International university – Vietnam national university, HCMC inorganic chemistry laboratory

INTERNATIONAL UNIVERSITY – VIETNAM NATIONAL UNIVERSITY, HCMC INORGANIC CHEMISTRY LABORATORY REPORT EXPERIMENT 1: PREPARATION OF LABORATORY SOLUTIONS GROUP: 2 SECTION: 1 DATE OF SUBMISSION: May 20, 2020 Nguyễn Thị Hồng Nhung BTBCIU18121 Đoàn Ngọc Thảo Vy BTBCIU18085 Đào Thanh Trúc BTBCIU18096 Group members: Instructors: Hoang Le Son Teaching Assistant: Nguyen Thanh Phong ABSTRACT In the first lesson of inorganic chemistry lab, preparing and testing solutions are two basic tasks needed to perform well. Dissolving a solid solute in the solvent or diluting the stock solution (a dilution series by using two techniques that are making parallel dilutions and serial dilutions) is to prepare solution with desired concentration of solute or desired volume. In practical part A, preparation of KMnO4 solution, students apply the formula for making parallel solutions to calculate the volume of known concentration KMnO4 solution and formula for making serial dilutions to find dilution factor. In practical part B, in order to know if the concentration of blue copper sulfate solution is correct, method of spectrophotometry will be used. Spectrometer is set to a wavelength of 700 nm to test by measuring the absorbance of solution in the cuvette. INTRODUCTION One of the most fundamental tasks asked in the laboratory is preparing solutions. Chemists need to accomplish two skills: preparing solutions of known molarity and diluting solutions of known molarity to solutions of new, less concentrated molarities. Molarity is also known as molar concentration and molarity is the number of moles of solute (the material dissolved) per liter of solution. Molarity usually describes exact concentration solutions in which the molecular weight of the solvent is known. Using the analytical balance to weigh solutes and measuring volumes in volumetric flasks are performed. After calculating the mass of solute, taking the grams of solute needed, the solute is put into beaker and technique of dissolving solute into the solvent is carried out. Then, it is transferred into the volume-specific volumetric flasks. Finally, it is completely dissolved in water until the water level reaches the mark. Besides, the method of diluting stock solutions is used in the preparation of small molarity solutions. In general, adding more water to stock solution will obtain the desired solution. When preparing a dilution series, it is very important to know which method is applied (parallel or serial dilution). In addition, filling a cuvette with solution and place it in the spectrometer is to test the accuracy of concentration of this solution. The light goes through the solution and solution absorbs it and finally measures its absorbance which is related to concentration at a given wavelength. Preparing the solution by dissolving a solid solute in the solvent: msolute (g) = Msolute (g/mol) x nsolution (mole/L) x Vsolution (L) msolute: weight of solute needed for the preparation Msolute: formular mass of the solute nsolution: molarity of the solution Vsolution: volume of the solution Making parallel dilutions: C1V1=C2V2 C1 : the concentration of the starting (stock) solution C2 : the desired concentration of final (dilute) solution V1: the volume of starting solution needed to make the dilute V2: the desired volume of final solution Making serial dilutions: V2V1=C1C2=df df: dilution factor V2: the desired volume of the final solution V1: the volume of the more concentrated solution that is mixed with solvent to make a more dilute solution. MATERIALS AND METHOD Materials Materials included beakers, 250 mL volumetric flask, 50 mL volumetric flask, 10 mL volumetric flask, pipette, test tubes, analytical balance, weigh boat, spectrometer, cuvette and some chemicals were potassium permanganate (KMnO4), deionized water (DW) and copper sulphate pentahydrate. Method Part A: Preparation of KMnO4 solution 1. Preparation of 250 mL of 0.01M KMnO4 solution First, calculate and weigh out the amount of KMnO4 needed by using an analytical balance and a small weigh boat. Then transfer it directly to 250 mL beaker. Next, pour 150 mL of DW and stir well until KMnO4 is completely dissolved. Transfer this solution to a 250 mL volumetric flask. If the beaker contain remaining solution, use a few millilitres of DW and transfer it to the volumetric flask. Second, add enough DW to the volumetric flask until the total volume of solution was 250 mL. Finally, cap and invert the volumetric flask three to five times. 