Predicting ReactionsGeneral Rules

1. All reactions occur

2. Net ionic reactions only

3. Phases are not required : aqueous by charge

4. Completely dissociated chemicals shown as ions (i.e. strong acid is H+ & A-)

5. All other dissociated chemicals shown as complete compound (i.e. weak acid is HA)

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Predicting ReactionsGeneral Rules (Pg 2)

6. “Burned in air” - means combustion in O2

7. “Heated” means decomposition

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Predicting ReactionsMajor Types

1. Look for two uncombined elements (Syn.)

2. Look for single reactant (Decomposition)

3. Look for Combustion Reaction

4. Look for Acid-Base Reactions (DR)

5. Look for Two Salt Solution (Precip)

6. Look for REDOX Reaction

7. Look for water as Reactant

8. Look for Transitional metal and Ligands

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Predicting Reactions

1. Looking for two uncombined elements (Syn)

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A. Must put them together. Need sensible oxidation #

B. Example : Solid sulfur is burned in oxygen

S + O2 => SO2

C. Example : A piece of solid zinc is heated in chlorine gasZn + Cl2 => ZnCl2

Predicting Reactions

2. Look for single reactant (Analysis)

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A. Only can break up into two or more product

B. Usually produces simple oxide and oxide gases

C. Example: Solid calcium carbonate is heated.CaCO3 => CaO + CO2

Predicting Reactions3. Look for Combustion Reactions

A. “Burned in air or oxygen is same

B. Always forms oxide gasesI. C - CO or CO2

II. H - H2OIII. S - SO2 or SO3

C. Example : Propane is burned in air

C3H8 + O2 => CO2 + H2O

D. Example : Carbon disulfide is burned in airCS2 + O2 => CO2 +

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SO2

Predicting Reaction

4. Looking for Acid-Base Reaction

A. Acid and Base

Be careful : only strong acid & strong basegive H+ + OH- => H2O

Weak acid/base : can’t get rid of other part

Example: Solution of hydrofluoric acid & sodium hydroxide are mixed

HF + OH- => F- + H2O (must keep F- )

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Predicting Reaction

4. Looking for Acid-Base Reaction (Cont’d)

B. Acid/Base with salt of other Remember : Hydrolysis (salts breaking up into ions)

Same as simple acid-base reaction

Example: Sol’n of hydrochloric acid & sodium bicarbonate is mixed

H+ + HCO31- => H2CO3

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Example : Sol’n of potassium hydroxide & ammonium chloride mix.

OH- + NH41+ => NH3 + H2O

Predicting Reaction4. Looking for Acid-Base Reaction (Cont’d)

C. Polyprotic acid & Sulfuric acid

Polyprotic : Only one H+ comes off or onException: “Excess acid”- goes all the way

Sulfuric acid - For now, assume both concentrated &dilute form completely dissociate

Example: “Equal volume” of “equimolar” solutions of phosphoric acid & potassium hydroxide are mixed

H3PO4 + OH1- => H2PO41- + H2O

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Example : Excess hydrochloric acid mixed w/sol’n potassium sulfide

H+ + S2- => H2S

Predicting Reaction5. Looking for Two Salt Solution

A. General Assumptions (Does not replace solubility rules)

I. A salt containing (1- charge) anion is SOLUBLE (don’t forget solubility rules especially AgCl)

II. A salt containing (2- or 3- charge) anion : INSOLUBLE (don’t forget solubility rules especially with sulfate)

Example: A sol’n of silver nitrate is added to potassium iodide sol’n

Ag+ + I1- => AgI (Remember reaction must occur)

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