Weird Science

Cobalt(II) Chloride and Its Paramagnetic Behavior

Polish ver­sion is here

Not Only Iron

Most peo­ple are fami­liar with the magne­tic pro­per­ties of iron. It belongs to a class of sub­stan­ces known as fer­ro­ma­gnets. Such sub­stan­ces exhi­bit spon­ta­ne­ous magne­ti­za­tion. Fer­ro­ma­gne­tism is one of the stron­gest forms of magne­tism and is respon­si­ble for most magne­tic phe­no­mena enco­un­te­red in eve­ry­day life. In addi­tion to iron, fer­ro­ma­gnets inc­lude cobalt, nic­kel, and, at lower tem­pe­ra­tu­res, gado­li­nium, ter­bium, dys­pro­sium, hol­mium, and erbium. Besi­des ele­ments, many alloys and che­mi­cal com­po­unds also exhi­bit these pro­per­ties.

Apart from fer­ro­ma­gne­tism, there are other types of magne­tic inte­rac­tions, one of which is para­ma­gne­tism. This term refers to a mate­rial beco­ming magne­ti­zed in the direc­tion of an exter­nal magne­tic field. A para­ma­gne­tic mate­rial is attrac­ted to a magnet, altho­ugh much more wea­kly than a fer­ro­ma­gnet.

There are many para­ma­gne­tic sub­stan­ces, such as liquid oxy­gen, sodium, pla­ti­num, nitric oxide (II), heme, and alu­mi­num. Howe­ver, para­ma­gne­tic inte­rac­tions are usu­ally very weak and dif­fi­cult to obse­rve without spe­cia­li­zed equ­ip­ment. Howe­ver, hydra­ted cobalt(II) chlo­ride exhi­bits a rela­ti­vely strong effect, making it easier to obse­rve this phe­no­me­non.

Expe­ri­ment

We need a cobalt salt, spe­ci­fi­cally cobalt(II) chlo­ride hexa­hy­drate CoCl2·6H2O. This com­po­und appe­ars as dark red cry­stals, as shown below.

Ilustracja: hydrated cobalt(II) chloride

hydrated cobalt(II) chloride

War­ning: Cobalt(II) chlo­ride CoCl2 is car­ci­no­ge­nic! Avoid any con­tact with eyes or skin! The author takes no respon­si­bi­lity for any poten­tial damage or harm. You pro­ceed at your own risk!

We also need a magnet; a small neo­dy­mium magnet works best.

Ilustracja: neodymium magnet

neodymium magnet

Take a few small cry­stals of CoCl2·6H2O, bring the magnet close, and obse­rve whe­ther they inte­ract. You can obse­rve the effect in my video:

Sur­pri­sin­gly, the cry­stals of a sub­stance unre­la­ted to iron are cle­arly attrac­ted to the magnet!

Ilustracja:

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Expla­na­tion

Para­ma­gne­tic mate­rials have at least one unpa­i­red elec­tron, which results in an exter­nal magne­tic moment for each atom. Without an exter­nal magne­tic field, the vec­tors of these ele­men­tary magne­tic moments are ran­domly orien­ted thro­u­ghout the mate­rial, resul­ting in a net zero magne­tic moment for the entire body.

The cause of para­ma­gne­tism is the ali­gn­ment of the elec­tron spins in the mate­rial along the lines of the exter­nal magne­tic field, altho­ugh ther­mal vibra­tions of the mole­cu­les coun­te­ract this ali­gn­ment. At low tem­pe­ra­tu­res and in strong magne­tic fields, nearly all the magne­tic dipo­les of the elec­trons become ali­gned, cau­sing their moments to align and pro­duce an obse­rva­ble exter­nal magne­tic moment.

The magne­tic per­me­a­bi­lity μ of para­ma­gne­tic mate­rials is only sli­gh­tly gre­a­ter than one, mea­ning that they sli­gh­tly enhance the exter­nal magne­tic field.

A para­ma­gne­tic mate­rial exhi­bits no magne­tic pro­per­ties without an exter­nal field. This means that it can­not be per­ma­nen­tly magne­ti­zed, unlike fer­ro­ma­gne­tic mate­rials. Ano­ther type of magne­tic inte­rac­tion is dia­ma­gne­tism.

Enjoy!

Fur­ther rea­dings:

Marek Ples

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