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Chemical Analysis

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Chemical Analysis

Ever seen someone wee in a pool?

We don't recommend it - besides being impolite, weeing in a pool is injurious to health. The acid in urine reacts with chlorine (used to sanitise swimming pools) and produces toxic gaseous products, which can irritate our lungs and damage our respiratory system.

So, how do you think that scientists studied this chemical reaction? They collected samples of pool water contaminated with urine to understand the risks of weeing in pools. Then, they separated and tested the samples, all so that they could identify the compounds within. Next, they studied the compounds to understand how they react and impact our health. All of this distils down to one field of chemistry: chemical analysis.

  • This article is about chemical analysis.
  • First, we will look into the definition of chemical analysis
  • Then we will have a brief explanation of how chemical analysis is done, and the steps involved in it.
  • Then, we will dive into the types of chemical analysis: qualitative and quantitative analysis.
  • After that, we'll explore different techniques, methods, and tests used in chemical analysis. This includes instrumental methods.
  • Finally, we will understand the importance of chemical analysis.

Definition of chemical analysis

Is it possible to identify the presence of urine in a pool just by looking at it? No! Likewise, we cannot see the toxic products that urine produces on reacting with chlorine. To identify them in the pool water, we use chemical analysis.

Chemical analysis is the process of identifying, separating and quantifying the components of a sample to understand its nature and composition. The branch of chemistry that deals with chemical analysis is called analytical chemistry.

There are different types of chemical analysis, as well as various common techniques and methods. But before we jump into them, let us have a brief look at the steps of chemical analysis.

Steps of chemical analysis

No matter the method or technique used, chemical analysis typically involves the following steps:

  1. Collecting a sample of interest.
  2. Picking an appropriate analytical method to analyse the sample.
  3. Prepping the sample.
  4. Analysing the sample using your chosen method, test, or technique.
  5. Interpreting the results of the analysis. This might involve calculations or further tests.

These steps give us a brief overview of how chemical analysis is done. Each step might have further sub-steps and include unique analytical procedures. The choice of analytical techniques or methods used depends on our sample and the type of chemical analysis we want to carry out. Let's explore the types of chemical analysis now.

Types of chemical analysis: qualitative and quantitative

Chemical analysis is classified into two major types

  • Qualitative chemical analysis.
  • Quantitative chemical analysis.

We'll first have a look into qualitative chemical analysis.

Qualitative chemical analysis

You taste a pizza and might feel it is too hot for your taste. What makes the pizza so spicy? Maybe it is topped with jalapeños, or perhaps pepperoni? These toppings help give the pizza its unique taste and identity.

Chemical Analysis pepperoni pizza slice types of chemical analysis image StudySmarterFig. 1 - a pepperoni pizza slice.Image credit: commons.wikimedia.org

Therefore, to determine why a pizza tastes a certain way, we try to identify what it is topped with. This is a kind of qualitative analysis.

Qualitative chemical analysis is a type of analysis used to identify the substances within a sample and determine whether a particular substance is present or not.

Just like the toppings of a pizza, all the chemical samples have different constituents within them. To determine the constituents of a chemical sample, we use qualitative chemical analysis. It tells us exactly which chemical species the sample is made from, be it different molecules, elements, or compounds.

Quantitative chemical analysis

Let us consider the example of pizza again. We know that the toppings like jalapeños and pepperoni make a pizza taste hot. But how do we know how much pepperoni is added to a pizza? This question is how much of something is answered by quantitative chemical analysis.

Quantitative chemical analysis is a type of analysis used to determine the quantity or the amount of a substance in a sample.

Why might quantitative chemistry be useful? Well, what if you like a little bit of heat on your pizza, but not too much? You'd probably prefer a pizza topped with just a few slices of pepperoni. Knowing exactly how much pepperoni will be in your meal allows you to pick the perfect pizza for you.

In short, qualitative analysis deals with what is present in a sample, while quantitative analysis answers how much of the substance is there.

