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　　Then convert mL to liters:

　　Then divide:

　　Dilution　　Dilution is the process of taking a more concentrated solution and adding water to make it less concentrated. The more concentrated solution before the dilution is performed is known as the stock solution. You can relate the concentration of the stock solution to the concentration of the diluted solution using the equation below:

　　M1V1 = M2V2

　　where M is molarity and V is the volume, in liters, of the solution. Try the following example using this equation. 　　Example　　What volume of 6.0 M sulfuric acid (H2SO4) must be used to prepare 2.0 L of a 0.10 M H2SO4 solution? 　　Explanation　　Just plug the numbers into the formula! Be careful to read closely.

　　M1V1 = M2V2

　　(6.0 M) (V1) = (0.10 M) (2.0 L)

　　V1 = 0.033 L

　　or 33 mL should be measured out and then diluted by adding enough water to make 2.00 L total volume. 　　Mass Percent (Weight Percent)　　The mass percent of a solution is another way of expressing its concentration. Mass percent is found by dividing the mass of the solute by the mass of the solution and multiplying by 100; so a solution of NaOH that is 28% NaOH by mass contains 28 g of NaOH for each 100 g of solution. Here’s the equation:

　　Now try a problem involving the equation:　　Example　　A solution is prepared by mixing 5.00 g ethanol (C2H5OH) with 100.0 g water. Calculate the mass percent of ethanol in this solution.　　Explanation　　Plugging the values we were given into the mass percent equation, we get:

　　Molality (m)

　　The molality of a solution is a measure of the number of moles of solute per kilogram of solvent. Whereas the molarity of a solution is dependent on the volume of the solution, the molality is dependent on the mass of the solvent in the solution. Do not get these confused, and when you see either term on the SAT II Chemistry test, double-check to make sure which one they’re talking about—the words look similar, too! Try an example:　　Example　　A solution is prepared by mixing 80.0 g of sodium hydroxide (NaOH) with 500.0 g of water. Calculate the molality of this solution.　　Explanation　　Convert grams of solute to moles:

　　Convert grams of solvent to kg:

　　Divide:

　　Electrolytes　　Certain solutions are capable of conducting an electric current and these solutions are referred to as electrolytes. Generally speaking, we say that there are three classes of electrolytes (solutions that conduct a current): acids, bases, and salts.Strong electrolytes consist of solutes that dissociate completely in solution. Strong acids, strong bases, and soluble salts are in this category. (We will discuss acids and bases in chapter 6.) Nonelectrolytes are substances that are predominantly covalently bonded, generally will not produce ions in solution, and therefore are considered nonconductors. Weak electrolytes consist of solutes that dissociate only a little in solution. Weak acids, weak bases, and slightly soluble salts are in this category.　　The 美国GREater the de美国GREe of dissociation of the solute, the 美国GREater the conductivity of the solution. Consider two acid solutions that have the same concentration—hydrochloric acid and acetic acid. Hydrochloric acid ionizes completely, while only about 2% of the acetic acid molecules ionize. If a conductivity apparatus were used to test the two solutions, HCl would conduct an electric current to a much 美国GREater de美国GREe because there is more available charge in solution. Below is a figure showing the ionization of barium chloride; as you can see, the Ba+ and Cl- ions are floating free in solution, and this makes barium chloride an electrolyte.
2011-09-20 16:43:00   来源：作文地带    双击单词自动翻译

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