Post on 28-Dec-2015
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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