My Database Lesson Plan

Science Lesson Plan

Teacher: Arnold Mark Samai

Date: 1^st November 2007

Class: Form 5

Time: 2 Hours

Unit: Qualitative Analysis

Topic: Tests for Cations

References

Chemistry; A Concise Revision Course For CXC by Ann Tindale, Chemistry for CXC – Lambert & Mohammed,

Pre Requisites

Knowledge: students should know - to construct databases and make queries

- to use Microsoft Word to type reports and draw tables

- to use Microsoft Excel to construct tables

Skill

Students should know how to – manipulate basic laboratory apparatus such as test tubes, droppers, reagent bottles

- cations can be present in solutions.

Materials and Resources

For Teacher	For each group student
Computer	15 test tubes and test tube rack
3 test tubes	Test tube holders
Aqueous NaOH	Dil. NaOH solution
Test tube holder	Dil. Aqueous NH3 solution
Test tube rack

With aqueous ammonia solubility varies. Examples include aluminium which precipitates and also forms a white precipitate which is in excess of ammonia solution.

In come reactions when gases are evolved particularly in the case of the presence of the ammonium ion. The evolution of the gas and further analysis can assist in the identification of the cation.

1. Data Base Sheet
2. Type with report
3. Excel to draw table with answers

Basic Principle

Qualitative Analysis involves the identification of cations and anions in aqueous solution. In order to identify cations in solutions we rely on colour changes and their solubility in various reagents.

Objectives

At the end of the lesson students will be able to:

• Explain the underlying principle used to identify cations in solution.

(Classification: Comprehension)

• Perform experiments to identify cations in solution

(Classification: Psychomotor)

• Deduce the cations that are present in known and in known solutions

(Classification: Application)

Process Skills

During this lesson, student will be engaged in:

• Setting up and executing experimental work
• Observing and measuring
• Recording of data and observations
• Interpreting and evaluating data and observations
• Communicating scientific ideas, observations and arguments
• Applying scientific ideas and methods to solve qualitative problems

Students are asked to observe the following procedure.

• Teacher adds:

1. Some KI to a solution containing lead nitrate (intensely yellow precipitate.)
2. Some NaOH to a solution containing ammonium hydroxide and places the stopper of the HCl bottle at the top. (this gives intensely white fumes)
3. Some aqueous Ammonia into a solution containing aluminium nitrate solution. (this gives a white precipitate.)

• Teacher elicits response from the class regarding the observations of coulour changes, evolution of gases and formation of precipitates explaining that these are the basis for identifying cations in solution.

• Teacher instructs students to use the twelve (12) solutions labeled to identify the colours, gases if any, and whether they form precipitates or not with NaOH (aq), aqueous Ammonia, excess NaOH and excess aqueous Ammonia. (see instruction sheet 1 for details).

• Students then asked to construct a group database of the information gathered during the laboratory.

• Teacher and Students engage in group discussion to share findings and clarify anomalies.

• Students are then asked to test unknown substances A, B and C with the reagents provided (see table 2) and use their database to determine the cations present in each solution.

• Teacher and students engage in group discussion of their findings as they justify their conclusion.

• Teacher elicits response from four students in the class to summarize lesson.

Assessment

1. Using examples explain the three factors that are taken into consideration when identifying cations in solution. Your answer is to be typed in Microsoft Word.
2. Using your database fill out the observations and inferences in the table shown below.
3. You are required to construct this table using either Microsoft Word or Excel and Print your answers.

Determination of Cations in Solution

Cations	Addition of NaOH drop wise	Addition of aqueous Ammonia	Addition of excess NaOH	Addition of excess Ammonia
Cr3+	Green (1)	Green (2)	Soluble (3)	Soluble (4)
Fe2+ (5)	Green precipitate	Green precipitate	Insoluble (6)	Insoluble (7)
Cu2+ (8)	Blue (9)	Blue (10)	Blue precipitate insoluble in excess	Blue precipitate insoluble in excess
Al3+, Pb2+, Zn2+ (11)	White precipitate
Mg2+ (12)	White precipitate	White (13)	White precipitate insoluble in excess	Insoluble (14)

Sample	Aqueous NaOH	Aqueous Ammonia	Excess NaOH	Excess Ammonia
A (Zn2+)	White precipitate	White	Soluble	Soluble
B (Cu2+)	Blue	Blue	Insoluble	Insoluble
B (Al3+)	White	White	Soluble	insoluble

There are three factors that are taken into consideration when analyzing cations in solution.

• Colour
• Solubility of precipitate used
• Whether gases are evolved.

Cations form unique electrons in solution which assists in their identification. These include white (Al³⁺, Pb²⁺, Zn²⁺, Pb²⁺), blue (Cu²⁺), green (Fe²⁺), brown (Mn²⁺) and red-brown (Fe3+) just to name a few. The coloured compounds may or may not form precipitates whose solubility differs in aqueous sodium hydroxide and aqueous ammonia solution. Some precipitates dissolve in excess sodium hydroxide such as Zinc, while others form insoluble precipitates for example, Lead.

Continued on page 1.

Table1
Cations	Dropwise NaOH (aq) - Precipitate Evolved	Dropwise NH3 (aq) - Precipitate Evolved	Excess NaOH (aq)	Excess NH3 (aq)
Aluminium	White	White	Soluble	Insoluble
Ammonia	Gas Evolved	No Reaction	Soluble	No Reaction
Barium	Colourless	Colourless	Soluble	Soluble
Calcium	White	No Reaction	Insoluble	Soluble
Chromium	Green	Green	Soluble	Insoluble
Copper (II)	Blue	Blue	Soluble	Soluble
Iron (II)	Green	Green	Insoluble	Insoluble
Iron (III)	Red-Brown	Red-Brown	Insoluble	Insoluble
Lead (II)	White	White	Soluble	Insoluble
Magnesium (II)	White	White	Insoluble	Insoluble
Manganese (II)	Brown	Brown	Insoluble	Insoluble
Zinc (II)	White	White	Soluble	Soluble