Lab 3 - Solutions and Spectroscopy

Lab 3 - Solutions and Spectroscopy - Lab 3 Solutions and...

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4/15/13 Lab 3 - Solutions and Spectroscopy www.webassign.net/ebooks/wsugencheml1/lab_3/manual.html 1/7 Contents > Lab 3 - Solutions and Spectroscopy Lab 3 - Solutions and Spectroscopy Purpose To determine the concentration of a copper sulfate (CuSO 4 ) solution, and to duplicate its concentration by two methods. Goals To learn how to use a pipet properly. To learn how to dilute a stock solution. To learn how to use a spectrophotometer. To gain practice plotting a calibration curve and use it to determine the concentration of an unknown solution. To learn how to make a solution from a solid reagent. To learn how to make a solution by diluting a stock solution. Introduction A solution is a homogeneous mixture of two or more substances. Simple solutions consist of one solvent and one or more solutes. The solvent is the major liquid component of the mixture in solutions that contain one or more liquids. The most common solutions are aqueous solutions, in which water is the solvent. The concentration of a solute is the ratio of the amount of solute to the amount of solution or solvent. One of the most common ways to report concentration is in units of molarity . Molarity is defined as the number of moles of solute in one liter of solution. It has units of moles/liter (mol/L) and is given the symbol M . For example, if 1.5 moles of sodium chloride is dissolved in enough water to make 1.0 liter of solution, the concentration of sodium chloride is 1.5 M, or 1.5 mol NaCl/L of solution. This would be spoken as "1.5 molar." In order to accurately make solutions of known molarities, we must accurately determine the number of moles of the solute and the volume of the solution. Several pieces of equipment have been developed to measure accurate volumes. These include volumetric flasks, burets, pipets, and graduated cylinders. Other glassware, such as beakers and Erlenmeyer flasks, have volume markings on them, but they are less accurate. Most general chemistry students are
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4/15/13 Lab 3 - Solutions and Spectroscopy www.webassign.net/ebooks/wsugencheml1/lab_3/manual.html 2/7 familiar with the graduated cylinder. It is reasonably accurate and precise (±0.5 to 1 mL depending on its size) and can be used for many measurements. However, greater accuracy and precision is often needed. Several simple devices accurate to 0.01 mL or better are in common use in laboratories. These are: 1 Volumetric flasks . These pear-shaped flasks are designed to contain a volume of liquid or solution which is known to 0.1 mL or better. They have a narrow neck with a single mark. Solvent is added to the mark. 2 Burets . These long, narrow, graduated tubes have a stopcock at the bottom. They are designed to dispense variable amounts of liquid or solution. The volume of solution in the buret is recorded before dispensing the solution and afterward. The difference between the two readings is the volume of liquid dispensed. The volume readings should be to two decimal places. Burets are most often used in titrations.
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Lab 3 - Solutions and Spectroscopy - Lab 3 Solutions and...

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