chemistry

Phosphoric acids and phosphates

Phosphoric acids and phosphates 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 Phosphoric acids and phosphates rather than just read about it. In short: In chemistry, a phosphoric acid, in the general sense, is a phosphorus oxoacid in which each phosphorus (P) atom is in the oxidation state +5, and is bonded to four oxygen (O) atoms, one of them through a double bond, arranged as the corners of a tetrahedron. Two or more of these PO4 tetrahedra may be connected by shared single-bonded oxygens, forming linear or branched chains, cycles, or more complex structures.

Key takeaways

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

Reference excerpt

In chemistry, a phosphoric acid, in the general sense, is a phosphorus oxoacid in which each phosphorus (P) atom is in the oxidation state +5, and is bonded to four oxygen (O) atoms, one of them through a double bond, arranged as the corners of a tetrahedron. Two or more of these PO4 tetrahedra may be connected by shared single-bonded oxygens, forming linear or branched chains, cycles, or more complex structures. The single-bonded oxygen atoms that are not shared are completed with acidic hydrogen atoms. The general formula of a phosphoric acid is Hn+2−2xPnO3n+1−x, where n is the number of phosphorus atoms and x is the number of fundamental cycles in the molecule's structure, between 0 and ⁠n + 2/2⁠.

Removal of protons (H+) from k hydroxyl groups –OH leaves anions generically called phosphates (if k = n − 2x + 2) or hydrogen phosphates (if k is between 1 and n − 2x + 1), with general formula [Hn−2x+2−kPnO3n+1−x]k−. The fully dissociated anion (k = n − 2x + 2) has formula [PnO3n−x+1](n−2x+2)−. The term phosphate is also used in organic chemistry for the functional groups that result when one or more of the hydrogens are replaced by bonds to other groups. These acids, together with their salts and esters, include some of the best-known compounds of phosphorus, of high importance in biochemistry, mineralogy, agriculture, pharmacy, chemical industry, and chemical research.

Acids

Phosphoric acid

The simplest and most commonly encountered of the phosphoric acids is orthophosphoric acid, H3PO4. Indeed, the term phosphoric acid often means this compound specifically (and this is also the current IUPAC nomenclature).

Oligophosphoric and polyphosphoric acids

Two or more orthophosphoric acid molecules can be joined by condensation into larger molecules by elimination of water. Condensation of a few units yields the oligophosphoric acids, while larger molecules are called polyphosphoric acids. (However, the distinction between the two terms is not well defined.) For example, pyrophosphoric, triphosphoric and tetraphosphoric acids can be obtained by the reactions

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Illustrations

Worked examples

Example 1 — a first encounter with Phosphoric acids and phosphates

Start with the simplest possible case. Write down what Phosphoric acids and phosphates 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 Phosphoric acids and phosphates 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 Phosphoric acids and phosphates 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 Phosphoric acids and phosphates

In research: Phosphoric acids and phosphates 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 Phosphoric acids and phosphates 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: Phosphoric acids and phosphates is common in secondary-school and first-year university syllabi. It links to neighbouring topics Dietary minerals, Inorganic compounds, Phosphates, so understanding it makes those chapters shorter.
In everyday life: Look for Phosphoric acids and phosphates 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 Phosphoric acids and phosphates in 20 minutes

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

Frequently asked questions

What is Phosphoric acids and phosphates in simple terms?

Why does Phosphoric acids and phosphates 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 Phosphoric acids and phosphates?

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 Phosphoric acids and phosphates.