Q: Q1. Give three criteria for a good recrystallization solvent.
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Q: Which of the following solvent systems are not suitable for binary solvent recrystallization?
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Q: Post-lab Questions: does this say about the purity of your solid?
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Q: What properties should ideally be possessed by a recrystallization solvent?
A:
You measured the melting point of the recrystallized product Ttal=142,2-145,5°C. Based on this result, what can you say about your sample?
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- You obtain an Unknown Sample from the Stockroom. You begin testing the solution through the steps outlined in the flowchart of the experiment’s PDF file. You first add HCl and centrifuge your mixture. You observe the formation of a white precipitate in the bottom of the test tube. After pouring off the supernatant liquid, you add hot water to the white precipitate. Upon addition of the hot water, you have some white precipitate still at the bottom of the test tube, and the supernatant liquid is poured off. To this liquid, potassium chromate (K2CrO4) is added. Upon this addition of potassium chromate, you observe no formation of precipitate. Which of the following is a valid conclusion to draw at this point? (Choose one.) Select one: 1. Hg22+ is definitely present. 2. Pb2+ is NOT present. 3. Ag+ is definitely present. 4. Pb2+ is definitely present.You obtain an Unknown Sample from the Stockroom. You begin testing the solution through the steps outlined in the flowchart of the experiment’s PDF file. You first add HCl and centrifuge your mixture. You observe the formation of a white precipitate in the bottom of the test tube. After pouring off the supernatant liquid, you add hot water to the white precipitate. Addition of the hot water dissolves some of the precipitate, but some white precipitate still remains on the bottom of the test tube. You pour off the supernatant liquid, and add ammonia (NH3) to the remaining precipitate. You now observe the formation of a gray-black precipitate. Which of the following is a valid conclusion to draw at this point? Select one: Hg22+ is definitely present. Pb2+ is definitely present. Ag+ could be present, or Hg22+ could be present, or BOTH could be present. Ag+ is definitely presentA student prepared a compound. the melting point of the crude the product was 42 to 48 degree C. after purifying the solid for the first time, the melting point was 47 to 51 degree C. after another purification, the melting point was 50 to 53 degree C. at this stage, can the student confidently say the product has been completely purified? justify your answer
- You obtain an Unknown Sample from the Stockroom. You begin testing the solution through the steps outlined in the flowchart of the experiment’s PDF file. You first add HCl and centrifuge your mixture. You observe the formation of a white precipitate in the bottom of the test tube. After pouring off the supernatant liquid, you add hot water to the white precipitate. Addition of the hot water dissolves some of the precipitate, but some white precipitate still remains on the bottom of the test tube. Which of the following is a valid conclusion to draw at this point? Pb2+ is definitely present. Hg22+ is definitely present. Ag+ could be present, or Hg22+ could be present, or BOTH could be present. Ag+ is definitely presentA student performs a crystallization on an impure sample of biphenyl. The sample weighs 0.5 g and contains about 5% impurity. Based on his knowledge of solubility, the student decides to use benzene as the solvent. After crystallization, the crystals are dried and the nal weight is found to be 0.02 g. Assume that all steps in the crystallization are performed correctly, there are no spills, and the student lost very little solid on any glassware or in any of the transfers. Why is the recovery so low?Using recrystallization techniques, a student attempts to purify 0.50 g of compound H. Based on the solubility of H in the chosen solvent at collection temperature, the maximum percent recovery is 82%. The student obtains 0.396 g of purified crystals. What is their percent recovery? Group of answer choices 41% 64% 79% 82% 97% none of these
- Weigh out accurately 9.99 g of copper(II) sulfate pentahydrate (CuSO4·5H2O) by taring using a clean and dry empty 250-ml beaker. 2. Add tap water to the beaker to reach the 50-mL mark on the side of the beaker. 3. Dissolve all the crystals of CuSO4·5H2O in the water using a clean glass rod for stirring. 4. Then using a glass funnel transfer all the blue solution to a 100-mL volumetric flask. Rinse the beaker with about 10 mL of water and transfer the solution to the volumetric flask. Repeat the rinsing of the beaker with another 10 mL of water and transfer the solution to the volumetric flask. This is called quantitative transfer of the solution. 5. Then add enough water to reach the calibration mark of the volumetric flask. (You will need to use a dropper to add the last few drops of water to ensure the meniscus is on the calibration mark). Close the volumetric flask with a stopper and mix the solution well (so that it is homogeneous). 6. You have now prepared a standard solution (or…5.0 mL of 1-butanol was mixed with 10 mL of HCl. The reaction was put on an ice bath and 4 mL of concentrated sulfuric acid was added. This mixture was refluxed for 45 min and then the product was co-distilled with water using a simple distillation apparatus. Water and the product are immiscible. 1-butanol has a molar mass of 74.12 g/mol, a density of 0.810 g/mL, and a boiling point of 118 C. The product has a molar mass of 92.57 g/mol, a density of 0.880 g/mL, and a boiling point of 78 C. What is the nucleophile in this reaction? What is the role of H2SO4 in this reaction? Calculate the theoretical yield for this reaction. Give your answer in grams. Select the following statements that can be said about the reaction shown.What is another factor that can influence fractional distillation’s success other than the number of theoretical plates?
- 3. Corev was synthesizing a chemical in the laboratory. He used different purification techniques to try to obtain a pure compound. The melting point of the pure compound is 65 degrees. When he tested his compound in the lab the melting point he obtained was 62-68 degrees. Is the product he synthesized pure? 4A company was low on copper metal and decided to use some chemical additives just this once to some copper wiring they were installing in a house. How will this impact the conductivity of the wiring?What are the differences between a simple distillation and steam distillation?2. The goal behind suction filtration is to remove soluble impurities that are on the surface of the crystals. Therefore, why can't you simply use suction filtration instead of recrystallization to purify an impure solid?