Pavia, Lampman, Kriz, Engel escale Approach to Organric Laboratory Techniques 5/e this textbook require either of these techniques. If a filtration or decolorizing step is ever required, Technique 11 describes these procedures in detail. Pre-Lab Calculations 1. Calculate how much 95% ethyl alcohol will be required to dissolve 0.3 g of sulfa- nilamide at 78 C. Use the data for the graph in Technique 11, Figure 11.2 to make this calculation. The reason for making this calculation is so that you will know ahead of time the approximate amount of hot solvent you will be adding. 2. Using the volume of solvent calculated in Step 1, calculate how much sulfanilamide will remain dissolved in the mother liquor after the mixture is cooled to 0 C To dissolve the sulfanilamide in the minimum of hot (boiling or almost boiling) solvent, you must keep the mixture at (or near) the boiling point of 95%% ethyl alco- hol during the entire procedure. You wil-likely add more solvent than the amount you calculated because some solvent win evaporate. Ihe amount of solvent is cal- culated only to indicate the approximate amount of solvent required. You should follow the procedure to determine the correct amount.of solvent needed. CEDURE Preparations Weigh 0.30 Page 48 1,042 uc randh this solid to a 10-mL Erlenmeyer lask. Notente cooOneaPurest Tarnacrel To a second Erlenmever flask, a E hp 144 V 697 Crystallization: Purification of Solids TECHNIQUE 11 C (Poor solvent) Very soluble at all temperatures A (Good solvent) Very soluble at elevated temperatures Sparingly soluble at room temperatu re B (Poor solvent) Temperature Figure 11.1 Graph of solubility vs. temperature. at the boiling point of the solvent selected. The as can be seen 250 solubility curve should be steep, in line A of Figure 11.1. A curve with a low slope significant crystalliza- tion when the temperature of the solution was lowered. A solvent in which the material is very soluble at all temperatures (line C) also would not be a suitable crystallization solvent. The basic problem in performing a crystallization is to select a solvent (or mixed solvent) that provides a steep solubility-vs.- temperature curve for the material to be crystallized. A solvent that allows the behav- ior shown in line A is an ideal crystallization sol- vent. It should also be mentioned that solubility 200 (line B) would not cause 150 100 50 60° 80 40° 20° Temperature (C) curves are not always linear, they depicted in Figure 11.1. This figure represents an idealized form of solubility behavior. The solubility for sulfanilamide in 95% ethyl alcohol, shown in Figure 11.2, is typical of many organic compounds and shows what solubility behav- ior might look like for a real substance. This graph is based on the data in the follow- as are Figure 11.2 Solubility of sulfanilamide in 95% ethyl alcohol. curve ing table: Solubility (mg/mL) Temperature 0°C 14 20°C 24 40°C 46 60°C 88 80°C 210 The solubility of organic compounds is a function of the polarities of both the solvent and the solute (dissolved material). A general rule is "Like dissolves like." If the solute is very polar, a very polar solvent is needed to dissolve it; if the solute is nonpolar, a nonpolar solvent is needed. Applications of this rule are discussec extensively in Technique 10, Section 10.2, and in Section 11.5. canned, copied Solubility (mg/mL) Grams soluble-