2. Preparation of 50 mL of 2mM KMnO4 solution using 0.01M KMnO4 solution First, calculate the volume of 0.01M KMnO4 solution. Then, transfer the required solution into a 50-mL volumetric flask by using an appropriate measuring device. Next, add enough DW until the total volume of solution in this flask is 50 mL. Finally, cap and invert the volumetric flask three to five times. 3. Preparation of several solutions using the parallel dilution from 0.01M KMnO4 solution First, calculate the amount of 0.01M KMnO4 and the amount of DW needed to make 10 mL each of the solutions: 1.0mM KMnO4, 0.6mM KMnO4, 0.4mM KMnO4, 0.2mM KMnO4 and 100μM KMnO4. Then, use tape to label five test tubes. With the first solution, transfer the amount of 0.01M KMnO4 solution into a 10 mL volumetric flask. Add enough DW to the volumetric flask until the total volume of solution was 10 mL and pour into the test tube. After that, clean the 10 mL volumetric flask with DW and do the other experiments in the same way. 4. Prepare several solutions using the serial dilution technique Use the solution of 2mM KMnO4 to make 6 mL of each of the following concentration of KMnO4 included 1.0mM, 0.5mM, 250μM, 125μM, and 62.5μΜ. First, calculate df, V2 and V1. Then, based on the following diagram, the volume and type of liquid needed to place in the tube were written down above each vertical arrow. Moreover, the amount of solution transferred from one tube to the next were noticed below each horizontal arrow. Second, use tape to label each test tube: the first tube with molarity of the stock solution and the others with the final concentrations of the dilutions being prepared. After that, the serial dilutions were performed. A) Place the correct amount of 2mM KMnO4 (V1+V2) into tube 1 and parallel solution was used to make the correct concentration. B) Place the correct amount of solvent into all other tubes. C) Transfer the correct amount of solution (V1) from tube 2 to tube 3 and then thoroughly mix the content of tube 3 with a Vortex mixer. D) Transfer the correct amount of solution (V1) from tube 3 to tube 4 and then thoroughly mix the content of tube 4 with a Vortex mixer. E) Transfer the correct amount of solution (V1) from tube 4 to tube 5 and then thoroughly mix the content of tube 5 with a Vortex mixer. F) The correct amount of solution (V1) was transferred from tube 5 to tube 6 and then thoroughly mix the content of tube 2 with a Vortex mixer. G) Remove the correct amount of solution (V1) from tube 6 and discard it. Finally, place the tubes into a test tube rack in order of decreasing concentration and label the rack “serial solution” . Part B: Preparation/Testing of 0.10M copper sulphate pentahydrate First, calculate and weigh the mass in grams needed to make 50 mL of 0.10M CuSO4.5H2O solution. Then, transfer it carefully into a clean 50 mL volumetric flask. Next, add about two thirds of the volume of DW needed and swirl the flask. Second, fill a cuvette with this solution and place in the spectrometer which is set to a wavelength of 700nm, the concentration is tested to make sure it was correct or not. Finally, the absorbance (A) was recorded because it was directly related to the concentration. RESULT Part A: Preparation of KMnO4 solution 1. Preparation of 250 mL of 0.01M KMnO4 solution Calculation for mass of solid KMnO4: CM = nV n = CM x V n(KMnO4) = 250 x 10-3 x 0.01 = 0.0025 mol m(KMnO4) = n(KMnO4) x 158 = 0.395 g Image 1. The obtained 250 mL KMnO4 0.01M 2. Preparation of 50 mL of 2mM KMnO4 solution using 0.01M KMnO4 solution Calculation for volume of 0.01 M KMnO4 needed to prepare 50 mL of 2mM KMnO4: C1 x V1 = C2 x V2 50 x 2 x 10-3 = 0.01 x V2 V2 = 10 mL Image 2. The obtained 50 mL KMnO4 2mM 3. Preparation of several solutions using the parallel dilution from 0.01M KMnO4 solution Table 1. Calculation for volume of KMnO4 0.01M needed for parallel dilutions technique No Final concentration (mM) Volume of 0.01M KMnO4 (mL) Volume of distilled water (mL) 1 1.0 1 9 2 0.6 0.6 9.4 3 0.4 0.4 9.6 4 0.2 0.2 9.6 5 0.1 0.1 9.9 Image 3. The obtained solutions from parallel dilutions From left to right: 1.0mM, 0.6mM, 0.4mM, 0.2mM, 100μM 4. Prepare several solutions using the serial dilution technique Table 2. Calculation for dilution factor 1 mM (2) 0.5 mM (3) 250 μM (4) 125 μM (5) 62.5 μM (6) df 2 4 8 16 32 V1 3 1.5 0.75 0.375 0.1875 V2 6 6 6 6 6 Image 4. Serial dilutions in order of decreasing concentration of KMnO4 Part B: Preparation/Testing of 0.10M copper sulphate pentahydrate Table 3. Calculation of the mass (g) of CuSO4 needed to prepare 50 mL 0.10 M solution Calculation Result 1. Moles needed = 0.050L × 0.10 mol/L 5×10-3 mol 2. Molar mass of CuSO4.5H2O 250 g/mol 3. Mass in grams needed (1 × 2) = moles × molar mass 1.25 g Image 5. 