EXPERIMENT 2TYPES OF CHEMICAL REACTIONSOBJECTIVES• Provide examples of the fundamental classes of reactions for macroscopic observations. • Outline the relationship between electrolyte strength and conductivity. • Introduce the use of Excel®as an important software package for chemical analyses. • Discuss the differences between the three symbolic representations of chemical processes: molecular, the ionic, and the net ionic equations. • Reinforce the concept of molarity and provides hands-on experience with using molarity for solution preparation in the laboratory.Introduction There are over 100 known elements and millions of known compounds. Throughout history, chemists have sought to organize the wealth of data and observations that have been recorded for these substances. The most important substance is water. Water is the solvent for all processes involving plant and animal life; our environment depends on aqueous chemical cycles and clean water is essential to life on earth. Reactions that occur in water are numerous but can be classified into four broad categories: precipitation, acid/base, oxidation/reduction and complexation reactions. Understanding these reactions requires understanding of the nature of aqueous solutions in general. • What chemical species are in solution? • Are the chemicals dissolved, ionized, or both? Nature of Aqueous Solutions In order to understand aqueous solutions one must be able to recognize what solutes are dissolved in the solvent water, and whether they dissociate in water creating solvated ions. The term "aqueous" is used to describe solutions in which water is the solvent. One of the simplest methods is to measure the electrical conductivity of an aqueous solution. How well a solution conducts electricity is related to the number of charged particles (solvated ions) that are in solution. The units of conductivity are the inverse of resistivity and are given by the SI units of siemens per meter; S-m–1, but the units are often given in micro-siemens per centimeter, μS-cm. Solutes that dissolve are divided into three qualitative groups: strong electrolytes, weak electrolytes, and nonelectrolytes depending on how much current they allow to flow once dissolved. Strong electrolytes are compounds that completely dissociate in water and include soluble salts and strong acids and bases,. Strong electrolytes yield many charged ions in solution, Weak electrolytes are compounds that only partially dissociate in solution and yielding only a few ions (charge carriers). Weak acids and bases are the most common weak electrolytes, and typically only 1–2% of the molecules dissociate to provide ions. Nonelectrolytes are compounds that dissolve in water but do not dissociate or ionize so therefore furnish no charge carriers in solution. These solutions will not conduct a current.
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