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Lecture

Experiment 2 Report-CHM120.docx

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Department
Chemistry
Course
CHM120H5
Professor
Judith C Poe
Semester
Winter

Description
Experiment 2: Qualitative Analysis of Cations Lab Section: 0109 th Performed: Wednesday January 30 Submitted: Wednesday February 6 th Submitted to: George Li Pre-lab /20 Purpose /5 Experimental Method /5 Collection of Data /35 Accuracy /10 Summary /3 References /2 Experimental Technique /10 Report Presentation /10 Purpose This lab was a qualitative lab and so the point was to indentify unknown compounds rather than trying to figure out the amounts of different compounds. The purpose of this experiment +2 was to become familiar with some of the characteristic reactions of the four metal ions Pb , Fe , Al , Cu , and to find out which of those metal ions were present in the provided unknown solution. The latter was done by performing the same tests on the given unknown solution and the given known solution concurrently, and then comparing the results. Method The known sample and unknown sample #538 were obtained and poured into test tubes which were labeled accordingly. 5 drops of HCl were added. They were mixed, centrifuged, and liquid and solid components were separated into different labeled test tubes. Water was added to the solids, they were boiled, and mixed, and K2CrO4 was added to them. To the liquids, thioacetamide was added. They were heated, and centrifuged so that the solids and liquids were separated. The liquids were saved for later in marked test tubes. To the solids, water and HNO3 was added, and they were heated. Then NH3 was added and if the solutions turned dark blue, they had Cu(NH3)4+2 ions in them. Acetic acid was added to the blue solutions until the colour faded and they became acidic. K4Fe(CN)6 was added to precipitate Cu2Fe(CN)6. To the saved liquids, HCl was added, and they were centrifuged. The precipitates were thrown away and H2O2 and NaOH were added to the liquids. They were heated and centrifuged for two minutes. Water, H2SO4, and KSCN were added to the precipitates to confirm the presence of Fe(OH)2. To the liquids that were separated by the centrifuge, HNO3 and NH3 were added until a light gelatinous precipitate formed, which was Al(OH)3. To confirm its presence, it was centrifuged, and then HNO3, water, and an aluminum reagent were added so that the solutions became pink. NH3 was added and Al(OH)3 formed again, leaving the solutions colourless. Data Collection Refer to the attached sheets Results and Calculations The following table concisely shows the results of the experiment. It shows which precipitates formed in the unknown solution and what compounds were added in order to produce those precipitates. Table 1: Testing the reactivity of the cations Pb , Fe , Cu , and Al with the anions S , NO , -2 3- -4 - - Fe(CN) ,6OH , and SCN . Cation Thioacetamide HNO 3 K 4e(CN) 6 NaOH KSCN Pb +2 - - - - - +3 +2 Fe - - - Fe(OH) 3 FeSCN (Roan) (Red) +2 Cu CuS Cu(NO ) 3 2 Cu 2e(CN) 6 - (Black) +3 Al - - - Al(OH) 3 (Gelatinous) Conclusions Drawn from the Steps: Step 1: Since PbCl is insoluble, HCL was added to the unknown solution in order to determine +2 whether there were Pb ions in it. This is illustrated by the following equation: Pb aq) + 2Cl (aq)  PbCl (s) 2 +2 Since no white precipitate formed, it was indicated that the unknown solution lacked Pb ions. +2 Step 2: Pb ions precipitate in the form of yellow PbCrO when K Cr44 is adde2: Pb (aq) + K Cr2 (aq4  PbCrO (s) + 2K 4aq) + +2 Since no yellow precipitated, it was confirmed that the unknown solution lacked Pb ions. +2 Step 3: Theoacetamide was added to the unknown solution to precipitate Cu ions as CuS. This would also precipitate the Pb ions as PbS had there been any Pb ions in the unknown. The presence of a fluffy white precipitate floating on the solution indicated that CuS was present. +2 Step 5: NH w3s added to the solution in order to confirm the presence of Cu ions: 2Cu (aq) + 4NH (aq)  Cu (NH ) +2(aq) 3 2 3 4 However, the unknown did not turn blue. Instead its colour changed to a murky orange colour
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