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Unformatted text preview: 35 IONIC REACTIONS in AQUEOUS SOLUTIONS: NET IONIC EQUATIONS Double replacements are among the most common of the simple chemical reactions. Consider the hypothetical reaction: AB + CD AD + CB where AB exists as A + and B- ions in solution and CD exists as C + and D- ions in solution. As the ions come in contact with each other, there are six possible combinations that might conceivably cause a chemical reaction. Two of these combinations are the meeting of ions of like charge; that is, A + with C + and B- with D- . Since particles with like electrical charges repel each other, no reaction will occur. Two other possible combinations are those of the original two compounds; that is A + with B- and C + with D- . This combination would lead to no change. Thus the only possibilities for chemical reaction are the combination of each of the positive ions with the negative ion of the other compound; that is, A + with D- and C + with B- . Example 1: When solutions of sodium chloride and silver(I) nitrate are mixed, the combination of silver(I) cations and chloride anions form silver(I) chloride, which precipitates and settles to the bottom of the container. Note that the states of matter are included: (aq) substance is soluble in water; (s) substance is insoluble in water (solid precipitate) NaCl (aq) + AgNO 3(aq) NaNO 3(aq) + AgCl (s) This combination of chemicals is referred to as a precipitation reaction since an insoluble solid, AgCl, is present as a product. Example 2: When solutions of potassium chloride and sodium nitrate are mixed, the equation for the hypothetical double replacement reaction is: KCl (aq) + NaNO 3(aq) KNO 3 + NaCl But has there been a reaction? Double replacement reactions occur when one of the following is formed as a product of the reaction: a. an insoluble solid (precipitate) - check the solubility table in this lab report. If a solid has formed, this is called a precipitation reaction . b. a gas- for example, CO 2 (from H 2 CO 3 ), SO 2 (from H 2 SO 3 ), or NH 3 (from NH 4 OH). If a gas has formed, this is called a gas forming reaction . c. water from an acid (source of H + ) and a base (source of OH-1 ). If water forms from an acid and a base (along with an ionic "salt"), this is called an acid-base reaction . Using the solubility table (see below) we find both KNO 3 and NaCl are water soluble products. There is no precipitate, gas or water from an acid and base combination. Thus in Example 2, we conclude that even though we can write an equation for a double replacement reaction, no reaction occurs. We simply end up with a solution containing four kinds of ions - Na + , K + , Cl- , and NO 3- . 36 Thus the equation is more properly written: KCl (aq) + NaNO 3(aq) No Reaction Aqueous solutions of sodium chloride and silver(I) nitrate will undergo double replacement reaction to produce a white precipitate of silver(I) chloride and aqueous sodium nitrate. What would happen if we just mixed solid silver(I) nitrate and solid sodium chloride together? silver(I) nitrate and solid sodium chloride together?...
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This note was uploaded on 02/28/2012 for the course CSCE 3510 taught by Professor Unt during the Spring '12 term at North Texas.
- Spring '12