Lithium can easily lose an electron to become stable (just like a Noble gas) so taking away an electron give Lithium a +1 charge. On the other hand Halogens can easily accept an electron to become stable. Accepting an electron gives halogens a -1 charge.

Practice What is the oxidation state of Oxide? What is the oxidation state of Iodide? What is the oxidation state of a Calcium ion? What is the oxidation state of a Lithium ion?

Net Ionic Equation To create a net ionic equation, you break apart all ionic molecules in a balanced molecular equation into their ions if they are soluble. Do not break up gases or solids !!! Solids, pure liquids and gases have no charges. If there are spectator ions, ions that appear on both sides of the equation, they cancel each other.

Net Ionic Example Silver nitrate is mixed with potassium chromate Molecular Equation 2 Ag. NO 3 + K 2 Cr. O 4 → Ag 2 Cr. O 4 + 2 KNO 3 Complete ionic equation 2 Ag+ + 2 NO 3ˉ + 2 K+ + Cr. O 4 -2 → Ag 2 Cr. O 4 + 2 K+ + 2 NO 3 -2 Net Ionic Equation 2 Ag+ + Cr. O 4 -2 → Ag 2 Cr. O 4

Solubility Rules NO 3 - all nitrates are soluble CH COO or C 2 H 3 O 2 3 all acetates are soluble except Ag. CH 3 COO-1 Cl. O 3 - all chlorates are soluble Cl- all chlorides are soluble except Ag. Cl, Hg Cl , Pb. Cl 2 2 2 Br all bromides are soluble except Ag. Br, Pb. Br 2, Hg 2 Br 2, and Hg. Br 2 I all iodides are soluble except Ag. I, Hg I , Hg. I, and Pb. I 2 2 2

Solubility Rules, contd. SO 4 -2 all sulfates are soluble except Ba. SO 4, Pb. SO 4, Hg 2 SO 4, Ca. SO 4, Ag. SO 4 and Sr. SO 4 Alkali metal cations, and NH 4+1 are all soluble H+ all common inorganic acids and low molecular mass organic acids are soluble

(In)Solubility Rules, contd. CO 3 -² all carbonates are insoluble except those of alkali metals and NH 4 Cr. O 4 -² all chromates are insoluble except those of alkali metals, NH 4, Ca. Cr. O 4, and Sr. CO 4 OH all hydroxides are insoluble except those of the alkali metals, NH 4, Ba(OH)2, Sr(OH)2, and Ca(OH)2 PO 4 -³ all phosphates are insoluble except those of alkali metals and NH 4 SO 3 -² all sulfites are insoluble except those of alkali metals and NH 4 S-² all sulfides are insoluble except those of alkali metals and NH 4

Strong Acids HCl HNO 3 HBr H 2 SO 4 HI HCl. O 4

Strong Bases Generally, strong bases are made up of a metal ion and a hydroxide ion. Li. OH Ca(OH)2 Na. OH Sr(OH)2 KOH Ba(OH)2

Strong Acids and Bases Strong acids dissociate completely in water, so the reaction goes to completion and they never reach equilibrium with their conjugate bases. Because there is no equilibrium, there is no equilibrium constant, so there is no dissociation constant for strong acids and bases.

Salts are generally formed from a cation (on the far left side of the periodic table) and an anion (on the far right side of the table) Salts that are soluble in water include all of the salts of: Cations lithium sodium potassium ammonium Anions nitrate acetate Check the solubility rules for other soluble/insoluble salts

Diatomic Molecules You can use a mnemonic device to help you remember the diatomic molecules: Br. INCl. HOF (say “Brinkelhof”) Help Our Needy Class Find Brains Immediately

Synthesis occurs when two or more reactants combine to form a single product. There are several common types of synthesis reaction.

