chemistry

Quantitative analysis (chemistry)

Quantitative analysis (chemistry) 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 Quantitative analysis (chemistry) rather than just read about it. In short: In analytical chemistry, quantitative analysis is the determination of the absolute or relative abundance (often expressed as a concentration) of one, several or all particular substance(s) present in a sample. It relates to the determination of percentage of constituents in any given sample.

Key takeaways

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

Reference excerpt

In analytical chemistry, quantitative analysis is the determination of the absolute or relative abundance (often expressed as a concentration) of one, several or all particular substance(s) present in a sample. It relates to the determination of percentage of constituents in any given sample.

Methods Once the presence of certain substances in a sample is known, the study of their absolute or relative abundance could help in determining specific properties. Knowing the composition of a sample is very important, and several ways have been developed to make it possible, like gravimetric and volumetric analysis. Gravimetric analysis yields more accurate data about the composition of a sample than volumetric analysis but also takes more time to perform in the laboratory. Volumetric analysis, on the other hand, doesn't take that much time and can produce satisfactory results. Volumetric analysis can be simply a titration based in a neutralization reaction but it can also be a precipitation or a complex forming reaction as well as a titration based in a redox reaction. However, each method in quantitative analysis has a general specification, in neutralization reactions, for example, the reaction that occurs is between an acid and a base, which yields a salt and water, hence the name neutralization. In the precipitation reactions the standard solution is in the most cases silver nitrate which is used as a reagent to react with the ions present in the sample and to form a highly insoluble precipitate. Precipitation methods are often called simply as argentometry. In the two other methods the situation is the same. Complex forming titration is a reaction that occurs between metal ions and a standard solution that is in the most cases EDTA (Ethylene Diamine Tetra Acetic acid). In the redox titration that reaction is carried out between an oxidizing agent and a reduction agent. There are some more methods like Liebig method / Duma's method / Kjeldahl's method and Carius method for estimation of organic compounds. For example, quantitative analysis performed by mass spectrometry on biological samples can determine, by the relative abundance ratio of specific proteins, indications of certain diseases, like cancer.

Quantitative vs. qualitative The general expression Qualitative Analysis [...] refers to analyses in which substances are identified or classified on the basis of their chemical or physical properties, such as chemical reactivity, solubility, molecular weight, melting point, radioactivity properties (emission, absorption), mass spectra, nuclear half-life, etc. Quantitative Analysis refers to analyses in which the amount or concentration of an analyte may be determined (estimated) and expressed as a numerical value in appropriate units. Qualitative Analysis may take place with Quantitative Analysis, but Quantitative Analysis requires the identification (qualification) of the analyte for which numerical estimates are given. The term "quantitative analysis" is often used in comparison (or contrast) with "qualitative analysis", which seeks information about the identity or form of substance present. For instance, a chemist might be given an unknown solid sample. They will use "qualitative" techniques (perhaps NMR or IR spectroscopy) to identify the compounds present, and then quantitative techniques to determine the amount of each compound in the sample. Careful procedures for recognizing the presence of different metal ions have been developed, although they have largely been replaced by modern instruments; these are collectively known as qualitative inorganic analysis. Similar tests for identifying organic compounds (by testing for different functional groups) are also known. Many techniques can be used for either qualitative or quantitative measurements. For instance, suppose an indicator solution changes color in the presence of a metal ion. It could be used as a qualitative test: does the indicator solution change color when a drop of sample is added? It could also be used as a quantitative test, by studying the color of the indicator solution with different concentrations of the metal ion. (This would probably be done using ultraviolet-visible spectroscopy.)

Worked examples

Example 1 — a first encounter with Quantitative analysis (chemistry)

Start with the simplest possible case. Write down what Quantitative analysis (chemistry) 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 Quantitative analysis (chemistry) 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 Quantitative analysis (chemistry) 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 Quantitative analysis (chemistry)

In research: Quantitative analysis (chemistry) 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 Quantitative analysis (chemistry) 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: Quantitative analysis (chemistry) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Analytical chemistry, so understanding it makes those chapters shorter.
In everyday life: Look for Quantitative analysis (chemistry) 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Quantitative analysis (chemistry)” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Quantitative analysis (chemistry) in 20 minutes

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

Frequently asked questions

What is Quantitative analysis (chemistry) in simple terms?

Why does Quantitative analysis (chemistry) 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 Quantitative analysis (chemistry)?

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 Quantitative analysis (chemistry).