Lab 4 Report PDF

Preview

Summary

lab 4...

Description

Krenare Tahiri 02/22/2021 Professor Gabriela Smeureanu Lab 4: What is in my sample? “Let’s find the Cations” Introduction In chemistry, qualitative analysis is the process of identifying the number of species in a sample. Confirm the presence or absence of elements. To do this, the mixtures must be separated and then identified. It is possible to identify unknown species by reacting to a known species and observing the reactions. In the cations we have experimented with in this laboratory, some may become solid (precipitate) or others may simply remain dissolved in the solution. A machine used to separate solids and solutions is called a centrifuge. Centrifuge exerts the contents strongly and it separates the contents based on their density. A process called decantation is also used. It is a process that is also used to separate mixtures. After the cations have been successfully identified, we will use the observations we have received to identify the cations in the solution. Data Table Cations

Observations

State

Pb2+

Yellow precipitate that forms Dense liquid after centrifuging KI and supernatant solution confirms presence of Pb2+ 

Hg22+

Dark grey precipitate that forms after centrifuging AgCl and Hg2Cl2 with 6M ammonia confirms presence of Hg22+

Ag+

White precipitate forms after Solid centrifugation of 6M nitric acid to previous supernatant confirms presence of Ag+

Fe3+

Red color solution after adding 3% H202 and 0.1M KSCN to supernatant from step 7 confirms presence of Fe3+

Bi3+

White precipitate adding 6M Solid nitric acid to previous precipitate and 6M NH3 to

Solid

Liquid

the supernatant solution confirms presence of Bi3+  Cu2+

Blue supernatant solution after centrifuging confirms presence of Cu2+ 

Liquid

Focus Questions 1. Cations present in the known mixture include Pb2+, Hg22+, Ag+, Fe3+, Bi3+, and Cu2+. Identification tests that were used involved qualitative analysis and reagents that included HCl, NH3, HNO3, KL, H2O2, C2H5NS, and KSCN. The positive results have been recorded in the observation category of the data table in figure 1. 2. Unknown #9 - Pb2+Bi3+Cu2+ Unknown #10 - Bi3+Ag+Hg2^2+ Post Lab Assessment Questions 1. Decantation- the removal of supernatant in a solution to isolate the precipitate. Centrifugation- the process of forcing the precipitate of a heterogeneous mixture to the bottom of the test tube using centrifugal force. Supernatant- the liquid layer that is separated after centrifugation. Precipitate- the solid substance forced out of a solution after centrifugation. 2. Reagents used to identify the presence of: Ag+: HCl, NH3, HNO3 Hg22+: HCl, NH3 Pb2+: KL 3. Solid precipitates encountered: Yellow- Pb2+ Dark Grey- Hg2^2+ White Precipitate- Ag+ and Bi3+ Blue- Cu2+ Red- Fe3+ 4. The precipitating reagent for the Ag+ (silver) was HCl. The Cl in NaCl can work as a reagent due to its solubility. 5. THe assigned unknown color was #11(white, white, red) and #12(black, blue, red). I can make an inference or educated guess on which ions may be present in the unknown solution based on how they react with certain reagents. 6. I can predict that the silver ions are present due to this case being these ions would be the only thing that could develop a white precipitate.

Unknown Schemes

Balanced Chemical Reactions Sample #9 Yellow, Blue, White (Pb2+, Cu2+, Bi3+) 1. Pb2+  (aq)+KI(aq)---PbI2(s)+ K+(aq) 2. Cu2++H2S→CuS+2H+ CuS+2H+ +No3 →Cu2+  +S+NO2 +H2 O Cu2+  +4NH3 →Cu(NH3 )4 2+ 3. 4Bi3++3H2S→2Bi2S3+6H+  +3S+6NO2+6H2O 4. Bi2S3+12H+ +6NO3→2Bi3+ 5. Bi3++3NH4OH→Bi(OH)3+3NH4+ Sample #10 White, Black, White (Ag+, Hg2^2+, Bi3+)

1. 2Ag++2HCl→2AgCl+H2 AgCl+NH3→Ag(NH3)2+  +Cl Ag(NH3)2+  +4HNO3+CL→AgCl+4NO2+2H2O+NH4+ 2. Hg2++2HCl→Hg2Cl2+H2 Hg2 Cl2 +NH0 →Hg+HgNH2 Cl+HCl 3. 4Bi3++3H2 S→2Bi2 S3+6H+ 4. Bi2S3+12H+ +6NO→2Bi3+  +3S+6NO2+6H2O 5. Bi3+3NH4OH→Bi(OH)3+3NH4+

Conclusions for Part 1 and 2 This lab taught me and my group the importance of qualitative analysis toward identifying cations in a solution. This process makes use of centrifugation, which forces precipitate to the bottom of a homogeneous solution using a centrifuge. The precipitate and supernatant were used to further identify cation testing with help of multiple reagents. During week 1 of this lab, we made a table that showcased the identification steps for the cations in the known solution, color of precipitate/supernatant formed, and reagents used. while using this data table, scheme, and assistance of the professor, me and my group were able to identify which cations were present in the 2 unknown solutions provided, and also figure out the chemical reactions presented from the schemes in the final week. During the final week the class was also brought together to confirm the balance of the chemical equations from the scheme. The purpose and concept of this lab were quite clear because of the lack of an actual lab environment. Me and my group feel as though if in person the hand on experience with the lab would have given this lab a deeper learning experience. Errors Me and my group agreed that the most confusing part of this lab had to be the scheme chart. After conversing with the professor however we were able to properly interpret the scheme in order to properly identify the cations in both the unknown solutions using the colors provided. References Smeureanu, G. & Geggier, S. (2019). General Chemistry Laboratory. New York, NY...