O chem help. Questions 1,2,4,and 5 please. sink or placing it in the container f

Question

O chem help. Questions 1,2,4,and 5 please.

sink or placing it in the container for aqueous inorganic waste. Dilute the filtrate from the recrystallization with water and wash it down the sink. Questions 1. Describe the factors that could cause you to (b) By how much would this loss lower your obtain an incorrect melting point. percent yield? 2. Suppose the material that you are recrystal!iz- X ing fails to precipitate out of the cold solvent. What would you do to recover the material TABLE 4. 1 Solubility of salicylic acid from the solution? in water at is the white solid that quickly forms when the methyl salicylate is added to the Amount of salicyle wd per 100 t wales Temperature, sodium hydroxide solution? Suppose that you obtain 1.0 g of salicylic acid .3 mL of methyl salicy- 4. from the hydrolysis of 1 late. Calculate your percent yield 10 25 50 75 0.13 023 0.6) (a) Use Table 4.1 and the total estimated volume of solvent that you used for the recrystalliza- tion to calculate the amount of salicylic acid that would remain dissolved in the cold recrystallization solvent if you cooled it to 5. 10°C before filtration.

Explanation / Answer

1) The most likely cause of obtaining an erroneous melting point is the presence of impurities in a sample. Impurities lower the melting point of a solid. This is due to the fact that a solid has a crystalline structure and the presence of impurities disrupts the lattice structure, thereby lowering the energy required to break apart the lattice. Consequently, the melting point decreases due to the presence of impurities.

Another source of error which leads to wrong recording of melting point usually occurs in case of the experimenter. The experimenter may overshoot the melting point, i.e, heat the substance strongly so that the substance melts the temperature overshoots the melting point.

2) At times, a substance may fail to re-crystallize from a cold solution. There should be two immediate points which an experimenter needs to consider. The first point is the solubility of the substance. The substance may have been soluble in water and hence, didn’t precipitate out. In such cases, the solvent needs to be changed. The substance must be dissolved in a solvent which doesn’t solubilize the substance when cold. The solution can be boiled to evaporate water and then the dried substance must be dissolved in a suitable solvent when hot and cooled to crystallize out the substance.

Another way to aid re-crystallization is to scratch the walls of the test tube to start crystallization. A “seed” crystal may be added to start the crystallization process.

Related Questions

Navigate

• Browse (All)
• Browse O
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.