Exam #1 Review Sheet
CHEM 2124
Spring 2014
Electrochemistry
Definitions
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Oxidation – loss of electrons (OIL or LEO)
Reduction – gain of electrons (RIG or GER)
Oxidation/reduction reaction (Redox) – involves the transfer of electrons from one species to another
Oxidizing agent – what is being reduced (or causing oxidation) in a reaction
Reducing agent – what is being oxidized (or causing reduction) in a reaction
Basic Concepts
 Oxidation number of a species and rules for assigning oxidation numbers
 What are examples of Redox reactions?
o Combination, decomposition, displacement, combustion reactions
o General rule of thumb is that if the charges (oxidation numbers) change from left to right side or
reaction, then it is a Redox reaction
 Half reactions – Can you write outoxidation and reduction half reactions given a Redox reaction?
 Comparison of metals as effective reducing agents (like the first lab)
 Be familiar with the table of reduction potentials and how to use and interpret this table
o Strongest oxidizers are towards the top of the table, strongest reducers are towards the bottom
o Table lists REDUCTION potentials – oxidation reactions are written in the opposite direction
o To determine which is the anode and which is the cathode, look at the cell reduction table – the half-cell
which is closer to the top is more likely to be the anode and thus undergo oxidation
Electrochemical /Galvanic Cells
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Be sure you know how to draw a diagram of an electrochemical cell
Cathode – electrode where reduction occurs (RED CAT), Anode – electrode where oxidation occurs (AN OX)
Half cell – each of the compartments of an electrochemical cell
Cell diagram/cell notation - Anode is always on the left side of the double lines, cathode is always on the right
side of the double lines
 Electrons always flow from the anode to the cathode
 MEMORIZE:
E0cell = E0 red – E0 ox
Chemical Equilibrium
Equilibrium Concepts
 Chemical equilibrium is when the rate of the forward reaction equals the rate of the reverse reaction
 The equilibrium constant (Keq) is defined as [C]c[D]d/[A]a[B]b for the balanced reaction where
aA +bB
cC +dD
 When Keq > 1 the product side is favored and when Keq <1 the reactant side is favored
 Given concentrations at equliibirum, what is the calculated value of Keq?
 LeChatlier’s Principle says that a system will always shift to relieve the applied stress.
o What happens if the concentration of a chemical is increased? decreased?
o What happens when pressure is applied to a reaction with gases involved? – shifts to side with fewer
moles of gases
o What happens if a reaction is heated? If heat is removed? How is it different for an exothermic
reaction vs. an endothermic reaction?
Acid/Base Chemistry
Arrhenius Definition of Acids and Bases
 Acid produces H+ in water, Base produces OH- in water
Bronsted – Lowry Definition of Acids and Bases
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Acid – proton (H+) donor, transfers a proton to a base and is converted to its conjugate base
Base – proton (H+) acceptor, accepts a proton from an acid and is converted to its conjugate acid
Monoprotic, diprotic and triprotic acids – what are they? What is an amphiprotic (amphoteric) substance?
Relationship between strength of acid and strength of conjugate base
KNOW THE EXAMPLES OF STRONG ACIDS AND BASES provided in lecture, all others are weak
What is the difference between strong and weak in terms of ionization? – THIS IS KEY!!!
How can we use acid/base strength to determine the position of equilibrium in a reaction?
o Always favor reaction towards side of weaker acid and weaker base
Numeric Measures of Acid Strength (pH)
 What is Kw?
 MEMORIZE:
pH = -log [H3O+], pOH = -log [OH -]
 Solution is acidic if pH<7, neutral if pH = 7, basic if pH>7
 MEMORIZE:
pH + pOH = 14
 Strong acids are completely dissociated in water so, pH = -log (molar concentration of acid) for a strong acid
 MEMORIZE:
[H3O+] x [OH-] = 1 x 10 –14 = Kw (at 25°C)
Acid Ionization Constants (Ka and pKa)
 Definition of Ka and pKa
MEMORIZE: pKa = -log Ka
 Stronger acid has smaller pKa value and larger Ka value
 Acid is classified as weak if we list a pKa value for it and pKa is a positive number
Correlation between pH and pKa (or [H3O+] and Ka)
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MEMORIZE:
[H3O+] = √KaCo
Indicators
 What is an indicator?
 How can you estimate the pH value of a substance using a series of indicators? (Like you did in lab)
Common Acid Base Reactions
 What are the products of acids reacting with hydroxide bases? Of acids reacting with bicarbonate bases?
 Neutralization is acid+base  salt + water
Titrations
 How do you calculate the molarity of an acid or a base in a titration? How is the answer different if you have
a diprotic or triprotic acid? (MOLE RATIOS in the balanced equation!!!)
Titration Curves (Major Lab #1!)
 Used to graphically represent the pH throughout an acid/base reaction
o Two cases: Strong acid + Strong base and Weak acid + Strong base (How are they similar and how are
they different?)
 Understand the concepts in a titration curve and the differences between strong and weak as represented on
a pH curve
NOTE: YOU WILL NEED TO HAVE ALL FORMULAS IN RED TYPE MEMORIZED!!!!