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The potent reducing power of hot magnesium is useful in preparing some metals from their oxides. Indeed, magnesium’s affinity for oxygen is so great that burning magnesium reacts with carbon dioxide, producing elemental carbon:

2Mg ( s ) + CO 2 ( g ) 2MgO ( s ) + C ( s )

For this reason, a CO 2 fire extinguisher will not extinguish a magnesium fire. Additionally, the brilliant white light emitted by burning magnesium makes it useful in flares and fireworks.

Group 12

The elements in group 12 are transition elements; however, the last electron added is not a d electron, but an s electron. Since the last electron added is an s electron, these elements qualify as representative metals, or post-transition metals. The group 12 elements behave more like the alkaline earth metals than transition metals. Group 12 contains the four elements zinc, cadmium, mercury, and copernicium. Each of these elements has two electrons in its outer shell ( ns 2 ). When atoms of these metals form cations with a charge of 2+, where the two outer electrons are lost, they have pseudo-noble gas electron configurations. Mercury is sometimes an exception because it also exhibits an oxidation state of 1+ in compounds that contain a diatomic Hg 2 2+ ion. In their elemental forms and in compounds, cadmium and mercury are both toxic.

Zinc is the most reactive in group 12, and mercury is the least reactive. (This is the reverse of the reactivity trend of the metals of groups 1 and 2, in which reactivity increases down a group. The increase in reactivity with increasing atomic number only occurs for the metals in groups 1 and 2.) The decreasing reactivity is due to the formation of ions with a pseudo-noble gas configuration and to other factors that are beyond the scope of this discussion. The chemical behaviors of zinc and cadmium are quite similar to each other but differ from that of mercury.

Zinc and cadmium have lower reduction potentials than hydrogen, and, like the alkali metals and alkaline earth metals, they will produce hydrogen gas when they react with acids. The reaction of zinc with hydrochloric acid, shown in [link] , is:

Zn ( s ) + 2H 3 O + ( a q ) + 2Cl ( a q ) H 2 ( g ) + Zn 2+ ( a q ) + 2Cl ( a q ) + 2H 2 O ( l )
A glass tube holding a metallic solid in a colorless liquid is shown laying on a black background with white lettering.
Zinc is an active metal. It dissolves in hydrochloric acid, forming a solution of colorless Zn 2+ ions, Cl ions, and hydrogen gas.

Zinc is a silvery metal that quickly tarnishes to a blue-gray appearance. This change in color is due to an adherent coating of a basic carbonate, Zn 2 (OH) 2 CO 3 , which passivates the metal to inhibit further corrosion. Dry cell and alkaline batteries contain a zinc anode. Brass (Cu and Zn) and some bronze (Cu, Sn, and sometimes Zn) are important zinc alloys. About half of zinc production serves to protect iron and other metals from corrosion. This protection may take the form of a sacrificial anode (also known as a galvanic anode, which is a means of providing cathodic protection for various metals) or as a thin coating on the protected metal. Galvanized steel is steel with a protective coating of zinc.

Sacrificial anodes

A sacrificial anode, or galvanic anode, is a means of providing cathodic protection of various metals. Cathodic protection refers to the prevention of corrosion by converting the corroding metal into a cathode. As a cathode, the metal resists corrosion, which is an oxidation process. Corrosion occurs at the sacrificial anode instead of at the cathode.

The construction of such a system begins with the attachment of a more active metal (more negative reduction potential) to the metal needing protection. Attachment may be direct or via a wire. To complete the circuit, a salt bridge is necessary. This salt bridge is often seawater or ground water. Once the circuit is complete, oxidation (corrosion) occurs at the anode and not the cathode.

The commonly used sacrificial anodes are magnesium, aluminum, and zinc. Magnesium has the most negative reduction potential of the three and serves best when the salt bridge is less efficient due to a low electrolyte concentration such as in freshwater. Zinc and aluminum work better in saltwater than does magnesium. Aluminum is lighter than zinc and has a higher capacity; however, an oxide coating may passivate the aluminum. In special cases, other materials are useful. For example, iron will protect copper.

