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3b-double-replacements

3b-double-replacements - CHM151LL CHEMICAL REACTIONS...

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CHM151LL: C HEMICAL R EACTIONS I–D OUBLE R EPLACEMENTS | 1 Classification of Chemical Reactions I– Double Replacements OBJECTIVES: Students who successfully complete this lab exercise and the associated learning activities will: classify chemical compounds, classify reactions, predict the products for some types of chemical reactions, write total ionic and net ionic reaction equations, and predict whether a proposed reaction would occur. DISCUSSION: In this week’s and next week’s lab exercises, your instructor will describe and illustrate the classes of chemical compounds and various types of reactions. Types of Compounds–Strong Electrolytes, Weak Electrolytes, Nonelectrolytes You learned about ionic and covalent compounds in the nomenclature lab. Covalent compounds form when nonmetal elements react to make molecules –structured groups of atoms that are held together by the sharing of electrons. Ionic compounds are held together by the attraction between cations (usually metal) and anions (nonmetal or polyatomic). These differences in the chemical bonding affect the properties of the compounds. For example, electrical conductivity is determined by bonding structure. If any substance conducts electricity, it must contain mobile charge carriers. Covalent compounds ( e.g. water, iodine bromide, sucrose) contain neutral molecules, and even if the molecules are mobile (free to move–in solution or liquid state) the absence of charged particles prevents the passage of electric current. Solid ionic compounds don’t conduct either, for although they contain charged ions, the ions are locked in position. In solution or a molten state, however, the ions become mobile. Movement of the charged ions creates a current, and ionic solutions and melts do conduct. Solutions that have no ions present, called nonelectrolyte solutions, will not conduct electricity. Compounds that easily release many ions into solution will conduct electricity well, and are called strong electrolytes . Some compounds release a relatively small number of ions, and their solutions conduct electricity poorly. We call such compounds weak electrolytes . An electrical circuit with a light bulb and a test solution in series makes a qualitative indicator of conductivity. Your instructor will demonstrate the conductivity of several solutions with such an apparatus. Watch for these typical behaviors: Insoluble ionic compounds are nonelectrolytes.
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