Chapter4 - 4 Aqueous Reactions and Solution Stoichiometry Aqueous solution A solution in which water is the dissolving medium Solution is a

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1 4. Aqueous Reactions and Solution Stoichiometry • Aqueous solution: A solution in which water is the dissolving medium • Solution is a homogeneous mixture of two or more substances. The substance present in the greatest quantity is usually called solvent. The other substance in the solution are called the solute. 4.1 General Properties of Aqueous Solutions 1. Electrolytic Properties: • Conductor of electricity: a material that contains movable electric charges. • Electrolyte: a substance (e.g. NaCl) whose aqueous solutions contain ions; • Nonelectrolyte: a substance (e.g. Sugar) that does not form ions in solution.
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2 2. Ionic Compounds in Water When NaCl dissolves in water, H 2 O molecules separate, surround, and disperse the ions into liquid. The ionic solid dissociates into its component ions as it dissolves. Ionic compound: those composed of metals and nonmetals (e.g.: NaCl, FeSO 4 ) or compounds containing the ammonium ion (e.g.: NH 4 Cl, (NH 4 ) 2 CO 3 ). Why water is an effective solvent for ionic compounds? – Water is a polar molecule. O atom is rich in electrons and has a partial negative charge ( δ -) while H atom has partial positive charge ( δ +).(water molecule is neutral) – When ionic compound dissolves, the ions are solvated (ions are surrounded by H 2 O). The cations are attracted by the negative end of water and anions are attracted by the positive end of water. – The solvation process helps stabilize the ions in solution and prevents cations and anions from recombining. The ions become dispersed uniformly throughout the solution.
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3 What dissolved species are present in a solution? (be careful with polyatomic ions) • 3. Molecular Compounds in Water • Most molecular compounds are nonelectrolyte. When a molecular compound dissolves in water, the solution usually consists of intact molecules dispersed throughout the solution. • Exception: acids – E.g.: HCl(g) dissolves in water to form hydrochloric acid (HCl(aq)) which consists of H + (aq) and Cl - (aq).
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4. Strong and Weak Electrolytes • Two categories of electrolytes: (according to the extent to which they conduct electricity) – Strong electrolytes: those solutes that exist in solution completely or nearly completely as ions. All soluble ionic compounds and a a few molecular compounds are strong electrolytes. – Weak electrolytes: those solutes that in solution mostly in the form of molecules with only a small fraction in the form of ions. E.g.: acetic acid, formic acid, etc. • Distinguish the extent to which an electrolyte dissolves to whether this electrolyte is strong or weak. E.g.: – Acetic acid (CH 3 COOH) is extremely soluble in water but is a weak electrolyte. – Ba(OH)
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This note was uploaded on 10/06/2008 for the course CHEM 121 taught by Professor Na during the Spring '08 term at John Brown.

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Chapter4 - 4 Aqueous Reactions and Solution Stoichiometry Aqueous solution A solution in which water is the dissolving medium Solution is a

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