Redox Chemistry and Electrochemical Cells

Comprehensive practice flashcards covering oxidation-reduction principles, oxidation number rules, balancing redox reactions, and electrochemical cell properties.

What is the definition of oxidation?

Loss of electrons.

What is the definition of reduction?

Gain of electrons.

What does the mnemonic 'OIL RIG' stand for?

Oxidation Is Loss, Reduction Is Gain.

What does the mnemonic 'LEO the lion says GER' stand for?

Loss of Electrons = Oxidation, Gain of Electrons = Reduction.

Identify the process when $Fe^{2+}$ becomes $Fe^{3+}.$

Oxidation.

Why is the transition from $Fe^{2+}$ to $Fe^{3+}$ considered oxidation?

Because it loses an electron.

Identify the process when $Cu^{2+}$ becomes $Cu^{+}.$

Reduction.

Why is the transition from $Cu^{2+}$ to $Cu+$ considered reduction?

Because it gains an electron.

What are redox reactions?

Reactions that involve both oxidation and reduction.

List common biological or chemical processes involving redox reactions mentioned in the text.

Combustion, corrosion, and cellular respiration.

What is a reducing agent?

A species that causes another species to be reduced.

What happens to the reducing agent during a redox reaction?

It gets oxidized.

Why does the reducing agent get oxidized?

It loses electrons.

What is an oxidizing agent?

A species that causes another species to be oxidized.

What happens to the oxidizing agent during a redox reaction?

It gets reduced.

Why does the oxidizing agent get reduced?

It gains electrons.

What is the quick DAT trick for identifying reduction and oxidation agents based on electrons?

Reducing agent = loses electrons; Oxidizing agent = gains electrons.

List four common oxidizing agents.

$O_2$, $O_3$, $H_2SO_4$, and Halogens.

Why are halogens considered strong oxidizing agents?

They want to gain electrons to complete their octet.

List four common reducing agents.

$H_2$, $Fe$, $Zn$, and Alkali metals.

Why are alkali metals considered strong reducing agents?

They want to lose one electron to reach a full octet.

Define oxidation number.

A number assigned to determine the degree of oxidation or reduction of an atom.

Why are oxidation numbers useful in chemistry?

They track electron transfer during reactions.

What do changes in an oxidation number represent?

Electrons gained or lost.

What is the oxidation number of an element in its elemental state?

0

What is the oxidation number of $Fe(s)$?

0

What is the oxidation number of $Li(s)$?

0

What is the oxidation number of $N_2(g)$?

0

What is the oxidation number of $Cl_2(g)$?

0

What is the oxidation number of $Ar(g)$?

0

What is the oxidation number of a monatomic ion?

Equal to the ion charge.

What is the oxidation number of $Na^+$?

$$+1$$

What is the oxidation number of $Mg^{2+}$?

$$+2$$

What is the oxidation number of $Fe^{3+}$?

$$+3$$

What is the oxidation number of Fluorine in compounds?

Always $-1$

What is the usual oxidation number of Oxygen?

$$-2$$

What is the usual oxidation number of Hydrogen?

$$+1$$

What is the oxidation number of Oxygen in peroxides such as $H_2O_2$?

$$-1$$

What is the oxidation number of Oxygen when bonded to Fluorine?

$$+1$$

What is the oxidation number of Hydrogen in metal hydrides?

$$-1$$

Provide an example of a metal hydride mentioned in the notes.

$$MgH_2$$

What is the oxidation number for Alkali metals (Group 1) in compounds?

$$+1$$

What is the oxidation number for Alkaline earth metals (Group 2) in compounds?

$$+2$$

What is the sum of oxidation numbers in a neutral molecule?

0

What is the sum of oxidation numbers in a polyatomic ion?

It equals the ion charge.

If an oxidation number increases, has oxidation or reduction occurred?

Oxidation.

If an oxidation number decreases, has oxidation or reduction occurred?

Reduction.

Which redox process specifically involves electron loss?

Oxidation.

Which redox process specifically involves electron gain?

Reduction.

Define a half-reaction.

The oxidation or reduction portion of a redox reaction.

