4.2 Standard potentials (Page 9/4)

Siyavula textbooks: grade 12 Page 1 / 4

Standard electrode potentials

The voltages recorded earlier when zinc and copper were connected to a standard hydrogen electrode are in fact the standard electrode potentials for these two metals. It is important to remember that these are not absolute values, but are potentials that have been measured relative to the potential of hydrogen if the standard hydrogen electrode is taken to be zero.

Conventions and voltage sign

By convention, the hydrogen electrode is written on the left hand side of the cell. The sign of the voltage tells you the sign of the metal electrode.

In the examples we used earlier, zinc's electrode potential is actually -0.76 and copper is +0.34. So, if a metal has a negative standard electrode potential, it means it forms ions easily. The more negative the value, the easier it is for that metal to form ions. If a metal has a positive standard electrode potential, it means it does not form ions easily. This will be explained in more detail below.

Luckily for us, we do not have to calculate the standard electrode potential for every metal. This has been done already and the results are recorded in a table of standard electrode potentials ( [link] ).

Standard Electrode Potentials

Half-Reaction	$E^{0} V$
$L i^{+} + e^{-} ⇌ L i$	-3.04
$K^{+} + e^{-} ⇌ K$	-2.92
$B a^{2 +} + 2 e^{-} ⇌ B a$	-2.90
$C a^{2 +} + 2 e^{-} ⇌ C a$	-2.87
$N a^{+} + e^{-} ⇌ N a$	-2.71
$M g^{2 +} + 2 e^{-} ⇌ M g$	-2.37
$M n^{2 +} + 2 e^{-} ⇌ M n$	-1.18
$2 H 2 O + 2 e^{-} ⇌ H_{2} (g) + 2 O H^{-}$	-0.83
$Z n^{2 +} + 2 e^{-} ⇌ Z n$	-0.76
$C r^{2 +} + 2 e^{-} ⇌ C r$	-0.74
$F e^{2 +} + 2 e^{-} ⇌ F e$	-0.44
$C r^{3 +} + 3 e^{-} ⇌ C r$	-0.41
$C d^{2 +} + 2 e^{-} ⇌ C d$	-0.40
$C o^{2 +} + 2 e^{-} ⇌ C o$	-0.28
$N i^{2 +} + 2 e^{-} ⇌ N i$	-0.25
$S n^{2 +} + 2 e^{-} ⇌ S n$	-0.14
$P b^{2 +} + 2 e^{-} ⇌ P b$	-0.13
$F e^{3 +} + 3 e^{-} ⇌ F e$	-0.04
$2 H^{+} + 2 e^{-} ⇌ H_{2} (g)$	0.00
$S + 2 H^{+} + 2 e^{-} ⇌ H_{2} S (g)$	0.14
$S n^{4 +} + 2 e^{-} ⇌ S n^{2 +}$	0.15
$C u^{2 +} + e^{-} ⇌ C u^{+}$	0.16
$S O_{4}^{2 +} + 4 H^{+} + 2 e^{-} ⇌ S O_{2} (g) + 2 H_{2} O$	0.17
$C u^{2 +} + 2 e^{-} ⇌ C u$	0.34
$2 H_{2} O + O_{2} + 4 e^{-} ⇌ 4 O H^{-}$	0.40
$C u^{+} + e^{-} ⇌ C u$	0.52
$I_{2} + 2 e^{-} ⇌ 2 I^{-}$	0.54
$O_{2} (g) + 2 H^{+} + 2 e^{-} ⇌ H_{2} O_{2}$	0.68
$F e^{3 +} + e^{-} ⇌ F e^{2 +}$	0.77
$N O_{3}^{-} + 2 H^{+} + e^{-} ⇌ N O_{2} (g) + H_{2} O$	0.78
$H g^{2 +} + 2 e^{-} ⇌ H g (l)$	0.78
$A g^{+} + e^{-} ⇌ A g$	0.80
$N O_{3}^{-} + 4 H^{+} + 3 e^{-} ⇌ N O (g) + 2 H_{2} O$	0.96
$B r_{2} + 2 e^{-} ⇌ 2 B r^{-}$	1.06
$O_{2} (g) + 4 H^{+} + 4 e^{-} ⇌ 2 H_{2} O$	1.23
$M n O_{2} + 4 H^{+} + 2 e^{-} ⇌ M n^{2 +} + 2 H_{2} O$	1.28
$C r_{2} O_{7}^{2 -} + 14 H^{+} + 6 e^{-} ⇌ 2 C r^{3 +} + 7 H_{2} O$	1.33
$C l_{2} + 2 e^{-} ⇌ 2 C l^{-}$	1.36
$A u^{3 +} + 3 e^{-} ⇌ A u$	1.50
$M n O_{4}^{-} + 8 H^{+} + 5 e^{-} ⇌ M n^{2 +} + 4 H_{2} O$	1.52
$C o^{3 +} + e^{-} ⇌ C o^{2 +}$	1.82
$F_{2} + 2 e^{-} ⇌ 2 F^{-}$	2.87

A few examples from the table are shown in [link] . These will be used to explain some of the trends in the table of electrode potentials.

