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Chapter 4: 4-5

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Chemical Analysis

Chapter 4: 4-5 Homework

Reading Preparation

Textbook assignment: Read Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 4: Sections 4 and 5.

Study Notes

4.4 Chemical Analysis This section discusses some of the logic and processes chemists use to determine the composition of samples of compounds. Not all methods work in all cases, and experiences is required to chose the best approach. While decomposition methods produce data to help determine the empirical formula, determination of the molecular formula usually requires setting up several different reactions with compounds of known composition, and observing the products.

4.5 Concentrations in Solutions Aqueous solution reactions are affected by the concentration of the solutes and solvents involved. Study the definition of molarity and check the definition of molality as well; know the difference! The two ways of expressing concentration reflect common practices for preparing concentrations in the lab. It is often necessary to prepare solutions of precise molarity for certain chemical reactions, especially those used for analysis or pharmaceuticals. Be able to propose a method of preparation by dilution (this method is the common one, which explains why most chemistry labs have stock solutions of very high —and therefore dangerous — molarities).

Molarity of x with concentration C molarity   =   amount   of   solute   x   ( mol ) volume   of   solution   ( L )

Web Lecture

Read the following weblecture before chat: Chemical Analysis: Measuring Concentrations

Study Activity

Videos for Chapter 4: Chemical Equations

Review the Videos at Thinkwell Video Lessons under STOICHIOMETRY and PHYSICAL PROPERTIES OF SOLUTIONS.

  • A Problem Using the combined concepts of Stoichiometry
  • Characterizing Solutions: Types of Solutions
  • Characterizing Solutions: Molarity and the Mole Fraction
  • Characterizing Solutions: Molality

Play with the Concentration interactive below and see if you can determine

  • How the volume of liquid and the amount of solute are related.
  • How the concentration and solution color are related. (How might you use this to determing solution concentration?)
  • Can you create a solution of precisely 0.5 mol of any one of the combinations of the available solutes? How?
  • How can you change a 0.5 M concentration to a 1.0M concentration precisely?
  • How can you change a 1.0 M concentration to a 0.5M concentration precisely?
  • When is a solution "saturated? What happens if you add more solute at this point?

Chat Preparation Activities

Chapter Quiz

Lab Work


Carry out your experimental plan and post your data to the website for evaluation and discussion.