What is the purpose of using half-reactions?

To visualize electron transfer.

In an oxidation half-reaction, where are the electrons shown?

As products.

In a reduction half-reaction, where are the electrons shown?

As reactants.

What is Step 1 in balancing a redox reaction in acidic conditions?

Separate the reaction into half-reactions.

What is Step 2 in balancing a redox reaction in acidic conditions?

Balance all atoms except $H$ and $O$.

What is Step 3 in balancing a redox reaction in acidic conditions?

Balance $O$ using $H_2O$.

What is Step 4 in balancing a redox reaction in acidic conditions?

Balance $H$ using $H^+$.

What is Step 5 in balancing a redox reaction in acidic conditions?

Balance charge using electrons.

What is Step 6 in balancing a redox reaction in acidic conditions?

Equalize electrons between the half-reactions.

What is Step 7 in balancing a redox reaction in acidic conditions?

Add the half-reactions and cancel common species.

Are the first four steps of balancing basic redox reactions identical to acidic ones?

Yes.

In basic conditions, what extra step occurs after adding $H^+$?

Add $OH^-$ to both sides.

Why is $OH^-$ added during basic balancing?

To neutralize the $H^+$.

What is formed when $H^+$ and $OH^-$ combine during balancing?

$$H_2O$$

In basic balancing, what is the final sequence after converting $H^+$ to $H_2O$?

Balance charges with electrons, equalize electrons, and add reactions.

Define an electrochemical cell.

A device that converts chemical and electrical energy through redox reactions.

In which part of an electrochemical cell does oxidation occur?

The Anode.

In which part of an electrochemical cell does reduction occur?

The Cathode.

What is the direction of electron flow in an electrochemical cell?

Anode to Cathode.

Does the direction of electron flow ever change between cell types?

No.

State the 'AN OX' part of the memory trick.

Anode = Oxidation.

State the 'RED CAT' part of the memory trick.

Reduction = Cathode.

Are galvanic (voltaic) cells spontaneous or nonspontaneous?

Spontaneous.

What is the sign of $\Delta G$ for galvanic cells?

Negative.

What is the sign of $E_{cell}^\circ$ for galvanic cells?

Positive.

Is an external power source required for a galvanic cell?

No.

What is the energy conversion in a galvanic cell?

Chemical to Electrical.

Describe the electron flow in terms of terminal charges for a galvanic cell.

Anode (-) to Cathode (+).

What is the charge of the anode in a galvanic cell?

Negative.

What is the charge of the cathode in a galvanic cell?

Positive.

Provide a common example of a galvanic cell.

A battery.

What is the purpose of a salt bridge?

To maintain electrical neutrality.

Name two typical electrolytes used in a salt bridge.

$NaNO_3$ and $KNO_3$.

Are salt bridge electrolytes reactive with the cell solutions?

No.

Toward which electrode do salt bridge anions move?

The Anode.

Toward which electrode do salt bridge cations move?

The Cathode.

What happens to the physical mass of a zinc electrode in a galvanic cell?

It shrinks.

Why does the zinc electrode shrink in a galvanic cell?

$Zn$ oxidizes into $Zn^{2+}.$

What happens to the physical mass of a copper electrode in a galvanic cell?

It grows.

Why does the copper electrode grow in a galvanic cell?

$Cu^{2+}$ plates onto the electrode.

Are electrolytic cells spontaneous or nonspontaneous?

Nonspontaneous.

What is the sign of $\Delta G$ for electrolytic cells?

Positive.

What is the sign of $E_{cell}^\circ$ for electrolytic cells?

Negative.

Is an external power source needed for an electrolytic cell?

Yes.

What is the energy conversion in an electrolytic cell?

Electrical to Chemical.

What is the direction of electron flow in an electrolytic cell?

Anode to Cathode.

What is the charge of the anode in an electrolytic cell?

Positive.

What is the charge of the cathode in an electrolytic cell?

Negative.

Does oxidation occur at the anode or cathode in an electrolytic cell?

Anode.

Does reduction occur at the anode or cathode in an electrolytic cell?

Cathode.