A few examples from the table of standard electrode potentials

Half-Reaction	$E^{0} V$
$L i^{+} + e^{-} ⇌ L i$	-3.04
$Z n^{2 +} + 2 e^{-} ⇌ Z n$	-0.76
$F e^{3 +} + 3 e^{-} ⇌ F e$	-0.04
$2 H^{+} + 2 e^{-} ⇌ H_{2} (g)$	0.00
$C u^{2 +} + 2 e^{-} ⇌ C u$	0.34
$H g^{2 +} + 2 e^{-} ⇌ H g (l)$	0.78
$A g^{+} + e^{-} ⇌ A g$	0.80

Refer to [link] and notice the following trends:

Metals at the top of series (e.g. Li) have more negative values. This means they ionise easily, in other words, they release electrons easily. These metals are easily oxidised and are therefore good reducing agents .
Metal ions at the bottom of the table are good at picking up electrons. They are easily reduced and are therefore good oxidising agents .
The reducing ability (i.e. the ability to act as a reducing agent) of the metals in the table increases as you move up in the table.
The oxidising ability of metals increases as you move down in the table.

The following half-reactions take place in an electrochemical cell:

${Cu}^{2 +} + 2 e^{-} ⇌ Cu$

${Ag}^{-} + e^{-} ⇌ Ag$

Which of these reactions will be the oxidation half-reaction in the cell?
Which of these reactions will be the reduction half-reaction in the cell?

Determine the electrode potential for each metal
From the table of standard electrode potentials, the electrode potential for the copper half-reaction is +0.34 V. The electrode potential for the silver half-reaction is +0.80 V.
Use the electrode potential values to determine which metal is oxidised and which is reduced
Both values are positive, but silver has a higher positive electrode potential than copper. This means that silver does not form ions easily, in other words, silver is more likely to be reduced . Copper is more likely to be oxidised and to form ions more easily than silver. Copper is the oxidation half-reaction and silver is the reduction half-reaction.

Got questions? Get instant answers now!

Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?

Aislinn Reply

tijani

what is titration

John Reply

what is physics

Siyaka Reply

A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance

Jude Reply

Can you compute that for me. Ty

Jude

what is the dimension formula of energy?

David Reply

what is viscosity?

David

what is inorganic

emma Reply

what is chemistry

Youesf Reply

what is inorganic

emma

Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes

Adjei

please, I'm a physics student and I need help in physics

Adjanou

chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.

Pedro

A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity

Krampah Reply

2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.

Sahid Reply

you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s

Samuel Reply

can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?

Joseph Reply

Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time

Joseph

Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing

Joseph

"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true

Ryan

what's motion

Maurice Reply

what are the types of wave

Maurice

answer

Magreth

progressive wave

Magreth

hello friend how are you

Muhammad Reply

fine, how about you?

Mohammed

Mujahid

A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?

yasuo Reply

Who can show me the full solution in this problem?

Reofrir Reply

Got questions? Join the online conversation and get instant answers!

Jobilize.com Reply

<< Chapter < Page Page > Chapter >>

Read also:

Get Jobilize Job Search Mobile App in your pocket Now!

100% Free Mobile Applications
Receive real-time job alerts and never miss the right job again

Source: OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2

Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Siyavula textbooks: grade 12 physical science' conversation and receive update notifications?

Ask

	22 AP 22 Respiratory System MCQ By OpenStax Start Quiz
	Anthropology Biology Culture By Richley Crapo Start Assignment
©flickr: Luis	Chemistry Final Review By Madison Christian Start Exam
	1 AP 01 Human Body Anatomy Physiology Essay By OpenStax Start Flashcards
	12 AP 12 Nervous Tissue MCQ By OpenStax Start Quiz
	19 Sociology 19 Health and Medicine MCQ By OpenStax Start Quiz
	Social Psychology MCQ By Saylor Foundation Start Quiz
	20 Biology 20 Phylogenies the History of Life MCQ By OpenStax Start Quiz
	11 AP Key Terms 11 The Muscular System By OpenStax Start Key Terms
©flickr: Eduardo	Nursing Education NU589 Program Outcomes By Karen Gowdey Start Quiz