biology

Hofmann voltameter

Hofmann voltameter is a biology 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 Hofmann voltameter rather than just read about it. In short: A Hofmann voltameter is an apparatus for electrolysing water, invented by August Wilhelm von Hofmann (1818–1892) in 1866. It consists of three joined upright cylinders, usually glass.

Key takeaways

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

Reference excerpt

A Hofmann voltameter is an apparatus for electrolysing water, invented by August Wilhelm von Hofmann (1818–1892) in 1866. It consists of three joined upright cylinders, usually glass. The inner cylinder is open at the top to allow addition of water which contains a low concentration of a compound such as sulfuric acid to improve conductivity and complete the circuit. A platinum electrode is placed inside the bottom of each of the two side cylinders, connected to the positive and negative terminals of a source of electricity. When current is run through Hofmann's voltameter, gaseous oxygen forms at the anode and gaseous hydrogen at the cathode. Each gas displaces water and collects at the top of the two outer tubes. The tubes which collect the product gases are usually graduated, so that the volume of gas can be measured.

Name The name 'voltameter' was coined by Daniell, who shortened Faraday's original name of "volta-electrometer". Hofmann voltameters are no longer used as electrical measuring devices. However, before the invention of the ammeter, voltameters were often used to measure direct current, since current through a voltameter with iron or copper electrodes electroplates the cathode with an amount of metal from the anode directly proportional to the total coulombs of charge transferred (Faraday's law of electrolysis). The modern name is "electrochemical coulometer". Although the correct spelling of Hofmann contains only one 'f', it is often incorrectly depicted as Hoffmann.

Uses The amount of electricity that has passed through the system can then be determined from the volume of gas. Thomas Edison used voltameters as electricity meters. A Hofmann voltameter is often used as a demonstration of stoichiometric principles, as the two-to-one ratio of the volumes of hydrogen and oxygen gas produced by the apparatus illustrates the chemical formula of water, H2O. However, this is only true if oxygen and hydrogen gases are assumed to be diatomic. If hydrogen gas were monatomic and oxygen diatomic, the gas volume ratio would be 4:1. The volumetric composition of water is the ratio by volume of hydrogen to oxygen present. This value is 2:1 experimentally; this value is determined using Hofmann's water voltameter.

See also Timeline of hydrogen technologies Electrolysis of water

References

Illustrations

Worked examples

Example 1 — a first encounter with Hofmann voltameter

Start with the simplest possible case. Write down what Hofmann voltameter claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, 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 Hofmann voltameter 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 Hofmann voltameter 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 Hofmann voltameter

In research: Hofmann voltameter appears in biology 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 Hofmann voltameter 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: Hofmann voltameter is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrolytic cells, Hydrogen production, Hydrogen technologies, so understanding it makes those chapters shorter.
In everyday life: Look for Hofmann voltameter 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 Hofmann voltameter in 20 minutes

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

Frequently asked questions

What is Hofmann voltameter in simple terms?

A Hofmann voltameter is an apparatus for electrolysing water, invented by August Wilhelm von Hofmann (1818–1892) in 1866. It consists of three joined upright cylinders, usually glass.

Why does Hofmann voltameter matter?

Because it connects several biology 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 Hofmann voltameter?

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 Hofmann voltameter.