Lab07 Chemical Reactions_LabVers2EJM

Lab07 Chemical Reactions_LabVers2EJM - Lab #7 Chemical...

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Lab #7 Chemical Changes Lab (5-03) name____ Erica Murray ___ This laboratory exercise examines the four major types of chemical reactions. Chapter 9 in Kroschwitz, Winokur and Lees textbook , Chemistry a First Course reviews the four major types of chemical reactions. You may will want to review these sections (starting on page 256) to support the new theory presented in this laboratory exercise. Before we examine the four types of chemical reactions, it is important to review the signs that a chemical reaction has occurred . These are various signs or indications that a chemical reaction has occurred. This is a general list and may not include every possibility. SIGNS OF A CHEMICAL REACTION 1. A color change occurs . This indicates that the products are a different color than the reactants. For example; two clear liquids are added together and a dark red material is formed. The color change is due to a new or different substance being made. There may be times in the laboratory where you will see color changes that occur by a dilution process. For example; if you observe a beaker one-half full of diet coke before and after adding an equal amount of distilled water, you will notice a change in the shade of color of the diet coke solution. This is a color change by dilution only. Color change by dilution only, is not by itself a sign of a chemical reaction. 2. A solid is made from the addition of two liquids . If two liquids are added together and a solid occurs, this is a sign a chemical reaction has occurred. The formation of a cloudy solution from two clear solutions is a sign a solid (precipitate )has been made. A precipitate is defined as an insoluble solid which precipitates (settles out) out of a liquid reaction mixture. If such a cloudy mixture is produced, given time it will settle out of the reaction mixture. 3. The disappearance of a solid in a reaction mixture . In some chemical reactions, a solid will be absorbed into a chemical system through the production of a different more soluble pure substance. In some circumstances, a solid can disappear due to its dissolving in water. Table sugar is very soluble in water. The disappearance of sugar when added to pure water is not a chemical reaction. The sugar would only be dissolved and water. It would not have changed into another pure substance. If the water evaporated, the pure sugar solid would reappear. 4. The formation of a gas from liquid or solid reactant(s) . This usually implies a significant amount of gas being formed. Most explosions occur through a chemical reaction. In such reactions a reactant(s) changes into another pure substance(s) resulting in a large volume of gas produced. At room temperature, if 1mL of a solid or liquid is converted to a gas, the resulting gas volume is usually at least 1000 times larger than the starting volume. If you put a sample of tap water in a glass test tube or glass beaker, over a period of time you may witness in the water solution a few small bubbles attached to the glass wall. This is a sign that gases (such as molecular oxygen and
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This note was uploaded on 05/06/2010 for the course CHEM 101 taught by Professor Griffith during the Spring '08 term at Illinois Valley CC.

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Lab07 Chemical Reactions_LabVers2EJM - Lab #7 Chemical...

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