Explain how rapid crystal growth effects the melting point of the compound. Will it raise or lower the melting point?
The most common method of purifying solid organic compounds is by recrystallization. In this technique, an impure solid compound is dissolved in a solvent and then allowed to slowly crystallize out as the solution cools. As the compound crystallizes from the solution, the molecules of the other compounds dissolved in solution are excluded from the growing crystal lattice, giving a pure solid.
Crystallization of a solid is not the same as precipitation of a solid. In crystallization, there is a slow, selective formation of the crystal framework resulting in a pure compound. In precipitation, there is a rapid formation of a solid from a solution that usually produces an amorphous solid containing many trapped impurities within the solid's crystal framework. For this reason, experimental procedures that produce a solid product by precipitation always include a final recrystallization step to give the pure compound.
The process of recrystallization relies on the property that for most compounds, as the temperature of a solvent increases, the solubility of the compound in that solvent also increases. For example, much more table sugar can be dissolved in very hot water (just below the boiling point) than in water at room temperature. What will happen if a concentrated solution of hot water and sugar is allowed to cool to room temperature? As the temperature of the solution decreases, the solubility of the sugar in the water also decreases, and the sugar molecules will begin to crystallize out of the solution. (This is how rock candy is made.) This is the basic process that goes on in the recrystallization of a solid.
The steps in the recrystallization of a compound are:
Choosing a solvent
The first consideration in purifying a solid by recrystallization is to find a suitable solvent. There are four important properties that you should look for in a good solvent for recrystallization.
majority of chemical processes are reactions that occur in solution. Important industrial processes often utilize solution chemistry. "Life" is the sum of a series of complex processes occurring in solution. Air, tap water, tincture of iodine, beverages, and household ammonia are common examples of solutions.
A solution is a homogenous mixture of substances with variable composition. The substance present in the major proportion is called the solvent, whereas the substance present in the minor proportion is called the solute. It is possible to have solutions composed of several solutes. The process of a solute dissolving in a solute is called dissolution.
Many common mixtures (like concrete) are heterogeneous
Explain how rapid crystal growth effects the melting point of the compound. Will it raise or...
4. Explain how the rate of crystal growth can affect the purity of a recrystallized compound.
Recrystallization: Percent error of melting point and how impurities affect melting point: Please explain both questions below: (Part A) During a recrystallization experiment, the literature melting point of a compound is 105-107 °C. The melting point temperature you obtain from your recrystallized compound is 103-105 °C. Which of the following would be the proper way to set up the percent error of your mp? (a) (104/106)*100 (b) [(106-104)/106] *100 (c) (107/105)*100 (d) [(107-105)/107] *100 (Part B) For a recrystallization experiment...
Which compound has a lower melting point, explain the chemical basis of choice. a. palmitic (a saturated fatty acid) or b. palmitoleic acid (a cis-monounsaturated fatty acid)
Question 14 The melting point of a pure compound is known to be 110-111º. Describe the melting behavior expected if this compound is contaminated with 5% of an impurity. 90-96 111-113 90-91 110-111 5 pts Question 15 You and your lab partner take melting points of the same sample. You observe a melting point of 101-107°C, while your partner observes a value of 110-112°C. Explain how you can get two different values with exactly the same sample. One of the...
why does compound a have a lower melting point? 4) Why does compound a have a lower melting point? (.5 pt) OH
How can you tell that a compound has decomposed on melting and how do impurities affect the melting point of a pure compound?
Question 1 5 pts - What is the purpose of melting point? All the answers To check the purity of solids To check identity of unkown solids To publish for new solids for future characterization Question 2 5 pts How does impurity change melting point value and range? increase-narrowing decrease-narrowing decrease-broadening O increase-broadening Question 3 5 pts What is the reason of an impurity affecting melting point of a solid? Watch Mel. Point Theory video. Not known Obc it weakens...
Question 1 5 pts - What is the purpose of melting point? All the answers To check the purity of solids To check identity of unkown solids To publish for new solids for future characterization Question 2 5 pts How does impurity change melting point value and range? increase-narrowing decrease-narrowing decrease-broadening O increase-broadening Question 3 5 pts What is the reason of an impurity affecting melting point of a solid? Watch Mel. Point Theory video. Not known Obc it weakens...
q3/ one of the most common causes of inaccurate melting points is too rapid heating of the melting point bath . Under these circumstances how will the observed melting point copare to the true melting point ?
Question 14 The melting point of a pure compound is known to be 110-111°. Describe the melting behavior expected if this compound is contaminated with 5% of an impurity. 90-96 111-113 90-91 110-111 5 pts Question 15 You and your lab partner take melting points of the same sample. You observe a melting point of 101-107°C, while your partner observes a value of 110-112°C. Explain how you can get two different values with exactly the same sample. One of the...