science

Manganate

Manganate is a science 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 Manganate rather than just read about it. In short: In inorganic nomenclature, a manganate is any negatively charged molecular entity with manganese as the central atom. However, the name is usually used to refer to the tetraoxidomanganate(2−) anion, MnO42–, also known as manganate(VI) because it contains manganese in the +6 oxidation state.

Key takeaways

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

Reference excerpt

In inorganic nomenclature, a manganate is any negatively charged molecular entity with manganese as the central atom. However, the name is usually used to refer to the tetraoxidomanganate(2−) anion, MnO42–, also known as manganate(VI) because it contains manganese in the +6 oxidation state. Manganates are the only known manganese(VI) compounds. Other manganates include hypomanganate or manganate(V), MnO43–, permanganate or manganate(VII), MnO4–, and the dimanganate or dimanganate(III) Mn2O66–. A manganate(IV) anion MnO44– has been prepared by radiolysis of dilute solutions of permanganate. It is mononuclear in dilute solution, and shows a strong absorption in the ultraviolet and a weaker absorption at 650 nm.

Structure

The manganate(VI) ion is tetrahedral, similar to sulfate or chromate: indeed, manganates are often isostructural with sulfates and chromates, a fact first noted by Eilhard Mitscherlich in 1831. The manganese–oxygen distance is 165.9 pm, about 3 pm longer than in permanganate. As a d1 ion it is paramagnetic and should exhibit Jahn–Teller distortion, but any deviation from the tetrahedral geometry is too small to be detected by X-ray crystallography. Manganates are dark green in colour, with a visible absorption maximum of λmax = 606 nm (ε = 1710 dm3 mol−1 cm−1). The Raman spectrum has also been reported.

Preparation Sodium and potassium manganates are usually prepared in the laboratory by stirring the equivalent permanganate in a concentrated solution (5–10 M) of the hydroxide for 24 hours or with heating.

4 MnO4– + 4 OH− → 4 MnO42– + 2 H2O + O2 Potassium manganate is prepared industrially, as an intermediate to potassium permanganate, by dissolving manganese dioxide in molten potassium hydroxide with potassium nitrate or air as the oxidizing agent.

2 MnO2 + 4 OH− + O2 → 2 MnO42– + 2 H2O

Disproportionation Manganates are unstable towards disproportionation in all but the most alkaline of aqueous solutions. The ultimate products are permanganate and manganese dioxide, but the kinetics are complex and the mechanism may involve protonated and/or manganese(V) species.

Uses Manganates, particularly the insoluble barium manganate, BaMnO4, have been used as oxidizing agents in organic synthesis: they will oxidize primary alcohols to aldehydes and then to carboxylic acids, and secondary alcohols to ketones. Barium manganate has also been used to oxidize hydrazones to diazo compounds.

Related compounds Manganate is formally the conjugate base of hypothetical manganic acid H2MnO4, which cannot be formed because of its rapid disproportionation. However, its second acid dissociation constant has been estimated by pulse radiolysis techniques:

HMnO4– ⇌ MnO42– + H+ pKa = 7.4 ± 0.1

Manganites The name "manganite" is used for compounds formerly believed to contain the anion MnO33–, with manganese in the +3 oxidation state. However, most of these "manganites" do not contain discrete oxyanions, but are mixed oxides with perovskite (LaMnIIIO3, CaMnIVO3), spinel (LiMn2III,IVO4) or sodium chloride (LiMnIIIO2, NaMnIIIO2) structures. One exception is potassium dimanganate(III), K6Mn2O6, which contains discrete Mn2O66– anions.

References

Illustrations

Worked examples

Example 1 — a first encounter with Manganate

Start with the simplest possible case. Write down what Manganate claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Manganate 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 Manganate 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 Manganate

In research: Manganate appears in science 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 Manganate 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: Manganate is common in secondary-school and first-year university syllabi. It links to neighbouring topics Manganates, Oxometallates, Transition metal oxyanions, so understanding it makes those chapters shorter.
In everyday life: Look for Manganate 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 Manganate in 20 minutes

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

Frequently asked questions

What is Manganate in simple terms?

Why does Manganate matter?

Because it connects several science 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 Manganate?

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 Manganate.