WebLecture: Chemical Analysis: Measuring Concentrations
Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 4: Sections 4-5.
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).
Review the Videos at Thinkwell Video Lessons under STOICHIOMETRY and PHYSICAL PROPERTIES OF SOLUTIONS.
Homework problems: Please visit the Moodle for the current assignment and posting instructions. Do all the homework problems assigned and check the forum for your posting assignment.
Carry out your experimental plan and post your data to the website for evaluation and discussion.
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