摩尔质量的测定——冰点降低.doc

Experiment C25: Molar Mass Determination – Freezing Point Depression摩尔质量的测定——冰点降低(Temperature Sensor)（温度传感器） Concept: the Mole概念：摩尔 Time: 90 m SW Interface: 300, 500 & 700 Macintosh_ file: C25 Molar Mass Windows_ file: C25_MOLA.SWS Adapted from materials from Terri Case, J.I. Case High School, Racine, WI. EQUIPMENT NEEDED所需仪器 ? Science Workshop_ Interface ? temperature sensor温度传感器 ? balance (for measuring mass)天平（用于测量质量） ? beaker,烧杯， 250 mL (for water bath)用于水浴 ? buret clamp滴定管夹 ? heat source (for water bath)加热源（用于水浴） ? ring stand铁环架 ? slit stopper带狭缝的塞子 ? spatula压舌板 ? test tube, Pyrex, 耐热玻璃Pyrex试管， 25 x 150 mm ? apron and safety goggles围裙和防护风镜 CHEMICALS AND CONSUMABLES化学品和消耗品 ? para-dichlorobenzene侧二氯代苯 (PDB) ? “unknown”未知物质 ? water水 ? weighing paper称重纸 PURPOSE目的 The purpose of this laboratory activity is to determine the molar mass of an unknown compound by means of the freezing point depression of p-dichlorobenzene.本实验的目的是通过侧二氯代苯的冰点降低的方法来测定一种未知化合物的摩尔质量。 THEORY原理 Boiling point elevation and freezing point depression are two common examples of colligative properties. Colligative properties depend only upon the concentration of solute particles and not on their size or specific properties. An important use for freezing point depression is the salting of icy roads during the winter in snowy areas. 沸点升高和冰点降低是基于粒子数目的性质的两个常见的例子。基于粒子数目的性质仅仅依赖于溶质粒子的浓度，而与溶质粒子的大小或特性无关。冰点降低的一个重要应用是在多雪地区的冬天往结了冰的路上撒盐。 The freezing point depression,??Tf, of a solvent is given by由下式可得出溶液冰点的降低： ?Tf = kf 2 m where kf is the molal freezing point depression constant for the solvent and m is the molality of the solute particles. The value for kf p-dichlorobenzene is 7.10 C/m.在这里，kf是溶液的摩尔冰点降低常数，m是溶质粒子的摩尔数。侧二氯代苯的kf值为7.10 C/m。 As a pure substance cools in its liquid state the temperature drops at a constant rate until it begins to solidify. While freezing its temperature levels off at a temperature known as its freezing point. Occasionally the temperature drops a little below the actual freezing point