Module 3: Qualitative Analysis of Chemical Reactions

Background

Swimming pools have long been a popular means of recreation, exercise, and physical therapy. Since it is impractical to refill large pools with fresh water on a frequent basis, pool water is regularly treated with chemicals to prevent the growth of harmful bacteria and algae. Proper pool maintenance requires regular additions of various chemical compounds in carefully measured amounts. For example, the relative amount of calcium ion, Ca2+, in the water should be maintained within certain limits to prevent eye irritation and avoid damage to the pool bed and plumbing. To maintain proper calcium levels, calcium cations are added to the water in the form of an ionic compound that also contains anions; thus, it is necessary to know both the relative amount of Ca2+ in the compound and the volume of water in the pool in order to achieve the proper calcium level.

Chemical reactions occur all around us and within our bodies. Recognizing patterns is an important part of chemistry.  By classifying reactions, chemists can predict the identity of products.  This module explores four types of chemical reactions:  chemical solubility and precipitation reactions; acid, base, and neutralization reactions; gas-forming reactions; and oxidation-reduction reactions.  We harness this knowledge and use it in engineering, medical, and industrial applications.

This figure shows a swimming pool that is full of water and surrounded by a concrete patio.
Figure 1. The water in a swimming pool is a complex mixture of substances whose relative amounts must be carefully maintained to ensure the health and comfort of people using the pool. (credit: modification of work by Vic Brincat)

Learning Objectives for Chemical Reactions (Qualitative)

  1. Balance chemical equations by recognizing that in a chemical equation atoms are neither created nor destroyed. Given words or chemical formulas, write the balanced chemical reaction.
  2. Describe why salts dissolve and explain the forces that cause this to occur.
  3. Describe and distinguish the four reaction types and the forces that drive them.  The four types of reactions are:  Precipitation Reactions, Acid/Base Reactions, Gas Forming reactions, and Oxidation-Reduction Reactions
  4. Predict if a reaction will produce a precipitate. Write down the complete and net ionic reactions.
  5. Predict the conductivity of various solutions, including salt, acid, and base solutions.
  6. Define Bronsted acids and bases. Memorize the common strong/weak acids and bases. Describe the characteristics of a neutralization reaction.
  7. Assign oxidation number for elements in a species; identify which element is oxidized (or reduced) in a chemical reaction; identify the oxidizing and reducing agents.

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In the news:  Visit the CDC website to learn more information about acid rain.

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