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Qualitative Analysis – O Level Chemistry

qualitative analysis for O Level Chemistry - how to describe the observations during a chemical test

Qualitative analysis is the process of identifying chemical components present in a sample by doing tests.

In this post, let’s talk about the type of changes we expect to see during qualitative analysis tests.

Examples of observations during qualitative analysis

Let’s use the following as an example. Say we have a sample of solution, and we want to find out what’s present. How would you do so? There are many ways to do so. One method is via adding of chemicals, and looking out for a change. Observing a change is important. If there is no change (i.e. the solution remains the same colour, no gases evolve, etc) we have no idea whether a reaction has taken place, or we have simply just mixed the two chemicals together.

Example of no observable change in qualitative analysis test

qualitative analysis for O Level Chemistry - how to describe the observations during a chemical test when there is no change occurring
No Observable change in the above example. Hence we cannot tell whether there was no reaction, or there was a reaction, but the reaction did not result in an observable change.

Examples of observable changes in qualitative analysis tests

qualitative analysis for O Level Chemistry - how to describe the observations during a chemical test when there is bubbles or effervescence produced
Now we have an observable change. Effervescence observed. This means a reaction has taken place, resulting in gas being produced. We can test the gas and make some conclusions out of it.
qualitative analysis for O Level Chemistry - how to describe the observations during a chemical test when there is a change in colour of the solution
Change in colour of solution. We know a reaction has taken place.
qualitative analysis for O Level Chemistry - how to describe the observations during a chemical test when there is a precipitate being formed
Solid is being produced when two solutions are added. The formation of a precipitate upon adding two solutions indicates a reaction taking place.

In short, we are looking for an observable change during qualitative analysis. The change could be:

  • gas being produced
  • change in colour of the reactants
  • dissolving of a solid
  • producing a solid

Note, during qualitative analysis, you could see more than one of the above change happening at the same time.

Also, do note that if there is no observable change, it doesn’t mean no reaction. It simply means no reaction that produces a change.

Templates to describe observations during qualitative analysis

Here are some templates to describe changes happening during qualitative analysis test.

What happenedTemplate description
Nothing happensNo observable reaction
Solution change colourSolution changed from (initial colour) to (final colour).
Change in colour of solid.Solid changed from (initial colour) to (final colour)

If you see multiple colour change, use something like this:
Solid changed from (initial colour) to (colour) then (colour) and finally to (colour).
Gas produced from a sample containing only solid.(colour), (smell) of gas produced, which (talk about effect on moist litmus paper), and (distinguishing test for gas).
Gas produced from a sample containing liquid.Effervescence of (colour), (smell) of gas produced, which (talk about effect on moist litmus paper), and (distinguishing test for gas).
Solid produced after adding solutions.(colour) precipitate produced.
Solid dissolves in solution.(colour) solid dissolves in solution to give a (colour) solution.
Template to describe your observations during qualitative analysis

Some things to take note when writing observations:

  1. precipitate is formed from solutions.
  2. You only see effervescence (i.e. bubbles) if you start off with liquids. No bubbles will be seen if you only have solids, so don’t use effervescence to describe gases produced when you are heating solids!

More on qualitative analysis

Want a simplified course that will teach you the basics of qualitative analysis and more? Check out our course on qualitative here.

We also have courses on other topics. All these are on-demand courses where students can watch them anytime, anywhere and learn at their own pace.

1. Foundation Topics:

In this course, students will learn the chapters on atomic structure, chemical bonding, elements, molecules and compounds, and also the fundamentals of chemistry – writing equations, and chemical formulae. Check out this course here.

2. Acids, bases and salts, Qualitative Analysis, Metals, Periodic Table, and Ammonia

In this course, students will learn acids, bases and salts, qualitative analysis, metals, periodic table and ammonia. I also share a way of remembering the metals in the reactivity series in this course. You can get this on-demand course here.

3. Mole concept and stochiometry

Questions on mole concept and stoichiometry can be combined with any other chapter. In this course, I will go through with you step- by-step all the concepts you need to know for mole concept and stoichiometry. You can get this on-demand course here.

4. Rate of reaction (reaction kinetics) and heat of reaction (enthalpy change of reaction)

These topics involve applying concepts learnt to scenario-based questions. In our on-demand course on the rate of reaction and heat of reaction, we go through the concepts and how to apply them to questions. You can get this on-demand course here.

5. Redox reactions, electrochemistry and electric cell

Learn redox reactions, and electrolysis and electric cell n this on-demand course here. Most schools cover electrolysis last, so if you want to learn ahead of your school, check out our course here.

6. Organic Chemistry

In O Level Chemistry, students are expected to know the properties, and reactions of alkanes, alkenes, alcohols, carboxylic acids, esters and polymers (addition and condensation polymers). We talk about them in detail in our on-demand course on O Level Organic Chemistry. You can get this on-demand course here.