chemistry

Hexol

Hexol 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 Hexol rather than just read about it. In short: In chemistry, hexol is a cation with formula {[Co(NH3)4(OH)2]3Co}6+ — a coordination complex consisting of four cobalt cations in oxidation state +3, twelve ammonia molecules NH3, and six hydroxy anions HO−, with a net charge of +6. The hydroxy groups act as bridges between the central cobalt atom and the other three, which carry the ammonia ligands.

Key takeaways

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

Reference excerpt

In chemistry, hexol is a cation with formula {[Co(NH3)4(OH)2]3Co}6+ — a coordination complex consisting of four cobalt cations in oxidation state +3, twelve ammonia molecules NH3, and six hydroxy anions HO−, with a net charge of +6. The hydroxy groups act as bridges between the central cobalt atom and the other three, which carry the ammonia ligands. Salts of hexol, such as the sulfate {[Co(NH3)4(OH)2]3Co}(SO4)3(H2O)x, are of historical significance as the first synthetic non-carbon-containing chiral compounds.

Preparation Salts of hexol were first described by Jørgensen, although it was Werner who recognized its structure. The cation is prepared by heating a solution containing the cis-diaquotetramminecobalt(III) cation [Co(NH3)4(H2O)2]3+ with a dilute base:

4 [Co(NH3)4(H2O)2]3+ + 2 HO− → {[Co(NH3)4(OH)2]3Co}6+ + 4 NH4+ + 4 H2O

Hexol sulfate Starting with the sulfate and using ammonium hydroxide as the base, depending on the conditions, one obtains the 9-hydrate, the 6-hydrate, or the 4-hydrate of hexol sulfate. These salts form dark brownish-violet or black tabular crystals, with low solubility in water. When treated with concentrated hydrochloric acid, hexol sulfate converts to cis-diaquotetramminecobalt(III) sulfate. In boiling dilute sulfuric acid, hexol sulfate further degrades with evolution of oxygen and nitrogen.

Optical properties The hexol cation exists as two optical isomers that are mirror images of each other, depending on the arrangement of the bonds between the central cobalt atom and the three bidentate peripheral units [Co(NH3)4(HO)2]. It belongs to the D3 point group. The nature of chirality can be compared to that of the ferrioxalate anion [Fe(C2O4)3]3−. In a historic set of experiments, a salt of hexol with an optically active anion — specifically, its D-(+)-bromocamphorsulfonate – was resolved into separate salts of the two cation isomers by fractional crystallisation. A more efficient resolution involves the bis(tartrato)diantimonate(III) anion. The hexol hexacation has a high specific rotation of 2640°.

"Second hexol" Werner also described a second achiral hexol (a minor byproduct from the production of Fremy's salt) that he incorrectly identified as a linear tetramer. The second hexol is hexanuclear (contains six cobalt centres in each ion), not tetranuclear. Its point group is C2h, and its formula is [Co6(NH3)14(OH)8O2]6+, whereas that of hexol is [Co4(NH3)12(OH)6]6+.

References

External links Hexol Molecule of the Month September 1997 Website National Pollutant Inventory – Cobalt fact sheet

Illustrations

Worked examples

Example 1 — a first encounter with Hexol

Start with the simplest possible case. Write down what Hexol 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 Hexol 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 Hexol 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 Hexol

In research: Hexol 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 Hexol 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: Hexol is common in secondary-school and first-year university syllabi. It links to neighbouring topics Ammine complexes, Cobalt(III) compounds, Cobalt complexes, so understanding it makes those chapters shorter.
In everyday life: Look for Hexol 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 Hexol in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hexol 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 Hexol out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hexol in simple terms?

Why does Hexol 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 Hexol?

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 Hexol.