Potassium thiocyanate was not added. Test tube turned hot. No deep red color appeared,. Fe 3+ was not present. Step 9: After adding nitric acid, solution remained black. Yellow supernatant (sulfur) were removed after the centrifugation. After adding ammonia, white precipitate formed. Bi 3+ was confirmed. Test tube became very hot to touch. Supernatant was blue, confirmed Cu 2+ . Part B: Step 1: Unknown mixture is number 42. Cations mixture is clear green. Adding HCl produced a white precipitate. Step 2: Clear supernatant solution, no color. White precipitate. Step 3: Adding KI turned the solution a mustard yellow. Pb 2+ was confirmed.
Error: instead of using supernatant from step 2, supernatant from step 1 was used. Step 4: Added 25 drops of 6M NH 3 . White precipitate formed after adding 6M NH 3 , Hg 2 2+ is not present. Supernatant was aqua clear. Step 5: After adding nitric acid and mixing the sample, the precipitate dissolved. No precipitate formed, Ag + is not present. Step 6: pH paper was yellow, green; matched to 0.5 pH. Adding thioacetamide resulted in foam forming on the top of the solution. Used supernatant from step 2 due to error. Step 7: Green, brown precipitate was formed. Warm test tube. Step 8: Adding hydrogen peroxide, did not result in any changes. Clear green substance. Most likely due to error made in step 3. Step 9: Bi 3+ was not confirmed. Supernatant was very dark blue, confirmed Cu 2+ . Most likely due to error made in step 3. ___/ 20 Experimental Part A- In the first part of the experiment, five out of the six cations were identified. Specifically, Ag + ,Pb 2+ ,Hg 2 2+ ,Cu 2+ , and Bi 3+ , were determined to be present in the mixture due to observations made. Cations were identified through the change in color of the solution and the precipitate forming. Each sample was mixed with a substance to trigger chemical reactions. Such chemical reactions either confirmed the presence or the absence of a cation. These concepts were also applied to part B of this lab. However, only two of the three cations were identified, due to an error made when following the procedure. These results, were due to an error. Specifically, instead of using supernatant from step 2 in step 3, supernatant from step 1 was used. This was a major mistake because supernatant 1 that was supposed to be used in step 6 was contaminated. As a result, the third cation was not identified. Part B- Chemical Equations: Pb 2+ (aqs) + 2 KI (aqs) → PbI2 (s) + 2 K + (s) Cu 2+ (aqs) +2NH 3(aqs) →Cu(NH 3 ) 2(aqs)
Known Mixture 4 ml Mixture is a clear blue color. Decantate Group II & III Cu 2+ ,Bi 3+ ,Fe 3+ Supernatant is clear, no color. Decantate & Precipitate dark brown solid brown supernatant Decantate Fe 3+ Pale orange stripes appeared. Precipitate Group I White precipitate was formed Precipitate AgCl, Hg 2 Cl 2 Precipitate White and charcoal (dark grey) precipitate fromed.
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- Spring '14
- Chemistry, Primary color, Decantate