How to Memorize the Cations Table in Qualitative Analysis?

When we are studying, not many of us actually have the time to come up creative ways for memorizing. One creative way which is to use acronyms. An example of a common acronym used in secondary school is to remember the seven colours of the rainbow - Roy G. BIV (red, orange, yellow, green, blue, indigo, violet). A shortfall for this method is that not all information can be available as individual words. Hence, creative methods such as acronyms may not work all the time. Also, if there are too many acronyms to remember, can you remember them all?
I prefer a more traditional method, which is breaking down the information to memorize, followed by repetition. I will also be illustrating it using the test for aqueous cations table from the qualitative analysis chapter.

Why break it down?

By breaking it down, I mean breaking up the information you want to memorize into smaller pieces. According to the famous psychology, George A. Miller, our short term memory is limited to seven pieces of information, plus minus two. As a general rule of thumb, try to remember about five pieces of information each time.

If you are interested in finding out the capacity of your short term memory, try the quiz below:

So the first step is to break down the chunk of information you want to memorize into smaller ones, then tackle them one small chunk at a time. It will be good to put related information into one small group at a time, so that it is easier to remember.

Repetition

Repetition --- you use it so often that it becomes a part of you.

For instance, how do you remember 1+ 1= 2 till today? Did you revise that recently?

To remember something for a long period of time, the best way is to use it so often that you do not need to spend time memorizing. However, it is not so easy to reach this stage. You need to recall, and practice very often before it gets internalized.

When I was studying for my examinations, I would first memorize the notes. Subsequently, to make sure I remember them until the examinations, I will recall the information whenever I have the time. I do the recalling most often while waiting for the bus, or when on the bus., If I missed out something, I will look at my notes again, and re- memorize what I have missed out. Also, I will try a few questions from the topic as and when I have small time pockets. By repeating this procedure (and adding more information, since I have to memorize more as the school term goes on), revision for the major exams was a breeze. They are in my head long before the actual exams.

How to memorize the Cations Table in Qualitative Analysis

Next, I'm going to reinforce what I have said earlier in this post with the table below. This cation table is also found in the Qualitative Analysis notes.

Test for aqueous cations

CationsEffect of adding aqueous sodium hydroxideEffect of adding aqueous ammonia

Aluminium (Al³⁺)White ppt.Soluble in excess sodium hydroxide to give a colourless solution.White ppt.Insoluble in excess aqueous ammonia.

Ammonium (NH₄⁺)Not ppt.When heated with sodium hydroxide solution, ammonia gas is evolved.No ppt.

Calcium (Ca²⁺)White ppt.Insoluble in excess sodium hydroxide.No ppt.

Copper (II) (Cu²⁺)Blue ppt.Insoluble in excess sodium hydroxide.Blue ppt.Soluble in excess aqueous ammonia to give a deep blue solution.

Iron (II) (Fe²⁺)Green ppt.Insoluble in excess sodium hydroxide.Green ppt.Insoluble in excess aqueous ammonia.

Iron (III) (Fe³⁺)Reddish- brown ppt.Insoluble in excess sodium hydroxide.Reddish- brown ppt.Insoluble in excess aqueous ammonia.

Lead (II) (Pb²⁺)White ppt.Soluble in excess sodium hydroxide to give a colourless solution.White ppt.Insoluble in excess aqueous ammonia.

Zinc (Zn²⁺)White ppt.Soluble in excess sodium hydroxide to give a colourless solution.White ppt.Soluble in excess ammonia to give a colourless solution.

I break it down the table into five points, and each point has at most five pieces of information:

1. Copper(II) is blue; Iron (II) is green; Iron (III) is reddish brown; the rest form white precipitate and if soluble in excess, becomes colourless solution;
2. Zinc(Zn), aluminium(Al), and lead (Pb) form precipitates that are soluble in excess sodium hydroxide [ or you can remember it as ZAP dissolves in excess NaOH];
3. Copper(II) and zinc ions form precipitates that are soluble in excess aqueous ammonia;
4. Ammonium and calcium form no precipitate when aqueous ammonia is added;
5. Test for ammonium ion is slightly different (you add sodium hydroxide, and heat. Ammonia gas is evolved if ammonium ions are present).

Once you remember these five points, recall them as often as you can (it will generally not take more than 10 minutes!). Also, you should practice questions on this topic often, so as to internalize the information.
Related Posts
- Qualitative analysis (testing for cations, anions and gases)
Questions:
- Quizzes and Tests on Qualitative Analysis - Testing for Cations, Anions and Gases