Unit 13 Colour of Metal Salt Solutions & Flame Test

Topic

Colour of metal salts and Flame Test of metals

Curriculum Link

13.3 Properties and uses of metals

Estimated Lesson Time

60 minutes

Introduction

Metals are very common in our daily life. It is interesting to show to students some of the properties of metals they are not aware of. In this activity, we start with asking students to name 1-2 examples of metals they found in their daily life and how they are used. Then we introduce that metals can form salts/compounds with non-metals such as table salt (NaCl). Salts are common in our daily life. Then students are required to complete a table showing the colour of some of the salts formed from metals. Finally they are taught to identify some of the metals by Flame Tests.

Key Question

Could metals be dissolved in liquid? How could we identify metals with their properties?

Learning Objectives

In this activity, the students should be able to

  1. be aware that metals are: hard, usually shiny, with high melting/boiling point, good conductor of heat and electricity;
  2. know that many salts are soluble in water;
  3. make solutions by dissolving salts in water (SP4);
  4. note the colour of some salt solutions (SP1);
  5. understand that the colour of the salt solutions is due to metal ions and that most of these metals (Transition Metals) are located in one group of the Periodic Table (SP5);
  6. identify that the Flame Colour of the following metals such as potassium, sodium, calcium and copper.

Teaching Plan

Task (Time) Brief Description Materials Objectives

Engagement &
Explanation
(15 min)
  • Teacher shows 2-3 different metals and invites students to predict some of the properties of metals (hardness, shininess, high melting/boiling point etc.).
  • Teacher shows some metal salts and demonstrates how to use water to dissolve these salts.
  • Teacher explains the meaning of salts that are formed from metal cations and non-metal anions
   (1)

(2)

Exploration
(15 min)
  • Students then test properties of metals with appropriate apparatus - a hammer (hardness), Bunsen burner (conduction of heat) etc.
  • Students design setup(s) to dissolve the salts given into solutions and identify their colour
  • in a systematic way in compliance with all necessary safety precautions (why using cold water instead of hot water)
 (2) & (3)

Evaluation
(10 min)

Students analyse the set(s) of colour data to

  • identify the colour of the metal ions;
  • tabulate the results and compare the position of the metals in the Periodic Table.
 (4)

Elaboration &
Explanation
(10 min)
  • Students use the Periodic Table provided to locate the position of the coloured metal ions and colourless ions.
  • Teacher generalises that colour ions are common in Transition Metal.
  • Students are asked to search in the web on how colour of Transition metal ions occur - due to d electrons.
Periodic Table

Homework: Internet search		 (5)

Further Exploration
(20 min)

Students are taught how to use Flame Test to identify the flame colour of some metals.
(Students are asked to dissolve 1g of the given metal salt in 95% ethanol. The solution is then transferred to a spray bottle. Then the solution is gently sprayed to a non-luminous Bunsen flame.)

 (6)

Elaboration &
Explanation
(10 min)

Students are asked to search in the web on how colour occurs in Flame Tests - due to outermost shell electrons energy level transitions.

 Homework Internet search  

*Apparatus and materials required: