Description
In this demonstration, students experience the phenomenon of stoichiometry as they learn that chemical reactants combine in fixed molar ratios according to the coefficients of a balanced equation. Students observe 3 balloons attached to 3 flasks fill with carbon dioxide gas from the reaction of sodium bicarbonate and hydrochloric acid. Each flask has a different proportion of acid to base, resulting in different yields of carbon dioxide gas and unequally filled balloons. A pH indicator provides a qualitative measure of pH for the products in the solutions. Students demonstrate their learning by writing a balanced equation for the reaction in each flask and identifying the limiting and excess reactants from the molar ratios used.
Time Requirement
Total, 30 minutes. Teacher prep, 15 minutes. Demonstration and discussion, 15 minutes.
Digital Resources
Includes 1-year access to digital resources that support 3-dimensional instruction for NGSS. Digital resources may include a teacher manual and student guide, pre-lab activities and setup videos, phenomenon videos, simulations, and post-lab analysis and assessments.
Crosscutting Concepts
Energy and Matter
Connections to Nature of Science: Scientific Knowledge Assumes an Order and Consistency in Natural Systems
Disciplinary Core Ideas
PS1.B: Chemical Reactions
Science and Engineering Practices
Using Mathematics and Computational Thinking
Learning Objectives
- Predict what will happen during each reaction on the basis of prior knowledge.
- Learn how a limiting reactant affects the amount of product in a chemical reaction.
- Illustrate and explain at a molecular level how stoichiometric reactions occur.
Prerequisite Knowledge and Skills
Students should be familiar with atomic, molecular, and formula masses; writing and interpreting a balanced chemical equation; calculating moles from grams and from a given volume of molar concentration; and the pH scale.