Chemical analysis: tests, methods, and techniques

For your GCSE exam, you need to know about different techniques, tests, and methods used in chemical analysis. You should be able to compare them as well as discuss why you might choose one approach over another. Here is an introduction to chemical analytical techniques:

  • Testing for pure substances using melting and boiling points.

  • Testing for gases using simple test tube reactions.

  • Testing for ions using reactions that you can carry out in class, such as flame tests, the sodium hydroxide test, and tests for anions.

  • Instrumental analysis, such as chromatography and flame emission spectroscopy.

Chemical Analysis diagram showing flame test results qualititative chemical analysis technique StudySmarterFig. 2 - A diagram showing the colours of flames produced by different ions, an example of qualitative analysis

Instrumental analysis

The tests for gases and the sodium hydroxide test are all simple reactions that you can try out in class. They are quick and convenient to use, but they are qualitative, not quantitative. If we want a quantitative measure of the sample, we have to use certain analytical instruments. They not only identify components of a sample, but also measure their relative amounts. Using analytical instruments in chemical analysis is called (no surprises here) instrumental analysis.

Instrumental methods have certain advantages over test tube reactions. As mentioned above, some are both qualitative and quantitative, whilst most are extremely accurate, sensitive and rapid. In addition, they can work with small samples and are highly versatile.

Here are some examples of instrumental analytical techniques:

  • NMR, IR, UV, x-ray fluorescence, and flame emission spectroscopy are all types of spectroscopic techniques. They use the interactions between electromagnetic (light) waves and particles to help us identify the structure of atoms and molecules.
  • Chromatography works by separating a sample into its components. As well as paper chromatography, which you'll learn about in your GCSE chemistry course, you can find thin-layer chromatography, gas chromatography, gas-liquid chromatography, and many other variations! For example, if you want to separate a mixture of amino acids, you typically use paper or thin layer chromatography.

Check out Instrumental Analysis to learn more about instrumental techniques used in chemical analysis. Additionally, you can explore some of the specific methods we mentioned above at A-level chemistry. Why not explore NMR Spectroscopy or Chromatography to find out further details about the respective subjects?

Examples of chemical analysis

Every household product, from toiletries like shampoo and soap to food products like table salt, sugar, and sauces, is chemically analysed before it reaches you to ensure that it is non-toxic, stable, and safe to use. Given below are a few examples of the fields in which chemical analysis is used and some of its uses that you might encounter.

Field

Uses of chemical analysis

Example

Medicine

  • Diagnosis of diseases

  • Quality control (check) of medicines and drugs

  • RT PCR test to confirm a COVID-19 infection.

  • Glucose screening test to check blood glucose levels.

Food

  • Estimating the nutritional content of different food products

  • Checking for the presence of allergens or toxins

  • Using volumetric titration to determine ingredients such as salt, vitamin C and calcium.

Environmental science

  • Monitoring air pollution

  • Checking for sewage contamination and whether potable water is safe for drinking.

  • The presence of nitrogen dioxide (a common indoor air pollutant) can be detected using chemical analysis.

Sports

  • Analysing the blood and urine samples of sportsmen and women to determine the presence of illegal drugs.

  • Doping tests reveal the presence of banned steroids in the bloodstream of athletes.

Chemical Analysis - Key takeaways

  • Chemical analysis is the process of identifying, separating and quantifying a substance in a sample.

  • There are two types of chemical analysis:

    • Qualitative chemical analysis. This identifies the presence of a substance in a sample.

    • Quantitative chemical analysis. This determines the amount of a substance in a sample.

  • Methods and techniques used in chemical analysis include tests for gases, testing for ions, and instrumental analysis.
  • You find examples of chemical analysis in areas of everyday life such as medicine, the food industry, and sport.

References

  1. Josh Fischman, 'Don't Go in the Water: The Chemistry of Pee in the Pool [Video]'. Scientific American (10/06/2014)

Frequently Asked Questions about Chemical Analysis

Chemical analysis is the process of identifying, separating and quantifying the components of a sample to understand its nature and composition.

Chemical analysis is important to ensure, amongst other reasons:


  • Food is not contaminated and is safe for consumption.
  • The medicines we take are not counterfeit and are of the right standard.
  • The air and the water do not contain any toxic substances.

