Chemistry 102: Chapter 19: Electrochemistry

What is a voltaic cell?

It is a source of energy cause by a couple oxidation-redox reaction. It separates 2 reactions into two half-cells that allow for the flow of electrons through an external circuit.

true or false

Voltaic cell physically separates the two half reactions

true

Slide #12

what is monoatomic ion?

A monoatomic ion is an ion formed from a single atom that has gained or lost one or more electrons, resulting in a net charge.

Slide #12

Read

Oxidation Number For a monatomic ion, the actual charge of the atom or a hypothetical charge assigned to the atom in the substance using simple rules.

Slide #13

Fill in the blank

The oxidation number in an element is ___

The oxidation number of an atom in a monoatomic ion equals the ___ on the ion

The oxidation number of oxygen is __ in most compounds with the exception of peroxides where it is __.

The oxidation number of hydrogen is ___ in most compounds w/ the exception of binary compounds.

0
charge

-2,-1
+1

In relation to Slide #13

What is a binary compound?

A binary compound is a chemical substance made up of exactly two different elements, regardless of how many total atoms are present in the formula ex. HCl, NaCl, or CO.

Slide #14

What is halogens oxidation number? what is the exception to this rule?

The oxidation number of halogens is typically -1, but in compounds with oxygen or other elements more electronegative than themselves, it can be positive.

Slide #14

What is the oxidation # of a compound?

The sum of the oxidation numbers of the atoms in a compound is zero

Slide #14

What is the oxidation # of a polyatomic ion?

The oxidation number of a polyatomic ion is equal to the charge of the ion. For example, in the sulfate ion ($SO_4^{2-}$), the total oxidation number is -2.

Slide #15

Calculate the total and each oxidation numbers of each element in KMnO4?

In potassium permanganate (KMnO$_4$), the oxidation number of K is +1, Mn is +7, and each O is -2. The total oxidation number equals 0. (refer to the slide for help)

Slide #16

Calculate the total and each oxidation numbers of each element in K2MnO4?

In potassium manganate (K$<em>2$MnO$</em>4$), the oxidation number of K is +1, Mn is +6, and each O is -2. The total oxidation number equals 0. (refer to the slide for help)

Slide #17

What is the oxidation number of Cr in dichromate, Cr2O72-?

In dichromate ($Cr<em>2O</em>7^{2-}$), the oxidation number of Cr is +6. Each O is -2, and the total charge of the ion is -2. (refer to the slide for help)

Slide #18

What is a half reaction?

One of two parts of an oxidation–reduction reaction, one part of which involves a loss of electrons (or increase in oxidation number) and the other part of which involves a gain of electrons (or decrease in oxidation number)

Slide #19

What occurs during oxidation?

Oxidation involves the loss of electrons from a substance, resulting in an increase in its oxidation number. It often occurs simultaneously with reduction in a redox reaction.

Slide #19

What occurs during reduction?

Reduction involves the gain of electrons by a substance, resulting in a decrease in its oxidation number. It typically occurs alongside oxidation in a redox reaction.

Slide #20-27

Read

How to balance simple oxidation-reduction reactions

Steps

1. Assign oxidation numbers.

2. Identify oxidation and reduction by determining oxidation states.

3. Write unbalanced half-reactions.

4. Balance electrons in half-reactions.

5. Multiply half-reactions to equalize electrons.

6. Add half-reactions together.

7. Balance atoms and charges.

8. Combine the half-reactions to form the balanced equation

Slide #20-27

Balance the half-reaction equation for ZnAg

Refer to slides for step-by-steep instructions and answer

Slide #27

Balance the half-reaction equation for

The oxidation numbers are given below the reaction FeI3(aq) + Mg(s) → Fe(s) + MgI2(s)

Refer to slides for step-by-steep instructions and answer Slide #27-29

What is an electrochemicial cell?

An electrochemical cell is a device that converts chemical energy into electrical energy through redox reactions or vice versa. It consists of two electrodes (anode and cathode) and an electrolyte that allows the movement of ions.

Slides #30-

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Steps for electrochemical cell:

1. Our first step in studying electrochemical cell is to balance its oxidation–reduction reaction (First, we need to identify what is being oxidized and what is being reduced.)

2. Then, we determine if the reaction is in acidic or basic conditions.

3. Next, we construct the anode and cathode half-reactions. After that, we calculate the standard cell potential using the Nernst equation. Finally, we can analyze the overall cell reaction and its efficiency.

Slide #33

Read

How do we balance half reactions acid & basic step-by-step

Now we split the skeleton reaction into half-reactions and balance each half.

1. Balance all atoms except H and O.

2. Balance O atoms by adding H2O to the side of the equation that needs O.

3. Balance H by adding H+ to the side of the equation that needs H.

4. Balance the electric charge by adding electrons (e-) to the more positive side of the equation

Slide #33

How do we balance O in half-reactions?

Add H2O to the side needing O.

Slide #33

How do we balance H in half reactions?

Add H+ to the side needing H.

Slide #37

Dichromate ion in acidic solution is an oxidizing agent. When it reacts with zinc, the metal is oxidized to Zn2+, and dichromate ion is reduced. Assume that dichromate ion is reduced to Cr3+. -0 Write the balanced ionic equation for this reaction using the half-reaction method

Refer to slides for step-by-steep instructions and answer Slide #37-40