4.2 Standard potentials (Page 6/4)

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

I'm interested in biological psychology and cognitive psychology

Tanya Reply

what does preconceived mean

sammie Reply

physiological Psychology

Nwosu Reply

How can I develope my cognitive domain

Amanyire Reply

why is communication effective

Dakolo Reply

Communication is effective because it allows individuals to share ideas, thoughts, and information with others.

effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.

it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.

miss

Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment

Wekolamo Reply

please i need answer

Wekolamo

because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).

Manix Reply

Agreed 👍 There are many parts of our brains and behaviors, we really need to get to know. Blessings for everyone and happy Sunday!

ARC

A child is a member of community not society elucidate ?

JESSY Reply

Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?

Simon Reply

compare and contrast skinner's perspective on personality development on freud

namakula Reply

Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning

war

explain how nature and nurture affect the development and later the productivity of an individual.

Amesalu Reply

nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.

Samuel

I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills

Zyryn Reply

good👍

Jonathan

and having a good philosophy of the world is like a sandwich and a peanut butter 👍

Jonathan

generally amnesi how long yrs memory loss

Kelu Reply

interpersonal relationships

Abdulfatai Reply

What would be the best educational aid(s) for gifted kids/savants?

Heidi Reply

treat them normal, if they want help then give them. that will make everyone happy

Saurabh

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

	21 AP 21 Lymphatic Immune System MCQ By OpenStax Start Quiz
	4 Neuroanatomy 04 Spinal Cord Brain Stem By Stephen Voron Start Quiz
	Information Technology By Subramanian Divya Start Quiz
	Psychology By OpenStax Read Online Course
	3 Microbiology Final 3 By Madison Christian Start Test
	Macroeconomics By OpenStax Read Online Course
©flickr: Aaron	Computer Literacy Exam 1 By Lakeima Roberts Start Quiz
	2 BOD - Neuropathology By Brooke Delaney Start Exam
©flickr: Miguel	Protozoal and Parasitic Infections By Cath Yu Start Quiz
	Social Work midterm By Katy Pratt Start Exam