chemistry

Iron(II) chloride

Iron(II) chloride is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Iron(II) chloride rather than just read about it. In short: Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point.

Key takeaways

Iron(II) chloride belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Iron(II) chloride to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Iron(II) chloride from memory before moving on to harder problems.

Reference excerpt

Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is highly soluble in water, giving pale green solutions.

Production

Hydrated forms of ferrous chloride are generated by treatment of wastes from steel production with hydrochloric acid. Such solutions are designated "spent acid," or "pickle liquor" especially when the hydrochloric acid is not completely consumed:

Fe + 2 HCl → FeCl2 + H2 The production of ferric chloride involves the use of ferrous chloride. Ferrous chloride is also a byproduct from the production of titanium, since some titanium ores contain iron.

Anhydrous FeCl2 Ferrous chloride is prepared by addition of iron powder to a solution of hydrochloric acid in methanol. This reaction gives the methanol solvate of the dichloride, which upon heating in a vacuum at about 160 °C converts to anhydrous FeCl2. The net reaction is shown:

Fe + 2 HCl → FeCl2 + H2 FeBr2 and FeI2 can be prepared analogously. An alternative synthesis of anhydrous ferrous chloride is the reduction of FeCl3 with chlorobenzene:

2 FeCl3 + C6H5Cl → 2 FeCl2 + C6H4Cl2 + HCl For the preparation of ferrocene ferrous chloride is generated in situ by comproportionation of FeCl3 with iron powder in tetrahydrofuran (THF). Ferric chloride decomposes to ferrous chloride at high temperatures.

Hydrates The dihydrate, FeCl2(H2O)2, crystallizes from concentrated hydrochloric acid. The dihydrate is a coordination polymer. Each Fe center is coordinated to four doubly bridging chloride ligands. The octahedron is completed by a pair of mutually trans aquo ligands.

Reactions

FeCl2 and its hydrates form complexes with many ligands. For example, solutions of the hydrates react with two molar equivalents of [(C2H5)4N]Cl to give the salt [(C2H5)4N]2[FeCl4]. The anhydrous FeCl2, which is soluble in THF, is a standard precursor in organometallic synthesis. FeCl2 is used to generate NHC complexes in situ for cross coupling reactions.

Applications Unlike the related ferrous sulfate and ferric chloride, ferrous chloride has few commercial applications. Aside from use in the laboratory synthesis of iron complexes, ferrous chloride serves as a coagulation and flocculation agent in wastewater treatment, especially for wastes containing chromate or sulfides. It is used for odor control in wastewater treatment. It is used as a precursor to make various grades of hematite that can be used in a variety of pigments. It is the precursor to hydrated iron(III) oxides that are magnetic pigments. FeCl2 finds some use as a reagent in organic synthesis.

Natural occurrence Lawrencite, (Fe,Ni)Cl2, is the natural counterpart, and a typically (though rarely occurring) meteoritic mineral. The natural form of the dihydrate is rokühnite - a very rare mineral. Related, but more complex (in particular, basic or hydrated) minerals are hibbingite, droninoite and kuliginite.

References

See also Iron(III) chloride Iron(II) sulfate

Illustrations

Worked examples

Example 1 — a first encounter with Iron(II) chloride

Start with the simplest possible case. Write down what Iron(II) chloride claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Iron(II) chloride before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Iron(II) chloride ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Iron(II) chloride

In research: Iron(II) chloride appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Iron(II) chloride in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Iron(II) chloride is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chlorides, Iron(II) compounds, Metal halides, so understanding it makes those chapters shorter.
In everyday life: Look for Iron(II) chloride outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Iron(II) chloride in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Iron(II) chloride means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Iron(II) chloride out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Iron(II) chloride in simple terms?

Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point.

Why does Iron(II) chloride matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Iron(II) chloride?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Iron(II) chloride.