Silicic acid

Key takeaways

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

Reference excerpt

In chemistry, a silicic acid () is any chemical compound containing the element silicon attached to oxide (=O) and hydroxyl (−OH) groups, with the general formula [H2xSiOx+2]n or, equivalently, [SiOx(OH)4−2x]n. Orthosilicic acid is a representative example. Silicic acids are not observed in isolation, but are thought to exist in aqueous solutions, including seawater, and play a role in biomineralization. They are typically colorless weak acids that are sparingly soluble in water. Depending on the number of silicon atoms present, there are mono- and polysilicic (di-, tri-, tetrasilicic, etc.) acids. Like the silicate anions, which are their better known conjugate bases, silicic acids are proposed to be oligomeric or polymeric. Monomeric silicic acids are primarily of theoretical interest, since they have never been identified in a well-defined form characterized by X-ray crystallography.

Examples

Reactions Silicic acids can be seen as hydrated forms of silica, namely 2 H2xSiOx+2 = SiO2·(H2O)x. Indeed, in concentrated solutions, silicic acids generally polymerize and condense, and ultimately degrade to silicon dioxide and water. The intermediate stages may be very thick liquids or gel-like solids. Dehydrating the latter yields a hard translucent form of silica with atomic-scale pores, called silica gel, which is widely used as water absorbent and drying agent. Silica dissolves very sparingly in water and is present in seawater at concentrations below 100 parts per million. In such dilute solutions, silica is assumed to exist as orthosilicic acid. Theoretical computations indicate that the dissolution of silica in water proceeds through the formation of a SiO2·2H2O complex and then orthosilicic acid. The silicon–oxygen double bond of metasilicic acid, implied by the formula H2SiO3, is hypothetical or highly unstable. Such double bonds can be hydrated to a pair of hydroxyl (−OH) groups:

= Si = O + H 2 O ⟷ = Si ( − OH ) 2 {\displaystyle {\ce {=Si=O + H2O <-> =Si(-OH)2}}}

For example,

H 2 SiO 3 metasilicic acid + H 2 O ⟷ H 4 SiO 4 orthosilicic acid {\displaystyle {\ce {{\overset {metasilicic\ acid}{H2SiO3}}+H2O<->{\overset {orthosilicic\ acid}{H4SiO4}}}}}

or

H 2 Si 2 O 5 disilicic acid + 2 H 2 O ⟷ ( HO ) 3 Si − O − Si ( OH ) 3 pyrosilicic acid {\displaystyle {\ce {{\overset {disilicic\ acid}{H2Si2O5}}+2H2O<->{\overset {pyrosilicic\ acid}{(HO)3Si-O-Si(OH)3}}}}}

Alternatively, metasilicic acid is liable to form cyclic polymers [−SiO(OH)2−]n, which can be opened by hydration to chain polymers HO[−SiO(OH)2−]nH. Similarly, disilicic acid is liable to form complex polymers with a tetravalent unit, [=Si2O3(OH)2=]n. Conversely, oligomeric and polymeric acids may depolymerize by hydrolysis of the Si−O−Si bridges, or such bridges may be created by condensation:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Silicic acid

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

In research: Silicic 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 Silicic 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: Silicic acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Inorganic adamantogen oxoacids, Silanols, Silicon compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Silicic 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.

How to study Silicic acid in 20 minutes

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

Frequently asked questions

What is Silicic acid in simple terms?

In chemistry, a silicic acid () is any chemical compound containing the element silicon attached to oxide (=O) and hydroxyl (−OH) groups, with the general formula [H2xSiOx+2]n or, equivalently, [SiOx(OH)4−2x]n. Orthosilicic acid is a representative example.

Why does Silicic 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 Silicic 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 Silicic acid.