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7-6 - Solutions and Reactions Chapter 7 ‘ These solutions...

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Unformatted text preview: Solutions and Reactions Chapter 7 . ‘ These solutions, which were made by the laboratory staff, are aqueous - or l" a: water based - solutions. The correct amount of solute was dissolved in ' I: distilled water (the solvent), and the resulting solution was diluted with _.-. water to a known volume to produce a solution of exactly known _'u_ concentration (which the table in your Student Packet identifies). Before ’__' you start exploring chemical reactions, it is necessary to know some of the “.3. chemical properties of the individual solutions. in order to make a solution -~ in the manner described earlier, you must know something about the #3:: solubility of the solute in water. Some general principles about the factors --I. controlling solubility and about the nature of solutions were presented in the Background Chemistry section of this chapter. The next section will -* also consider some general principles of solubility. ‘11. Question: Q1. Let's see how many chemical names you know. Tape the solution chart a. (that you cut out of your Student Packet earlier) into your notebook. - Complete the table by writing in the chemical formula of each solute listed. ""1 (Hint: if you are stuck, you can match the formula on the label of the 4.... microburet to a name in the table.) .3; n" Section B. Solubili and Solutions ”:3. Goal: To examine some of the general principles governing the solubility afvarious solutes 7' in water and other solvents. “'5: { Port 1. Molecular Salutes ‘5; Discussion: The solubility of molecular substances (i.e., substances held together by covalent ....__ bonds) can often be predicted using the "like dissolves like" rule. This means that ' polar molecules dissolve in polar solvents, and nonpolar molecules dissolve in ‘7'- nonpolar solvents. ...._;I Emerimemai Step: 1. At your station are the following solvents: ethanol, pentanol, kerosene and " water. Determine by experiment which are polar and which are nonpolar. __7 ‘ Questions: Q2. Based on your experiments, which of the substances tested are polar, and "' which are nonpolar'? 4-5.: l _ "' Q3. Now take it one step further - rank the 4 substances from most polar to least '5. polar. ""1 Port 2. ionic S olutes Discussion: The solubility of ionic substances (i.e.. substances held together by ionic bonds) is 4-. more difficult to predict. Many ionic substances ("salts") are soluble in water. But .1 many are not. The solubility of ionic solutes depends primarily on the difference " between the stability of the ionic lattice (i.e., how hard is it to pull the ions apart) '._-..- compared to the stability of the solvated (dissolved) ions. Professionals have __ __ cataloged "solubility rules" for ionic substances to make it easier to remember which T" dissolve in water, and which do not. You will have an opportunity to observe and -._: use these generalizations in a later section. ..._ _' 7-13 i ;.l ...
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