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Exp5 - Experiment 5 CONDUCTOMETRIC TITRATION I Learning...

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5-1 Experiment 5 CONDUCTOMETRIC TITRATION I. Learning Objectives… To introduce conductivity as a means to follow a chemical reaction from soluble reactants to insolubl e products. To apply the Law of Conservation of Matter to balance a chemical equation. II. Background Information The objective of this experiment is to understand the conserved nature of stoichiometry . Stoichiometry is defined as the precise numerical relationship between quantities of reactants and products in a chemical reaction. The Law of Conservation of Matter dictates that the reactants and products in the equation for a chemical reaction must be balanced , meaning the number of atoms of each element must be the same on both sides of the equation. In a chemical reaction substances are changed into other substances by addition to, separation of, or rearrangement of the atoms involved. Atoms can be neither created nor destroyed in chemical reactions (as they can in nuclear reactions). Balancing an equation for a chemical reaction is a fundamental concept necessary in understanding chemistry. In this experiment the Law of Conservation of Matter is used to experimentally determine the quantity of a substance produced from given quantities of reactants. More specifically, known quantities of calcium hydroxide and phosphoric acid are reacted to form calcium phosphate and water. Like many acid-base reactions , calcium hydroxide (base) when combined with an acid reacts to form a salt and water. Calcium hydroxide is a widely used base in industry because it is inexpensive. It is produced by the simple reaction of calcium oxide (lime) with water to yield calcium hydroxide (or slaked lime). CaO (s) + H 2 O (l) Ca(OH) 2 (s) lime slaked lime
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5-2 Consider the balanced reaction below, where calcium hydroxide combines with acetic acid to produce calcium acetate salt and water. Calcium acetate consists of one calcium ion and two acetate ions. Ca(OH) 2 (s) + 2 CH 3 CO 2 H (aq) Ca (CH 3 CO 2 ) 2 (aq) + 2 H 2 O (l) In this equation, two moles of OH - are supplied per mole of Ca(OH) 2 and only one mole of H + ions is supplied per mole of acetic acid. The properly balanced reaction shows that two moles of acetic acid combine with one mole of calcium hydroxide to yield one mole of calcium acetate and two moles of water. Similarly, the unbalanced reaction below shows the combination of calcium hydroxide with phosphoric acid to form calcium phosphate and water. __Ca(OH) 2 (aq) + __ H 3 PO 4 (l) __ Ca x (PO 4 ) y (s) + __ H 2 O (l) Calcium hydroxide is soluble in water at low concentrations. Dissolving the solid in water involves separating each ion from the oppositely charged ions in the solid state. Ca(OH) 2 (aq) Ca +2 (aq) + 2 OH - (aq) The cation s and anions are uniformly dispersed in solution, and the solution is described as an electrolyte . If two electrodes ( conductors of electricity) with a potential difference are placed in the electrolyte solution, the cations ( e.g. , Ca +2 ) migrate to the negative electrode and the anions ( e.g. , OH -
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