CHM 101/102 Laboratory Manual Exchange Reactions General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

CHM 101/102 Laboratory Manual Exchange Reactions Purpose Purpose  To study exchange reactions and learn more about the descriptive chemistry of common chemical compounds. Safety Considerations Safety Considerations  Avoid directly smelling any of the substances in this experiment. Use the wafting technique to detect odors. If one of your unknowns is (NH 4 ) 2 S, work with it in the hood.  Pour all waste materials into the appropriately labeled containers in the hood.

CHM 101/102 Laboratory Manual Exchange Reactions Procedure Procedure  Your lab instructor will give you a list of 10 compounds from which your set of 5 unknowns will be drawn. On the back of this list are the numbers representing your unknowns.  Copy the front and back of the list in your lab book and return the list to your instructor. NaNO 3 KCl Pb(NO 3 ) 2 BaCl 2 KI Na 2 SO 4 K 2 CO 3 AgNO 3 K 2 CrO 4 CuCl 2 Set # frontback

CHM 101/102 Laboratory Manual Exchange Reactions Procedure Procedure  All glassware and plasticware used in this experiment must be clean and rinsed with deionized water to avoid contaminating your unknowns and producing false positive test results.  Label 5 test tubes. Place 3 mL of each of your unknowns in the appropriate test tubes using the pipets supplied with the unknowns. Be sure to return the pipets to their correct containers. approximately 3 mL

CHM 101/102 Laboratory Manual Exchange Reactions Procedure Procedure  Observe and record the color of each of your unknowns. This is important evidence of what is and what is not in your unknown.  Determine the odor of each of your unknowns. This test is performed by wafting vapors from your unknown toward your nose. wafting technique 1 ft  If your unknown contains Na 2 S (rotten egg odor), perform all tests with this substance in the hood.

CHM 101/102 Laboratory Manual Exchange Reactions Procedure Procedure  Test the acidity and basicity of each of your unknowns using red and blue litmus paper.  Perform the litmus tests as shown in these photos. Do not dip litmus paper into the test tube containing your unknown.  Be careful in interpreting the results of litmus tests with colored solutions. acids turn blue litmus red bases turn red litmus blue

CHM 101/102 Laboratory Manual Exchange Reactions Procedure Procedure  Write the numbers of your unknowns along the top and down the side of the 5 x 5 reaction matrix.  Perform each test in a spot plate well and record the colors of any precipitates formed. yellow ppt brown ppt NR NR NR NR white ppt lt. blue ppt white ppt

CHM 101/102 Laboratory Manual Exchange Reactions Procedure Procedure  If your unknown set contains both Cu(NO 3 ) 2 and CuSO 4, you may need to perform an additional test using BaCl 2 to distinguish between them.  Identify each unknown in your set using the data you collected on color, odor, acidity/basicity, and precipitate formation.  Write a balanced chemical equation for each reaction that produced a precipitate. K 2 CrO 4 (aq) + Pb(NO 3 ) 2 (aq) PbCrO 4 (s) + 2 KNO 3 (aq) yellow