chemistry

Acidic oxide

Acidic oxide 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 Acidic oxide rather than just read about it. In short: An acidic oxide is an oxide that either produces an acidic solution upon addition to water, or acts as an acceptor of hydroxide ions effectively functioning as a Lewis acid. Acidic oxides will typically have a low pKa and may be inorganic or organic.

Key takeaways

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

Reference excerpt

An acidic oxide is an oxide that either produces an acidic solution upon addition to water, or acts as an acceptor of hydroxide ions effectively functioning as a Lewis acid. Acidic oxides will typically have a low pKa and may be inorganic or organic. A commonly encountered acidic oxide, carbon dioxide produces an acidic solution (and the generation of carbonic acid) when dissolved. Generally non-metallic oxides are acidic. The acidity of an oxide can be reasonably assumed by its accompanying constituents. Less electronegative elements tend to form basic oxides such as sodium oxide and magnesium oxide, whereas more electronegative elements tend to produce acidic oxides such as carbon dioxide and phosphorus pentoxide. Some oxides, like aluminium oxides, are amphoteric, while some oxides may be neutral.

Acidic oxides are of environmental concern. Sulfur and nitrogen oxides are considered air pollutants as they react with atmospheric water vapour to produce acid rain.

Examples Carbonic acid is an illustrative example of the Lewis acidity of an acidic oxide.

CO2 + 2OH− ⇌ HCO3− + OH− ⇌ CO32− + H2O This property is a key reason for keeping alkali chemicals well sealed from the atmosphere, as long-term exposure to carbon dioxide in the air can degrade the material.

Carbon dioxide is also the anhydride of carbonic acid: H2CO3 → H2O + CO2 Chromium trioxide, which reacts with water forming chromic acid: CrO3 + H2O → H2CrO4 Dinitrogen pentoxide, which reacts with water forming nitric acid: N2O5 + H2O → 2 HNO3 Manganese heptoxide, which reacts with water forming permanganic acid: Mn2O7 + H2O → 2 HMnO4

Further examples

Aluminium oxide Aluminium oxide (Al2O3) is an amphoteric oxide; it can act as a base or acid. For example, with base different aluminate salts will be formed:

Al2O3 + 2 NaOH + 3 H2O → 2 NaAl(OH)4

Silicon dioxide Silicon dioxide is an acidic oxide. It will react with strong bases to form silicate salts. Silicon dioxide is the anhydride of silicic acid:

H4SiO4 → 2 H2O + SiO2

Phosphorus oxides Phosphorus(III) oxide reacts to form phosphorous acid in water:

P4O6 + 6 H2O → 4 H3PO3 Phosphorus(V) oxide reacts with water to give phosphoric acid:

P4O10 + 6 H2O → 4 H3PO4

Sulfur oxides Sulfur dioxide reacts with water to form the weak acid, sulfurous acid:

SO2 + H2O → H2SO3 Sulfur trioxide forms the strong acid sulfuric acid with water:

SO3 + H2O → H2SO4 This reaction is important in the manufacturing of sulfuric acid.

Chlorine oxides Chlorine(I) oxide reacts with water to form hypochlorous acid, a very weak acid:

Cl2O + H2O ⇌ 2 HOCl Chlorine(VII) oxide reacts with water to form perchloric acid, a strong acid:

Cl2O7 + H2O → 2 HClO4

Iron oxides Iron(II) oxide is the anhydride of the aqueous ferrous ion:

[Fe(H2O)6]2+ → FeO + 2 H+ + 5 H2O

Chromium oxides Chromium trioxide is the anhydride of chromic acid:

H2CrO4 → H2O + CrO3

Vanadium oxides Vanadium trioxide is the anhydride of vanadous acid:

2H3VO3 → 3H2O + V2O3 Vanadium pentoxide is the anhydride of vanadic acid:

2H3VO4 → 3H2O + V2O5

See also Organic acid anhydride, similar compounds in organic chemistry Base anhydride

References Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.

Worked examples

Example 1 — a first encounter with Acidic oxide

Start with the simplest possible case. Write down what Acidic oxide 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 Acidic oxide 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 Acidic oxide 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 Acidic oxide

In research: Acidic oxide 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 Acidic oxide 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: Acidic oxide is common in secondary-school and first-year university syllabi. It links to neighbouring topics Acidic oxides, so understanding it makes those chapters shorter.
In everyday life: Look for Acidic oxide 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 Acidic oxide in 20 minutes

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

Frequently asked questions

What is Acidic oxide in simple terms?

Why does Acidic oxide 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 Acidic oxide?

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 Acidic oxide.