O Levels Chemistry Questions – Periodic Table & Group Trends


For the last 2 weeks, i have given several sets of O Level Chemistry Questions on “Tough Question Series” to my Sec 4 students under my coaching. These are not really very tough questions but are more like tricky application questions that test their understanding and concepts.

Let’s check out one of the question on the topic of “Periodic Table & Group Trends”.

Question 1:
You are provided with bromine water, aqueous sodium chloride and aqueous sodium iodide, together with a supply of test tubes. Using these solutions only, describe two experiments to show the relative reactivity of chlorine, bromine and iodine.

For each experiment, describe what you would do and what observation you would make. State how the results of the experiments confirm the relative reactivity and write an equation for any reaction that occurs. [8]

Experiment I:

Experiment II:

Conclusion on relative reactivity:

It came to my awareness that many students are not apt in answering questions on “Describing an experiment….” and make some common errors in their answers.

Below are some of the answers that i have received and the common errors that students tend to make year after year, batch after batch (this is how Up Your Chemistry Grades Now! came about).

Answer by Student A:

Answer by Student B:………

Answer by Student C:

Answers by all 3 students are similar in one way
–> it shows that all 3 of them understand the reactivity of Halogens (Gp VII elements) as it goes down the Group VII.

However, some are:
- not sure about the colour of solutions and elements
- not sure about writing of chemical equations (balanced)
- not sure how to present a “Describe an Experiment…” type of questions.

Please see my suggested answers below:

Experiment I:

Add bromine water to sodium iodide solution.
The colourless sodium iodide solution will turns brownish.
Bromine has displaced iodine from the sodium iodide solution.
This shows that Bromine is more reactive than iodine.

Br2 (aq) + 2NaI(aq) –> 2NaBr(aq) + I2(aq)

Experiment II:

Add Bromine water to sodium chloride solution.
No visible observations.
This shows that bromine is less reative than chlorine.

Br2(aq) + NaCl(aq) –> NO RXNS

Conclusion on relative reactivity:

Reactivity in decreasing order Chlorine > Bromine > Iodine

Hope the above discussion is useful to your learning for O Levels Chemistry.

Before we go off, how about trying out the following question:

Question 2:
Excess bromine is shaken with a mixture of sodium chloride and sodium iodide solutions.
What will the final solution contain?

A. Sodium chloride and sodium bromide
B. Sodium chloride and sodium iodide
C. Sodium iodide and sodium bromide
D. Sodium chloride, sodium bromide and sodium iodide

PS: Let me know your answers and the reasons for choosing it by typing it in the “Leave A Reply” section below.

PPS: If you would like to see more discussion on Periodic Table & Group Trends, Click HERE for more O Level Exam-based questions and answers

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Many people talked about teaching Chemistry, I simply LOVE it. I am a passionate Chemistry Coach based in Singapore, Southeast-Asia and aspire to be one of the most dynamic, powerful and humorous speakers in Asia. My 16+ years of coaching experience has equipped me to understand the true reasons why students are not able to perform well in Chemistry, and allow me to structure my teaching methodology to cater to different levels of learners. If you have found this post useful, please share it with your friends. I would really appreciate it!

8 Responses to O Levels Chemistry Questions – Periodic Table & Group Trends
  1. [...] Chemistry: Secrets of SPA / Chemistry Practicals O Levels Chemistry – Selected Exam Questions O Levels Chemistry – Selected Exam Questions Cont’d O Levels Chemistry Questions – Periodic Ta… Chemistry Phenomenon – Limestone In Action Summary of O Level Chemistry Examinations [...]

  2. Ogundolie Oluwafemi
    April 23, 2009 | 3:53 pm

    Hi sean, u re too much. May the Lord reward u.

    The answer to that question is

    option A : SODIUM BROMIDE & SODIUM CHLORIDE

    Reply

    sean Reply:

    Hi Ogundolie Oluwafemi,

    =) Thanks for the encouraging words!

    Your answer is correct!

    Keep learning!

    To Your Academic Success in Chemistry,
    Sean Chua
    Master Trainer @ SimpleChemConcepts.com
    Author of Up Your Chemistry Grades Now! book

    Reply

  3. jamie
    May 9, 2009 | 9:58 pm

    great questions! still apply to A level

    Reply

    sean Reply:

    Hi jamie,

    I am glad that the Chemistry Tips provided here are still applicable to your A Level Chemistry! =)

    All the best!

    To Your Academic Success in Chemistry,
    Sean Chua
    Master Trainer @ SimpleChemConcepts.com
    Author of Up Your Chemistry Grades Now! book

    Reply

    sean Reply:

    Hi Jamie,

    Just started an A-Level Chemistry Blog specifically for H1 H2 Chemistry students.

    Check out http://www.ALevelH2Chemistry.com.

    Enjoy!

    Reply

  4. stranded
    April 16, 2010 | 5:58 pm

    Is it B?
    Please reply ASAP:)
    THANKS.

    Reply

    sean Reply:

    Answer is A.

    This has to do with Halogen Displacement Reaction in the chapter of Periodic Table.

    Think about it.

    Cheers,
    Sean Chua

    Reply

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