chemistry

Selenic acid

Selenic acid 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 Selenic acid rather than just read about it. In short: Selenic acid is the inorganic compound with the formula H2SeO4. It is an oxoacid of selenium, and its structure is more accurately described as O2Se(OH)2.

Key takeaways

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

Reference excerpt

Selenic acid is the inorganic compound with the formula H2SeO4. It is an oxoacid of selenium, and its structure is more accurately described as O2Se(OH)2. It is a colorless compound. Although it has few uses, one of its salts, sodium selenate is used in the production of glass and animal feeds.

Structure and bonding The molecule is tetrahedral, as predicted by VSEPR theory. The Se–O bond length is 161 pm. In the solid state, it crystallizes in an orthorhombic structure.

Preparation It is prepared by oxidising selenium compounds in lower oxidation states. One method involves the oxidation of selenium dioxide with hydrogen peroxide:

SeO2 + H2O2 → H2SeO4 Unlike the production of sulfuric acid by hydration of sulfur trioxide, the hydration of selenium trioxide is an impractical method. Instead, selenic acid may also be prepared by the oxidation of selenous acid (H2SeO3) with halogens, such as chlorine or bromine, or with potassium permanganate. Using chlorine or bromine as the oxidising agents also produces hydrochloric or hydrobromic acid as a side-product, which needs to be removed from the solution since they can reduce the selenic acid to selenous acid. To obtain the anhydrous acid as a crystalline solid, the resulting solution is evaporated at temperatures below 140 °C (413 K; 284 °F) in a vacuum.

Reactions Like sulfuric acid, selenic acid is a strong acid that is hygroscopic and extremely soluble in water. Concentrated solutions are viscous. Crystalline mono- and di-hydrates are known. The monohydrate melts at 26 °C, and the dihydrate melts at −51.7 °C. Selenic acid is a stronger oxidizer than sulfuric acid, capable of liberating chlorine from chloride ions, being reduced to selenous acid in the process:

H2SeO4 + 2 H+ + 2 Cl− → H2SeO3 + H2O + Cl2 It decomposes above 200 °C, liberating oxygen gas and being reduced to selenous acid:

2 H2SeO4 → 2 H2SeO3 + O2 Selenic acid reacts with barium salts to precipitate solid BaSeO4, analogous to the sulfate. In general, selenate salts resemble sulfate salts, but are more soluble. Many selenate salts have the same crystal structure as the corresponding sulfate salts. Treatment with fluorosulfuric acid gives selenoyl fluoride:

H2SeO4 + 2 HSO3F → SeO2F2 + 2 H2SO4 Hot, concentrated selenic acid reacts with gold, forming a reddish-yellow solution of gold(III) selenate:

2 Au + 6 H2SeO4 → Au2(SeO4)3 + 3 H2SeO3 + 3 H2O

Applications Selenic acid is used as a specialized oxidizing agent.

References

Illustrations

Worked examples

Example 1 — a first encounter with Selenic acid

Start with the simplest possible case. Write down what Selenic acid 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 Selenic acid 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 Selenic acid 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 Selenic acid

In research: Selenic acid 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 Selenic acid 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: Selenic acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chalcogen oxoacids, Oxidizing acids, Selenates, so understanding it makes those chapters shorter.
In everyday life: Look for Selenic acid 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Selenic acid” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Selenic acid in 20 minutes

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

Frequently asked questions

What is Selenic acid in simple terms?

Selenic acid is the inorganic compound with the formula H2SeO4. It is an oxoacid of selenium, and its structure is more accurately described as O2Se(OH)2.

Why does Selenic acid 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 Selenic acid?

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 Selenic acid.