chemistry

Iodic acid

Iodic 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 Iodic acid rather than just read about it. In short: Iodic acid is a white water-soluble solid with the chemical formula HIO3. Its robustness contrasts with the instability of chloric acid and bromic acid.

Key takeaways

Iodic 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 Iodic acid to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Iodic acid from memory before moving on to harder problems.

Reference excerpt

Iodic acid is a white water-soluble solid with the chemical formula HIO3. Its robustness contrasts with the instability of chloric acid and bromic acid. Iodic acid features iodine in the oxidation state +5 and is one of the most stable oxo-acids of the halogens. When heated, samples dehydrate to give iodine pentoxide. On further heating, the iodine pentoxide further decomposes, giving a mix of iodine and oxygen vapors.

Preparation Iodic acid can be produced by oxidizing iodine with strong oxidizers such as nitric acid, chlorine, chloric acid or hydrogen peroxide, for example:

I2 + 6 H2O + 5 Cl2 ⇌ 2 HIO3 + 10HCl Iodic acid is also produced by the hydrolysis of iodine chlorides,

5 ICl + 3 H2O → 5 HCl + HIO3 + 2 I2 5 ICl3 + 9 H2O → 15 HCl + 3 HIO3 + I2 although all methods involving chlorine in acidic conditions produce tetrachloroiodic acid as a byproduct:

HIO3 + 6 HCl ⇌ HICl4 + Cl2 + 3 H2O

Structure Iodic acid crystallises from acidic solution as orthorhombic α-HIO3 in space group P212121. The structure consists of pyramidal molecules linked by hydrogen bonding and intermolecular iodine-oxygen interactions. The I=O bond lengths are 1.81 Å while the I–OH distance is 1.89 Å. Several other polymorphs have been reported, including an orthorhombic γ form in space group Pbca and an orthorhombic δ form in space group P212121. All of the polymorphs contain pyramidal molecules, hydrogen bonding and I···O interactions, but differ in packing arrangement.

Properties Iodic acid is a relatively strong acid with a pKa of 0.75. It is strongly oxidizing in acidic solution, less so in basic solution. When iodic acid acts as oxidizer, then the product of the reaction is either elemental iodine or the iodide ion. Under some special conditions (very low pH and high concentration of chloride ions, such as in concentrated hydrochloric acid), iodic acid is reduced to iodine trichloride, a golden yellow compound which is present in solution as tetrachloroiodic acid. In the absence of chloride ions, when there is an excess amount of reductant, then all iodate is converted to iodide ion. When there is an excess amount of iodate, then part of the iodate is converted to iodine.

Uses Iodic acid is used as a strong acid (though it is not truly a strong acid, but a weak acid that is very close to being a strong acid) in analytical chemistry. It may be used to standardize solutions of both weak and strong bases, using methyl red or methyl orange as the indicator.

Use in salt industry Iodic acid can be used to synthesize sodium or potassium iodate for increasing iodine content of salt.

Other oxyacids Iodic acid is part of a series of oxyacids in which iodine can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known.

References

Illustrations

Worked examples

Example 1 — a first encounter with Iodic acid

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

In research: Iodic 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 Iodic 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: Iodic acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Analytical standards, Halogen oxoacids, Iodates, so understanding it makes those chapters shorter.
In everyday life: Look for Iodic 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.

Affiliate

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

How to study Iodic acid in 20 minutes

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

Frequently asked questions

What is Iodic acid in simple terms?

Iodic acid is a white water-soluble solid with the chemical formula HIO3. Its robustness contrasts with the instability of chloric acid and bromic acid.

Why does Iodic 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 Iodic 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 Iodic acid.