50 mL 0.10 M solution of 1.25 g of CuSO4.5H2O % Error Absorbance at 700 nm, 0.10 M CuSO4.5H2O, known: 0.77 Absorbance at 700 nm, 0.10 M CuSO4.5H2O, measured: Ameasured = 0.727+0.724+0.7213=0.724 % 𝐸𝑟𝑟𝑜𝑟 = ((Ameasured − Aknown)/ Aknown) × 100% ≈ −5.97 % Table 4. Measurement for the absorbance of distilled water and CuSO4.5H2O solution at 700 nm No Abs K*Abs 1 0.058 0.584 2 0.727 7.279 3 0.724 7.243 4 0.721 7.219 DISCUSSION Part A: Preparation of KMnO4 solution: Preparation of 250mL of 0.01M KMnO4 solution Phenomenon:A 250mL volumetric flask containing a dark purple solution (0.01M KMnO4) Explanation: The KMnO4 0.01M solution is prepared by dissolving a solid KMnO4 in a solvent to obtain a brown-brown solution. The mass of solid KmnO4 is calculated by (m = 0.395), but due to some reasons it is only possible to use 2-decimal scales so that only 0.39g KMnO4 can be used. This leads to a few errors in the data. To ensure weight when transferring all KMnO4 into the vessel, it is necessary to carefully wash the weighing boat and the cup with distilled water several times. Finally, add just enough distilled water to ensure the required volume of solution (250ml). Preparation of 50mL of 2mM KMnO4 solution using 0.01M KMnO4 solution Phenomenon:A 50mL volumetric flask containing a dark purple solution (2mM KMnO4) Explanation: Calculate the required volume of 0.01M KMnO4 using the parallel dilution formula (C1V1 = C2V2). After calculating, take the necessary amount of 0.01M KMnO4 (10ml) into a clean 50mL volumetric flask. Finally add a quantity of distilled water (~ 40mL) to get 50mL of new 2mM KMnO4 solution. Due to the low molar concentration (2mM <0.01m), the final solution has a dark purple color less than 0.01M KMnO4 Preparation of several solutions using the parallel dilution from 0.01M KMnO4 solution Phenomenon: From left to right, the purple color of KMnO4 fades Explain: the required mass of each KMnO4 solution is calculated using a parallel dilution formula. Then, transfer the necessary 0.01M KMnO4 into the test tubes (numbered) and add a suitable amount of distilled water to a volume of 10mL of each tube. Due to errors in the measurement and transfer of materials between instruments, inaccurate data are available. Because of the decreasing trend of molar concentration from left to right (1mM> 0.6mM> 0.4mM> 0.2mM> 0.1mM), the color of the solution also fades in the corresponding direction. Prepare several solutions using serial dilution technique Phenomenon: from left to right purple of the solution fades (diluted ratios 1: 2) Explanation: Dilute the concentration of the solution with the appropriate ratios (1: 2) using the serial dilution technique. This method makes the preparation of low concentrations more easily and properly. The concentrations with small remainder that cannot be measured with devices (62.5μM) will be generated with reliable accuracy. Because the molarity of the solutions from left to right when switching from one solution to another halves , the color of the solution also fades in the corresponding direction. Part B: Preparation/Testing of 0.10M copper (II) sulphate pentahydrate Pour CuSO4.5H2O into about 2/3 of the prepared cuvette and place it on the spectrometer to check the concentration of the solution. After three tests, the absorbance recorded as 0,724 differs significantly from the desired result (0.77). Could be due to errors in the dissolving process of CuSO4.5H2O in the solvent or through surface of light is not clean. According to Bia-Lambert's law, absorbance is linearly correlated with solute concentration and the length of the cuvette [1]. Therefore, the negative error indicates that the solubility concentration of copper (II) sulfate is lower than the solubility concentration of the expected solution. CONCLUSION In order to conduct a successful experiment, it is necessary to perform exactly the steps and the amount of substance involved. The solubility of the substances in the solvent as well as the reaction conditions determine its accuracy. In which parallel and serial dilution techniques have been shown to obtain solutions with very low solubility with high accuracy. In this experiment, the preparation of KMnO4 solution and the copper sulfate pentahydrate concentration of 0.10M were used as examples to practice with the preparation of the solution. Besides, using a spectrometer to measure the concentration of a solution is also essential. Determining and modulating the appropriate concentration has the necessary roles in the preparation of substances in many other solutions. REFERENCES: [1]https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Spectroscopy/Electronic_Spectroscopy/Electronic_Spectroscopy_Basics/The_Beer-Lambert_Law