chemistry

Salkowski's test

Salkowski's test 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 Salkowski's test rather than just read about it. In short: Salkowski's test, also known simply as Salkowski test, is a qualitative chemical test, that is used in chemistry and biochemistry for detecting a presence of cholesterol and other sterols. This biochemical method got its name after German biochemist Ernst Leopold Salkowski, who is known for development of multiple new chemical tests, that are used for detection of different kinds of molecules (besides cholesterol an…

Key takeaways

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

Reference excerpt

Salkowski's test, also known simply as Salkowski test, is a qualitative chemical test, that is used in chemistry and biochemistry for detecting a presence of cholesterol and other sterols. This biochemical method got its name after German biochemist Ernst Leopold Salkowski, who is known for development of multiple new chemical tests, that are used for detection of different kinds of molecules (besides cholesterol and other sterols also for creatinine, carbon monoxide, glucose and indoles). A solution that has tested positive on the Salkowski's test becomes red and gets yellow glow.

Basic information

Procedure For Salkowski test's procedure one needs a sample, that is to be tested for sterols, as well as chloroform and concentrated sulfuric acid that represent Salkowski's reagent. Usually the solution of chloroform and the sample is prepared first and later treated with concentrated sulfuric (VI) acid. After that the whole solution needs to be shaken well. It is important to use only dried glassware, as dehydration reaction occurs during the test's procedure. A solution that has tested positive on this qualitative chemical test exhibits two distinct layers in a test tube; the upper layer (chloroform) gets blueish red to violet colour, while the layer of sulfuric acid becomes yellow to green, with greenish glow being visible. If a sample does not contain any cholesterol or other sterols, colour of the tested solution remains unchanged and retains its original colour. Salkowski test can also be used to test the presence of indoles (crystalline alkaloids that are a degradation products of proteins, containing tryptophan). In such cases a sample is treated with nitric acid and 2% solution of potassium nitrite, with positive reaction being shown by presence of red colour.

Chemistry of the test Treating a solution of a sample, containing sterols, with chloroform and highly hygroscopic sulfuric acid, leads to a dehydration reaction (two water molecules are removed from two cholesterol molecules) and formation of new double bonds. During the chemical reaction two sterols bind together and bisterol (bisteroid) is formed; bi-cholestadien (double cholestene with two double bonds) in a case of cholesterol. Red colour of a solution is a consequence of bi-sulfonic acid of a bi-cholestadien, which is a product of sulfuric acid sulfonating bi-cholestadien.

References

Salkowski test for cholesterol – Its principle and procedure

Worked examples

Example 1 — a first encounter with Salkowski's test

Start with the simplest possible case. Write down what Salkowski's test 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 Salkowski's test 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 Salkowski's test 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 Salkowski's test

In research: Salkowski's test 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 Salkowski's test 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: Salkowski's test is common in secondary-school and first-year university syllabi. It links to neighbouring topics Biochemistry detection methods, so understanding it makes those chapters shorter.
In everyday life: Look for Salkowski's test 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 Salkowski's test in 20 minutes

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

Frequently asked questions

What is Salkowski's test in simple terms?

Why does Salkowski's test 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 Salkowski's test?

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 Salkowski's test.