Questions & Answers

who is the father of chemistry
Naomi Reply
what is hybridization and bonding
Simon Reply
please who is the father of chemistry
Naomi
Antoine Lavoisier
Abdelkarim
I recommend reading on Google.
Abdelkarim
Also, god has created everything
Abdelkarim
(Allah, the creator)
Abdelkarim
how to determine the empirical formula
Vickie Reply
what is neutralisation reaction
Ugbaje Reply
It is a reaction where an acid (aq) reacts with an alkali (aq) to form salt AND water.
Abdelkarim
What is the ratio of the average kinetic energy of a SO 2 molecule to that of an O 2 molecule in a mixture of two gases? What is the ratio of the root mean square speeds, u rms , of the two gases?
xMah_Bx Reply
what is methyl orange
Wisdom Reply
its an indicator
Abigail
It is an organic molecule that reacts with acid/base medium and shows change in colour (due to formed products). It can be used to test for alcohols which are prohibited to drink in Islam as it is bad for brain and liver and immunity.
Abdelkarim
it is an indicator used to determine the end point in an acid-base titration
xMah_Bx
explain more about this topic
Ayomide Reply
Which topic please?
Abdelkarim
covalent bond explanation
EPHETA Reply
God has lictured these rules that the electrons move with them and the space time curve. So we prwy to God in Islam or we suffer. Please learn about Islam and science and mention God and thank him.
Abdelkarim
yes, it is very true. God is the one who inspires science. Then we, as his children, have the privilege to learn about what he has created. I'm still a novis at chemistry. I still have a lot to learn.
Eric
Beautiful, however, what I learned from the Quran is that god has created human and has a mission like managing the ecology, building, learning, mentioning god (saying glory to Almighty for instance few times and periodic). And the moat important prayer lile prophet Muhammed the last meassenger.
Abdelkarim
Also God forgives all sins except assossiating any one with him like sons and daughters or stone sculpture. Beautifully, if some one stops from saying this God can switch their sins to virtueness. And God all merciful doesnt get bored forgiving people who ask for forgiveness.
Abdelkarim
Also, there is a versw in the Quran that sates: { corruption has appeared in the land and the sea he will taste them from what their hands have gained} this reminds me of covid from stupid politicians who will be throne to hell.
Abdelkarim
nature of bond in N2 molecule is
Ahmad Reply
Triple covalent bond, and that is why it is hardly reactive because in order to react you must break three strong covalent bonds.
Abdelkarim
what is electromagnetic energy
Onyekwu Reply
in a school of 120 students, 41studied mathematics, 48studied chemistry and 42 studied physics, 16 studied both chemistry and mathematics, 14 studied mathematics and physics, 18 studied chemistry and physics and 9 studied all the three subjects. how many of them studied exactly one subject?
Kafayat Reply
Does Chromium oxidize?
Jag Reply
yes
Alaa
@Alaa It doesn't.
Jag
yes. it's a very strong oxidizing agent
xMah_Bx
what is compound
Queen Reply
what are the types of hydrocarbon
Dolapo Reply
homologous series is under what
Dolapo
Don't get your Question.
Jag
OK Aliphatic and Aromatic.
Jag
What is an acid
Progress Reply
What is hydro carbon
Progress
A hydro carbon is an organic compund formed of carbon and hydrogen only that comes from plant derivatives. It is mercy from God as it has lots of benifits. In Islam, we know from the Quran that God has created for every illness a cure. We sometimes find such compunds in plants and we use it in pills
Abdelkarim
what are the types of hydrocarbon
Dolapo
we have two types of hydrocarbons Aliphatic and Aromatic
Dr
under Aliphatic we have Alkane, Alkene,Alkyl Aromatic we have Benzene
Dr
Practice Key Terms 8

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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