Experiment 1.docx - Experiment#1 Qualitative Analysis of...

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Experiment #1 Qualitative Analysis of Cations Student Name: Gabriella Selestiyanta Student Number: 1004627914 Lab Partner: Section Number: 132 Date the experiment was performed: 19 January 2018 Date the lab report was submitted: 26 January 2018 Submitted to George Li Pre-lab Questions Pre-lab Quiz Introduction Experimental Method Collection of Data/Observation Accuracy Discussion Learning Objectives Summary References Experimental Technique Report Presentation Introduction The purpose of this experiment is to carry out a qualitative analysis of some of the commons ions, either Pb 2+ , Cu 2+ , Fe 3+ or Al 3+ , present in a given aqueous solution. This could be done by performing a list of precipitation reactions and confirmatory reaction to both the
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unknown and known solution. The known solution acted as a control solution to give a comparison on which cations were present in the unknown solution. This experiment is often applied to by environmental chemists to get rid of the heavy metals found in wastewaters in order to maintain good quality of the surface waters as well as improving the public’s health 6 . Experimental Method The confirmatory procedure which includes the addition of 6M HNO 3 , water, aluminon reagent, and 6M NH 3 which was supposed to confirm the presence of Al 3+ was skipped due to short amount of time. Moreover, Pasteur pipette was used to transfer the clear liquid above the precipitate to a clean test tube, other than decanting it. The complete method of this experiment can be found in the “CHM 120H5S Chemical Principles 2 2018 Course Manual” on page 18-23. Discussion Solubility Concept In this experiment, the presence of cations was detected by doing a list of precipitation reaction. Precipitation reaction happens when two solutions are reacted to form an insoluble product called a precipitate 7 . Compounds that form precipitates have a very small value of solubility constant, K sp . Most of the time, salts that contain Cl - , NO 3 - , or SO 4 2- is soluble in water 7 . Although, exceptions can be made toward PbCl 2 (which was present in this experiment), AgCl, Hg 2 Cl 2 , BaSO 4 , PbSO 4 , and CaSO 4 , due to the low solubility constant that the compounds have in water. According to the experiment, it was discovered that the unknown solution contained all the cations (Pb 2+ , Cu 2+ , Fe 3+ or Al 3+ ). The discovery of the presence of Pb 2+ was done by primarily reacting it with HCl resulting in the formation of the precipitate PbCl, that had a white color.
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