Chemical analysis is used to:


  • Determine the chemical identity of the constituents of a sample.
  • Separate a sample into its individual components.
  • Measure the amount of the constituents in a sample.


For example, you could use chemical analysis to measure levels of air pollution, screen for allergens in toiletries, or detect toxins in food.

Chemical analysis typically follows these steps:


  • Collecting the sample.
  • Selecting an appropriate analytical technique.
  • Prepping the sample.
  • Analysing the sample using chemical tests and techniques.
  • Obtaining results.
  • Interpretation of results, which often involves chemical calculations.


Qualitative chemical analysis is a type of analysis used to identify the substances within a sample and determine whether a particular substance is present or not.  

Quantitative chemical analysis is a type of analysis used to determine the quantity or the amount of a substance in a sample.

Final Chemical Analysis Quiz

Question

Why do we test for gases?

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Answer

For example:


  • To identify the products of a reaction.
  • To test a hypothesis.

Show question

Question

How do you carry out the test for oxygen?

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Answer

Place a glowing splint inside a test tube full of the gas.


Show question

Question

What is the positive result of the test for oxygen?

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Answer

The glowing splint relights.

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Question

How do you carry out the test for hydrogen?

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Answer

Hold a lit splint over the open end of a test tube full of a gas.

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Question

How do you carry out the test for carbon dioxide?

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Answer

Bubble a gas through limewater.

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Question

How do you carry out the test for chlorine gas?

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Answer

Insert damp blue litmus paper into a test tube filled with gas.

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Question

How do you carry out the test for ammonia?

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Answer

Insert damp red litmus paper into a test tube filled with gas.

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Question

How do you carry out the test for sulfur dioxide?


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Answer

Bubble a gas through acidified potassium dichromate.

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Question

What is the positive result of the test for hydrogen?

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Answer

The lit splint burns with a 'squeaky pop'.

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Question

What is the positive result of the test for carbon dioxide?

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Answer

The clear limewater goes cloudy.

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Question

What is the positive result of the test for chlorine?

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Answer

The damp blue litmus paper bleaches white.

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Question

What is the positive result of the test for ammonia?

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Answer

The damp red litmus paper turns blue.

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Question

What is the positive result of the test for sulfur dioxide?

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Answer

The orange acidified potassium dichromate solution turns green.

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Question

You must carry out the test for _____ in a fume cupboard.

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Answer

NH3

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Question

Give three methods of collecting gas.

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Answer

  1. Over water.
  2. Upward collection.
  3. Downward collection.

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Question

You can use collection over water for ____ gases.

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Answer

Insoluble

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Question

You can use upward collection for gases that are ____.

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Answer

Lighter than air.

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Question

You can use downward collection for gases that are ____.

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Answer

Heavier than air.

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Question

What is the sodium hydroxide test?

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Answer

An analytical technique.

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Question

What do you use the sodium hydroxide test to test for?

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Answer

Positive cations

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Question

Which metal cations CAN'T be identified using the sodium hydroxide test?

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Answer

Group 1 cations

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Question

Outline how you carry out the sodium hydroxide test to identify a metal cation in solution.

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Answer

  1. Pour approximately 10 cm3 of a metal cation solution into a test tube.
  2. Add a few drops of sodium hydroxide solution to the test tube using a pipette.
  3. Observe any changes, noting down the results. 
  4. Gradually add more sodium hydroxide until it is in excess, once again noting any observations. 
  5. Repeat the experiment with different metal cation solutions.

Show question

Question

How does the sodium hydroxide test work?

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Answer

In the sodium hydroxide test, hydroxide ions react with aqueous cations to form an insoluble ionic hydroxide salt, which precipitates out of solution. You can use the colour and solubility of the precipitate to identify the cation present. 

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Question

In the sodium hydroxide test, calcium ions form a ____ precipitate.

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Answer

White

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Question

In the sodium hydroxide test, magnesium ions form a ____ precipitate.

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Answer

White

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Question

In the sodium hydroxide test, aluminium ions form a ____ precipitate.

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Answer

White

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Question

In the sodium hydroxide test, copper(II) ions form a ____ precipitate.

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Answer

Blue

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Question

In the sodium hydroxide test, iron(II) ions form a ____ precipitate.

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Answer

'Dirty' green

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Question

In the sodium hydroxide test, iron(III) ions form a ____ precipitate.

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Answer

Red-brown

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Question

  1. Give three ions that form a white precipitate in the sodium hydroxide test.
  2. Explain how you can distinguish between these ions.

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Answer

  1. Magnesium (Mg2+), calcium (Ca2+), aluminium (Al3+).
  2. Add further sodium hydroxide until it is in excess. The aluminium hydroxide precipitate will dissolve, whilst the calcium and magnesium hydroxide precipitates are insoluble. You can then tell the calcium and magnesium ions apart by carrying out a flame test.

Show question

Question

Give the chemical formula of magnesium hydroxide.

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Answer

Mg(OH)2

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Question

What is the charge of an OH- ion?

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Answer

-1

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Question

What are anions?

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Answer

Negative ions

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Question

Which of the following are anions?

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Answer

Group 1 metal ions

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Question

We test for anions in ____.

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Answer

Giant covalent molecules

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Question

Give the method for testing an unknown solution for carbonate ions.

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Answer

Add a dilute acid.

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Question

Give the method for testing an unknown solution for sulfate ions.

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Answer

Add hydrochloric acid and barium chloride solution.

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Question

Give the method for testing an unknown solution for halide ions.

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Answer

Add dilute nitric acid and silver nitrate solution.

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Question

You carry out a test for carbonate ions. How do you know if you have a positive result?

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Answer

Carbon dioxide gas is given off. You can confirm that this gas is carbon dioxide by bubbling it through clear limewater - the limewater should turn cloudy.

Show question

Question

You carry out a test for sulfate ions. How do you know if you have a positive result?

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Answer

A white precipitate forms.

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Question

You carry out a test for halide ions. How do you know if you have a positive result?

Show answer

Answer

A precipitate forms. Chloride ions give a white precipitate, bromide ions give a cream precipitate, and iodide ions give a yellow precipitate.

Show question

Question

When testing for many anions, you look for precipitates. Which positive anion tests produce a white precipitate?

Show answer

Answer

Test for chloride ions.

Show question

Question

True or false? The test for halide ions uses barium chloride solution.

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Answer

False. The test for halide ions uses dilute nitric acid and silver nitrate solution. The test for sulfates, on the other hand, uses barium chloride solution (alongside hydrochloric acid).

Show question

Question

Why do we add hydrochloric acid before barium chloride solution when testing for sulfates?

Show answer

Answer

The hydrochloric acid removes any aqueous carbonate ions. These also react with barium chloride solution to produce a white precipitate, and so would give a false positive result.

Show question

Question

True or false? You can use hydrochloric acid instead of dilute nitric acid when testing for halides.

Show answer

Answer

False. Hydrochloric acid contains chloride ions, which would react in the test and produce a false positive result.

Show question

Question

True or false? The test for halides is a precipitation reaction.

Show answer

Answer

True

Show question

Question

Give two advantages of tests for anions.

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Answer

For example:


  1. They are cheap.
  2. They are simple to carry out.
  3. They use readily accessible reagents.

Show question

Question

Give two disadvantages of tests for anions.

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Answer

For example:


  1. They are less sensitive and accurate than other analytical techniques.
  2. They can't be used for trace amounts.
  3. They can produce ambiguous results.
  4. They are qualitative, not quantitative.

Show question

Question

How can we determine the concentration of a metal ion within a sample using flame emission spectroscopy?

Show answer

Answer

The intensity of the emitted light determines the concentration of the metal ion. The more intense the light is, the higher the concentration of the metal ion within the solution.

Show question

Question

What is a calibration curve?

Show answer

Answer

A calibration curve is a graph that plots known concentrations of a substance against its spectroscopy reading. Using the graph we can then determine the concentration of a substance when carrying out a flame emission spectroscopy, by collecting the spectroscopy readings. 

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