Analytical chemistry ...determination of concentration of copper ions in given sample by u, Schemes and Mind Maps of Analytical Chemistry

Download Analytical chemistry ...determination of concentration of copper ions in given sample by u and more Schemes and Mind Maps Analytical Chemistry in PDF only on Docsity! Student Handout Spectrophotometric Determination of Cu2+ The Problem Branicoda Copper Mine is considering opening up a new mining site. The geologists feel that there are copper-rich ore bodies present at this new site. Samples of these ores were sent to Water Wagon Laboratories to be tested. The ore samples were recently leached with sulfuric acid to bring Cu2+ (copper(II) ion) into solution. Water Wagon Laboratories has been given the challenge of determining the amount of copper present in these solutions. Your Task As a chemical technician at Water Wagon Laboratories, you are responsible for taking the Cu2+ (aq) (aqueous copper(II) solution) and determining the amount of copper present in the solution. To accomplish this task, you must • measure the absorbance of several standard copper solutions using a spectrophotometer. • prepare a linear graph from this data. • measure the absorbance of the ore sample solutions. • use the graph to determine the concentration of copper in the ore sample solutions. Materials Per lab team Spectrophotometer (Spec-20 or Genesys-20) Cuvettes (6 or more) A set of Cu2+ (aqueous copper(II) sulfate solution) standards (5.00 g/L, 4.00 g/L, 3.00 g/L, 2.00 g/L, 1.00 g/L) 1 box lintless paper wipes Safety and Disposal As instructed by your teacher, follow appropriate safety procedures, including the use of personal protective equipment such as goggles and an apron. Copper(II) sulfate pentahydrate is a strong irritant to the skin and mucous membranes. To avoid inhaling its dust, use copper(II) sulfate only where there is adequate ventilation. It can be harmful or fatal if taken internally. If contact with the skin occurs, flush with running water. Wash your hands after use. Follow local ordinances for disposal of copper(II) salts. It is recommended that unused copper(II) sulfate solution be left to evaporate to dryness. Follow any additional disposal procedures as outlined by your instructor. Using a Spectrophotometer A spectrophotometer is used to make absorbance measurements. Light passes into a monochromator (where only the desired wavelength, or a very narrow range of wavelengths, can pass through). The light then passes through the sample, and on to a phototube, where the light energy is converted to an electrical current that is registered on a meter. Absorbance as a function of concentration Notes: There are two types of cuvettes. One type is rectangular and has two smooth sides and two rough sides. When inserting the rectangular cuvettes into the spectrophotometer, make sure that the smooth sides are placed front to back so that the beam shines through the smooth section. The other type of cuvette looks like a regular test tube, but they are not. The tubes have been carefully and precisely made to have a composition that is transparent to light of the visible range and a shape that is a constant 1 cm diameter, perfectly round. Cuvettes must be handled with care, being sure to touch them only near the top, and to wipe off the outside with a piece of lintless paper wipes each time before putting it into the instrument. Cuvettes should be stored in wooden/ plastic test tube racks when not in use to prevent scratching. Procedure 1. Use a disposable pipette to fill a cuvette approximately ¾ full of water. 2. Wipe off the cuvette with a lintless paper wipe. 3. Place the cuvette containing water into the sample compartment and align the lines. This is the reference solution (often called the “blank”). 4. Close the cover and set the absorbance to 0 by moving the lower right hand dial. 5. Remove the cuvette of water. 6. Fill a cuvette approximately ¾ full of one of the standard solutions. It would be