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8/7/2019 APChemNotes1

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Types of Chemical Reactions in Solutions

Just mixing two substances does not ensure that a reaction will happen. In a reaction, you must formnew substances (often a solid or gas) or transfer electrons.

1. Precipitation Reactions

If two solutions are mixed and a solid is formed that separates from the rest of the solution, it is

classified as a precipitation reaction. The substance must not be soluble in the solution to form aprecipitate. To predict if a precipitate is formed, solubility rules (page ______) can be consulted.

If you have an insoluble product, then a reaction has occurred! If the potential products are all

soluble, then you have not really had a reaction.

Predict the products (if any) of the following possible reactions and balance:

e.g., AgNO3 (aq) + CaBr2 (aq) ?

NaBr (aq) + BaSO4 (aq) ?

2. Acid/Base Reactions

(Just some brief notes now, more information later this year)

Electrolytes - substances that when dissolved in water conducts ________________

Acids

Contain H and produce ______ in an aqueous solution (Arrhenius Acid)

Strong Acids completely dissociate/ionize in water and thus are strong ________________

Memorize these Strong Acids!

HCl (aq) HClO4 (aq)HBr (aq) HClO3 (aq)

HI (aq) HNO3 (aq)

H2SO4 (aq)

Weak Acid


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Bases

Contain OH and produce __________ in an aqueous solution (Arrhenius Base)

Strong Bases - Completely dissociate/ionize in water and are thus strong _______________

Memorize these Strong Bases!

LiOH (aq) Ca(OH)2 (aq)NaOH (aq) Sr(OH)2 (aq)

KOH (aq) Ba(OH)2 (aq)

RbOH (aq)

CsOH (aq)

Weak Bases

Neutralization the reaction of an acid with a metal hydroxide base to produce salt and water

e.g.,

3. Oxidation-Reduction Reactions

Reduction gain or the apparent gain of an electron to lower the oxidation number

Reduction often seems like a misnomer! But, think of it as a reduction in ___________.

Oxidation lose or the apparent loss of an electron to increase the oxidation numberOxidation is another misnomer! No oxygen is needed for oxidation to happen.

Mnemonics anyone? How about OIL RIG or LEO says GER

Electrons are so desirable that they do not wander about; they are immediately picked-up by other

substances. So oxidation and reduction happen together. For this reason, these type of reactions arecalled __________ reactions.

To judge whether something is oxidized or reduced, it is necessary to know rules for assigningOxidation States (page ________ )

e.g., KClO3 (s) KCl (s) + KClO4 (s)


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The substance that causes oxidation is called the oxidizing agent. The oxidizing agent is always

___________.

The substance that causes reduction is called the reducing agent. The reducing agent is always

___________.

e.g., Identify the oxidizing agent and reducing agent in the following:

AgNO3 (aq) + Cu (s) Cu(NO3)2 (aq) + Ag(s)

4. Reactions in Solution

Formal Ionic EquationShows all chemicals involved in reaction whether they react or not! They just need to be present.

e.g., Na2SO4 (aq) + Pb(NO3)2 (aq) PbSO4 (s) + NaNO3 (aq)

This is an equation that involves the mixing of two ionic compounds that have been dissolved in water.

This can be drawn as:

Notice that the Formula Ionic Equation really does not accurately represent what is in the beakers.

Complete Ionic Equations

This type of equation shows all ions that are dissolved in water as individual particles instead ofcompounds. That is, if a dry ionic compound is dissolved in water, then the cation and anion are shown

as separate ionic compounds. Any compounds that are formed (new precipitates and gases) are shown

as well. So in a Complete Ionic Equation, if a substance is shown as a compound, it is in the beaker a

compound as well. It is sometimes difficult to know if a precipitate is formed or not. To determinethis, you must know the solubility rules (Table _____, page _____).

Re-write the equation above as a Complete Ionic Equation (be sure it is balanced)

Notice that some of the ions really have not undergone any change. These unchanged ions,

_____________ and _______________ . They are called spectator ions.


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Net Ionic Equations

Elimination of spectator ions from a Complete Ionic Equation results in a Net Ionic Equation. In this

type of equation, only those chemicals that have undergone change are represented. On the AP exam, itis important that you know how to write this type of equation.

From the example above, write the net ionic equation

e.g,

5. Balancing Redox Equations

This often cannot be done by simple inspection. The method we will learn is called the half-reactionmethod. To do this, a reaction will be broken down into two half reactions. These will be balanced and

then added back together to form the balanced redox reaction.

To balance an equation, both atoms of each kind and charge must balance. That is, the total charge of

the reactants must equal the total charge of the products. Keep both of these ideas in mind.

1. Write as much of the overall equation as possible without spectator ions

2. Create half reactions, one for oxidation and the other for reduction

3. Balance all elements in each half reaction. (For O and H, use H+, H2O and OH- as described inclass)

4. Balance the charge in each half reaction by adding electrons

5. Make the number of electrons equal in both half reactions by multiplying through by the

appropriate integer6. Add the two half reactions together and eliminate common terms. Notice that no electrons are

represented in the final equation

7. Check your answer. The charges and elements should both balance.

e.g., KMnO4 (aq) is mixed with FeSO4 (aq) in an acidic solution. This produces both Fe3+ and

Mn 2+ . Determine the balanced net ionic equation.

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