Synthesis Examples metal combines with a nonmetal to form a binary salt. A piece of lithium metal is dropped into a container of nitrogen gas. 6 Li+ N 2 2 Li 3 N Metal oxide and water forms a base (metallic hydroxide) Solid sodium oxide is added to water. Na 2 O + H 2 O 2 Na. OH

Synthesis, contd. Nonmetal oxide and water forms acids. Nonmetal retains its oxidation number. -Carbon dioxide is burned in water. CO 2 + H 2 O H 2 CO 3 Metallic oxide and nonmetallic oxide form salt. -Solid sodium oxide is added to carbon dioxide. Ca. O + SO 2 Ca. SO 3

Decomposition Occurs when a single reactant is broken down into two or more products. The reactants react to form basic compounds or elements. When a compound is heated or electrolyzed, it means that it is broken up into its ions. AB A+B

Decomposition Example Base metal oxide + water Ca(OH)2 Ca. O + HOH Acid containing oxygen non metal oxide + water H 2 CO 3 CO 2 + HOH Salt containing oxygen metal oxide + nonmetal oxide Ca. CO 3 Ca. O + CO 2

Examples of Decomposition A sample of magnesium carbonate is heated. Mg. CO 3 Mg. O + CO 2 Molten sodium chloride is electrolyzed. 2 Na. Cl 2 Na + Cl 2 A sample of ammonium carbonate is heated. (NH 4)2 CO 3 2 NH 3 + H 2 O + CO 2

Single Replacement Reactions that involve an element replacing one part of a compound. The products include the displace element and a new compound. An element can only replace another element that is less active than itself. (Look a activity series/ AP packet) Generally, synthesis reactions occur when the two reactants come from the following types of compounds: acid, base, salt, water A +BX B+AX

Single Replacement Active metals replace less active metals from the less active metals’ compounds in aqueous solutions 3 Mg+ 2 Fe. Cl 3 —> 2 Fe + 3 Mg. Cl 2 Active metals replace hydrogen in water 2 Na + 2 H 2 O —> H 2 + 2 Na. OH Active metals replace hydrogen in acids 2 Li + 2 HCl —> H 2 + 2 Li. Cl

Single Replacement Rules, contd. Active nonmetals replace less active nonmetals from their compounds in aqueous solutions Cl 2 + 2 KI —> I 2 + 2 KCl If a less reactive element is combined with a more reactive element in compound form, there will be no reaction Cl 2 + KF —> no reaction* * On the AP test reactions will ALWAYS have products; it will never be “no reaction. ”

Activity Series (Single Replacement) Metals Li, Ca, Na, Mg, Al, Zn, Fe, Pb, [H 2], Cu, Ag, Pt Nonmetals F 2, Cl 2, Br 2, I 2, More active Less Active

Double Replacement Two compounds react to form two new compounds. No changes in oxidation numbers occur. Each cation pairs up with the anion in the other compound. The “driving force” in these reactions is the removal of at least one pair of ions from solution. This removal of ions happens with the formation of a precipitate, gas, or molecular species. When a double replacement reaction doesn’t go to completion, it is a reversible reaction (no ions have been removed). AX+ BY AY+ BX

How do you know a double replacement reaction occurs? One of the products will be a(n): gas insoluble precipitate molecular species *Remember– on the AP test the reaction will always occur

Examples of Dbl. Replacement Solutions of potassium bromide and silver nitrate are mixed. KBr + Ag. NO 3 Ag. Br + KNO 3 A solution of sodium sulfate is added to a solution of hydrochloric acid. Na 2 SO 3 + 2 HCl 2 Na. Cl + H 2 SO 3 Remember that one of your products must be a solid or a gas.

Common Gases Released (Dbl. Repl. ) H 2 S Any sulfide plus any acid forms H 2 S and a salt. CO 2 Any carbonate plus any acid form CO 3, water, and a salt. SO 2 Any sulfite plus any acid form SO 2, water, and a salt. NH 3 Any ammonium plus a soluble hydroxide form NH 3, water, and a salt.

Solubility Computer Tasks Task #1 Go to the site listed below which is a tutorial on precipitation reactions. Follow all directions. Record the complete molecular reaction for each combination of solutions you mix. Identify the precipitate (name and formula) produced. http: www. wisconline. com/objects/index_tj. asp? obj. ID=GCH 2904

Solubility Computer Tasks Task # 2 Go to the site below and mix two solutions at a time. Write the complete molecular equations for each combination of solutions. Identify the precipitate (name and formula) that is produced. (You should have three reactions when you are finished. ) http: // www. mhhe. com/physsci/chemistry/animations/chang_7 e_es p/crm 3 s 2_3. swf

Acid/ Base Reactions (Dbl. Repl. ) An acid and a base will react and form water and a salt. Hydrochloric acid is added to sodium hydroxide. HCl + Na. OH Na. Cl + H 2 O

Acid/Base Reactions This is a neutralization reaction. Remember: Weak acids & bases do not dissociate in water Strong acids & bases do dissociate in water

