Group 1 Artefacts

Group 1 
Leader: Quek Yong Cai

Identification of Cation:

1) Upon the addition of sodium hydroxide solution, a white precipitate is formed. The white precipitate dissolves when excess sodium hydroxide solution was added.

Possible cations: Al3+, Pb2+, Zn2+

Zn2+ + NaOH -----------> Zn(OH)2 (white precipitate) + Na+

Zn(OH)2 + excess NaOH ------------> Zn(OH)42- (soluble salt)

2) Upon the addition of aqueous ammonia, a white precipitate is formed. The white precipitate dissolves when excess aqueous ammonia was added.

Possible cations: Zn2+

Zn2+ + NH4OH -----------> Zn(OH)2 (white precipitate) + NH4+

Zn(OH)2 + excess NH4OH ------------> Zn(OH)42- (soluble salt)

Therefore, it can be concluded that the cation present is zinc cation.

Identification of Anion:

1) Carbonate Test - Upon the addition of dilute hydrochloric acid, no effervescence was observed, hence the anion is not carbonate ion.

2) Chloride Test - Upon the addition of dilute nitric acid, followed by silver nitrate solution, no white precipitate was observed, hence the anion is not chloride ion.

3) Sulphate Test - Upon the addition of dilute hydrochloric acid, followed by barium chloride solution, no white precipitate was observed, hence the anion is not sulphate ion.

4) Nitrate Test - No gas was liberated after heating the solution with a strong flame, hence the anion is not nitrate ion.

5) Iodide Test - Upon the addition of dilute nitric acid, followed by lead (II) nitrate solution, a yellow precipitate was observed. The yellow precipitate does not dissolve in excess dilute nitric acid.

2 I- + Pb(NO3)2 ---------> PbI2 (yellow ppt) + 2 NO3-

Therefore, it can be concluded that the anion present is iodide ion.

Flowchart of Steps Taken:

Test for Cation in Sample A

Test for Anion in Sample B

Water Analysis: Instructions

Dear Secondary 3E,

Hi! Your Chemistry teachers have prepared two water samples, A and B, for all a special Water Analysis practical. Sample A is a nitrate sample with an unknown cation, and Sample B is a potassium sample with an unknown anion. 

Your class has already been pre-organized into six groups of 6 students. Please download the group list here.

Using what you've learnt in the previous classes on Qualitative Analysis, please come up with a suitable procedure to determine the identities of both the cation and anion in Samples A and B respectively. Specifically, you are to:

1. Upload a video to YouTube that captures your experimental observations (it must be a video of you doing the actual experiment), 
2. Describe and explain the observations by means of relevant chemical equations, 
3. Provide a flowchart of the sequences of tests performed by your group, and 
4. Conclude what the identities of both the cation and anion are.

You may use MindMeister to generate your flowchart, or any other online/offline tool you find useful. Please post and link all artefacts that each of your groups have generated on the class blog, indicating clearly your:

1) Group Number

2) Group Leader

3) Group Artefacts

4) Answers

Please do keep in mind that you only have 50 minutes for this experiment.

At the end of this activity, please comment critically on the artefacts of other groups, specifically:

1) Do you think their answers are correct?
2) Do you think they have described their experimental observations correctly using the right chemical equations?
3) Do you think their experimental techniques were good? Why?
4) Do you think their sequence of chemical tests were logical? Why?
5) Is there anything you would have done differently from them? Why?

Love,
Teacher Doreen