Transcript AP Review - Eqn Writing

Equation Writing Review
Complexes and PPT’s
Acid-Base
Redox
Miscellaneous
AP Eq’n Writing Directions
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Write the formulas to show the reactants and the
products for the three laboratory situations described
below.
In all cases, a reaction occurs.
Assume that solutions are aqueous unless otherwise
indicated.
Represent substances in solution as ions if the
substances are extensively ionized.
• Strong acids and ionic compounds are extensively ionized
• Not dissolved means no ions!
Directions (continued)
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Omit formulas for any ions that are unchanged by
the reaction.
• Leave out spectators
• Words like solid, liquid, gas, suspension, powdered,
piece of, strip, etc… mean no spectators
• One point penalty per reaction for showing spectators
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You must balance the equation.
Grading Equation Writing
1 point for correct reactant formula(s)
 2 points for correct product formula(s)
 1 point for balancing
 1 point for answering simple related question
 -1 for including spectators
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There are often multiple acceptable product
predictions
Miscellaneous Equations - Organic
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Organic
• Combustion
Red flag is “burned”
 Form oxides (CO2, H2O, …)
 CS2 + O2 ---> CO2 + SO2 (or SO3)
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• Organic bases
Methylamine = CH3NH2 ---> CH3NH3+ = methylammonium
 Ethylamine = C2H5NH2
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• Dehydration synthesis: Can one lose H, the other OH?
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Review basic organic families and their structures
Misc. Equations - Synthesis
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Putting two pieces together
The only possibility in reactions between two elements
• P4 + O2 ---> P2O5
• Know strange allotropes?
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P4, S8, diatomics
• Criss-cross valences to get a reasonable product
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Good option for non-aq rxns of elem + cmpd
• NaS + O2 ---> NaSO3 (or similar)
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Occasionally for non-aq rxn of two compounds
• CaO + CO2 ---> CaCO3
Misc. Equations - Decomposition
When a single compound is heated, you must
break it up into smaller pieces
 These can be a bit dicey
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• make common products: water, CO2
• avoid elements (requires redox)
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Make 2 or 3 reasonable common products
• Frequently gases
• Carbonates ---> oxide + CO2
Criss-cross to get formula of oxide
 CaCO3 ---> CaO + CO2
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Review - Complex Eq’ns
Complex = Trans. Metal + Ligand
 Common complexing agents (aka, ligands)
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• NH3, OH-, SCN-, CN
Coordination number = # of ligands
• Twice the valence of the Trans Metal
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Be sure to carefully determine the correct charge
on the complex
Review - Precipitate Eq’ns
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Common precipitating agents
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Sulfide (S-2)
Hydroxide (OH-)
Carbonate (CO3-2)
Phosphate (PO4-3)
Silver, lead, mercury
Sulfate (SO4-2) with Ca, Ba, Sr
Know formulas and valences cold
 Criss-cross valences to get correct formula of PPT
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Review - Acid Base Eq’ns
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Look for obvious acid or base (don’t forget NH3)
Look at other reactant - is it a base or acid?
Proton transfer
Look for
• Conjugates of weak acids
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Fluoride, acetate, phosphate,
• Conjugates of weak bases
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Ammonium
• Oxides, which are anhydrides
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Metal oxides are bases, nonmetal oxides are acids
• Carbonates, which do the fizzy reaction with acids
Review - Redox Eq’ns
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Memorize Redox “nuggets”
• Permanganate, chromate, dichromate, nitric acid
• Also, sulfuric acid, halogen/halide, metal/metal ion,
two metal ions
Determine if the nugget is OX or RED
 Determine if other reactant can be RED or OX
 Add half-reactions and balance
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The Eq’n Writing Process
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Scan the list of eight, and as you do
• Cross out likely spectators
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But ONLY if in solution
Sodium, potassium, nitrate are spectators
Sulfate can be a spectator, but look out for a PPT
• Circle key words like solid, liquid, gas, suspension, powder,
piece of ….
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These indicate no spectators
• Underline red flags
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For Redox, AcidBase, PPT, Complex
• Label rxn as AB, Comp, PPT, Redox, etc…
Red Flags
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Complex formation
• Ammonia, hydroxide, thiocyanate, cyanide
• Other reactant must contain a trans. Metal
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PPT
• Sulfide, hydroxide, carbonate, phosphate, Ag/Pb/Hg
• Sulfate with barium/calcium
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Acid Base
• Acid, hydroxide, ammonia, oxide in water, carbonate
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Redox
• Permanganate, chromate, dichromate, nitric acid, peroxide