Hydrolysis (Dbl. Repl. ) It is the reverse of neutralization and results when a salt plus a water molecule yields an acid plus a base. Salt + water acid + base Key things to know about hydrolysis reactions: Salts of a strong acid plus a weak base will hydrolyze into an acidic solution. NH 4+ +Cl- +H 2 O → H+ +Cl- + (NH)4 OH Salts of a weak acid and a strong base will always hydrolyze to give a basic solution. K+ +F- +H 2 O → K+ +OH- +HF

Hydrolysis Salts of a strong acid and a strong base will never undergo hydrolysis and therefore make a neutral solution. Na+ + Cl-1 + H 2 O → Na+1 + OH-1 + H+1 + Cl-1 Salts of a weak acid plus salts of a weak base may hydrolyze as an acid, base, or a neutral solution; the final result depends on the Ka’s and Kb’s of the acids and bases formed during the hydrolysis process. Disclaimer!! The spectator ions were not removed

Hydrolysis Sample Problems Try these: An aqueous solution of manganese (II) sulfate undergoes hydrolysis. Ammonium fluoride and water are mixed together. Answers are on the next slide.

Hydrolysis answers Mn. SO 4 + 2 H 2 O → H 2 SO 4 + Mn(OH)2 NH 4 F + H 2 O → HF + NH 4 OH

Gas Producing Reactions Acid + Metal carbonate → Salt + Water + Carbon dioxide H 2 SO 4(aq) + Mg. CO 3(s) → Mg. SO 4(aq) + H 2 O(l) + CO 2(g)

Combustion (Organic Rxns. ) An organic compound reacts with O 2 and an ignition source to form water and carbon dioxide. If something is burned there is a combustion reaction. Methanol is burned in oxygen gas. 2 CH 3 OH + 3 O 2 4 H 2 O + 2 CO 2

Combustion On the AP exam: If the reaction is a combustion reaction and you don’t know the chemical formula for the hydrocarbon, make up a chemical formula and complete the reaction. You will earn partial points.

Addition (Organic Rxns) A halogen, or hydrogen, is added to an alkene or alkyne, breaking apart the double or triple bonds and forming one compound with single bonds. This is an addition to multiple bonds. Fluorine is added to ethene F 2 + CH 2=CH 2 CH 2 F-CH 2 F

Substitution (Organic Rxns. ) An atom attached to a carbon is removed and something else takes its place. Classic reaction for organic cpds with no multiple bonds. This is a substitution of single bonds. Bromine is added to methane Br 2 + CH 4 CH 3 Br + HBr

Esterification (ether formation) An organic acid reacts with an alcohol to form an ester and water. organic acid + alcohol ester + water CH 3 CH 2 COOH + CH 3 CH 2 CH 2 OH CH 3 CH 2 COOCH 2 CH 2 CH 3 + H 20

Ether Formation alcohol + alcohol ether + water C 2 H 5 OH + C 2 H 5 OH C 2 H 5 OC 2 H 5 + H 2 O

Oxidizing Agents (Redox Rxns. ) Common Oxidizing Agents Mn. O 4¯ in acidic solution Mn. O 2 in acidic solution Mn. O 4¯ in neutral or basic solution Cr 2 O 7ˉ² in acidic solution HNO 3, concentrated HNO 3, dilute H 2 SO 4, hot, concentrated Metallic ions (higher oxidation #) Free halogens Na 2 O 2 HCl. O 4 C 2 O 4ˉ² H 2 O 2 Products Formed Mn +² Mn. O 2(s) Cr +³ NO 2 NO SO 2 Metallous ions (lower oxidation #) Halide ions Na. OH Clˉ CO 2

Handy Hint If the reaction prediction shows a chemical formula, such as, manganese (IV) oxide as a reactant, the reaction is probably an oxidation/reduction reaction.

Reduction Agents (Redox Rxns) Common Reducing Agents Halide ions Free metals Sulfite ions or SO Nitrite ions Free halogens, dilute basic 2 solution Free halogens, concentrated basic solution Metallous ions (lower oxidation #) Products Formed Free halogen Metal ions Sulfate ions Nitrate ions Hypohalite ions Halite ions Metallic ions (higher oxidation #)

Electrolysis (Redox Rxns) An electrolysis reaction is a reaction in which a non -spontaneous redox reaction is brought about by the passage of current under sufficient external electrical potential. The devices in which electrolysis reactions occur are called electrolytic cells. In theory, E° values (Standard Reduction Potentials) can be used to predict which element will plate out at a particular electrode when various solutions are combined. (B&L text)

Rules for Predicting Cathode Reactions (Reduction) When a direct electric current is passed through a water solution of an electrolyte, two possible reduction processes may occur at the cathode. The cation may be reduced to the corresponding metal. Mn+ + ne- M(s) (reaction 1) n = (charge of cation) Water molecule may be reduced to elementary hydrogen 2 H 2 O + 2 eˉ H 2 + 2 OHˉ (reaction 2)

Rules for Predicting Cathode Reactions, contd. For salts containing transition metal cations, which are relatively easy to reduced compared to water, reaction #1 will occur at the cathode (and the transition metal will plate out). Mn+ + ne- M(s) If the cation is representative metal, the water molecules will be easier to reduce compared to the cation, and reaction #2 will occur at the cathode, producing hydrogen gas and hydrogen ions. 2 H 2 O + 2 eˉ H 2 + 2 OHˉ

Rules for Predicting Anode Reaction (oxidation) The oxidation process that occurs at the anode of an electrolytic cell operating in aqueous solution may be one of two oxidation processes. The anion may be oxidized to the corresponding nonmetal. - 2 Xˉ X 2 + 2 eˉ (reaction 1) Water molecules may be oxidized to elementary oxygen. - HOH ½ O 2 + 2 H+ + 2 eˉ (reaction 2)

Rules for Predicting Anode Reactions, contd. For salts containing iodide, bromide, or chloride ions, it is usually easier to oxidize these nonmetals rather than water. It will be found that the nonmetal is formed at the anode. When the anion present is any other ion that is more difficult to oxidize than water, Reaction #2 will occur at the anode producing elementary oxygen and aqueous hydrogen ions.

Example Electrolysis Reactions 1. Copper (II) chloride in water Cu+2 + 2 Clˉ Cu + Cl 2 2. Copper (II) sulfate in water Cu+2 + HOH Cu + ½ O 2 + 2 H+ 3. Sodium chloride in water 2 Clˉ + 2 HOH H 2 + Cl 2 + 2 OHˉ 4. Sodium sulfate in water 2 HOH 2 H 2 + O 2

Metals w/ Multiple Oxidation Levels (Redox Rxns) These metals can change their oxidation state in a redox reaction Antimony (III) or (V) Bismuth (III) or (IV) Cerium (III) or (IV) Chromium (II) or (III) Cobalt (II) or (III) Copper (I) or (II) Gallium (I) or (III) Germanium (II) or (IV) Gold (I) or (III) Iron (II) or (III) Lead (II) or (IV) Mercury (I) or (II) Nickel (II) or (III) Thallium (I) or (III) Thorium (II) or (IV) Tin (II) sulfate is added to iron (III) sulfate Sn. SO 4 + Fe 2(SO 4)3 Sn(SO 4)2 + 2 Fe. SO 4

Complex Ion Reactions Nomenclature is on pages 23 -27 of The Ultimate Chemical Equations Handbook There a lot of very complicated types of these reactions, but, for all intensive purposes and for the AP test, you only need to be familiar with those reactions pertaining to ammonia and water. In a complex ion reaction, ligands will attach to a transition metal ion. There will usually be twice as many ligands as the metal’s oxidation number

Complex Ion Reactions, contd. These reactions usually occur in a concentrated solution of the ligand. Copper chloride (II) is added to a concentrated solution of ammonia Cu 2+ +NH 3 [Cu(NH 3)4]2+

Common Reaction Terms Electrolysis: Electricity is run through a compound, resulting in a change of oxidation states. Hydrolysis: The reaction of a salt with water to form molecular species. Salts of a strong acid + a weak base will always hydrolyze to give an acidic solution. Neutralization: Acid and base react to form a salt and water. Catalyst: A molecule that speeds a reaction but that does not appear in the reaction. Oxidation number: the charge that it would have if all the ligands (atoms that donate electrons) were removed along with the electron pairs that were shared with the central atom

Common Reaction Terms, contd. Precipitate: an insoluble substance formed by the reaction of two aqueous substances. Anode: the electrode where oxidation occurs an ox Cathode: the electrode where reduction occurs red cat

By: Will Lambert, Adam Robinson, Michelle Klassen, and Tori Waldron (AP Chem ‘ 06 -’ 07)