Laboratory Activity: Teacher Notes

Activity 2: Identifying Products of a Reaction

Major Chemical Concept

The products of a double replacement reaction can be determined experimentally. The amounts of reactants are equimolar.


General or basic student.

Expected Student Background

Students should be familiar with filtration and be able to use a burner safely.


45 min


Read the Safety Considerations in the Student Version.

Materials (For 24 students working in pairs)



Advance Preparation

20 min to assemble the materials.

Pre-Laboratory Discussion

Review the evidence for chemical change and double replacement reactions. Emphasize that the only way we can be sure about the identity of products is to test them. Discuss flame tests if students are unfamiliar with them. The only use of the flame test in this activity is to identify potassium and calcium ions.

Teacher-Student Interaction

During the activity focus students' attention on the difference in properties of the reactants and products. Caution them to observe the flame test before the splint catches on fire. They should compare the colors of the flame tests on the known starting materials and the products.

Anticipated Student Results
Test-Tube Number
Test 1 2 3 4
Flame Violet Red Violet Orange
Acid Bubbles No Rxn No Rxn Bubbles
Answers to Data Analysis and Concept Development

  1. A precipitate is formed.
  2. Observations of reactants:
  3. Potassium carbonate - white solid Calcium chloride - white solid Both dissolved in water Observations of products One substance precipitates and the other dissolves in water, passing through the filter paper.
  4. The precipitate is calcium carbonate; the substance in the filtrate is potassium chloride.

Answers to Implications and Applications

2. K 2 CrO 4 (aq) or Na 2 CrO 4 (aq)
3. Make a solution of a small portion of each solid. Test each solution with a solution of calcium chloride. The one that precipitates is K 2 CO 3 . Alternatively, add dilute hydrochloric acid to both. The one that forms bubbles is K 2 CO 3 .

Post-Laboratory Discussion

The discussion should focus on student answers to Data Analysis and Concept Development questions. The Pictures in the Mind section is particularly important in helping students develop the concept of the particulate nature of matter. These pictures can also be used to explain anomalous results arising from incomplete separations.


  1. Students may plan an investigation to determine the identity of products produced in one of the demonstrations that follow this section.
  2. The use of flame tests as an identification tool may be studied further.

Assessing Laboratory Learning

  1. Extension 1 could serve as an evaluation. Be sure to use reactions involving chemistry that students can reasonably be expected to know.
  2. . Pictures in the Mind of different systems (Example: Demonstration 3) can be used to evaluate whether students have a reasonable concept of what occurs at the molecular level.