Question
answer of the pre lab assignment..
Thank you
Molar Mass from Freezing-Point Depressiorn 11. A Introduction Solutions have many useful characteristics (Ebbing/Gammon, Cha Among freezing- given quant pter 12). point depression, depend only on the number of solute molecules in a tity of solvent. They do not depend on the nature of the solute. As a con- these are the colligative properties. These properties, which in sequence, colligative properties can be used to determine an unknown molar for a solute (Ebbing/Gammon, Section 12.6). Purpose You will measure the freezing-point depressions that occur with solutions con- taining a solute whose empirical formula is known. Your data and those of the en- tire class will be used to calculate the molar mass of the solute and its molecular formula. Concept of the experiment The apparatus you will use will probably resemble that shown in Figure 11. The solvent will be cyclohexane. The solute will be a substance whose empiri- cal formula is C3H Cl. You will determine the freezing-point depression, AT, This quantity is propor- tional to cm the molal concentration of the solute: The proportionality constant is called the freezing-point-depression constant. It has a value of 20.58 Cym for cyclohexane. You can calculate the molar mass ofa solute from 7, K., themass of the solute, and the mass of the solvent Ebbing/Gammon, Example 12.11) , In order to determine 7, you will measure the freezing point of pure cyclo- hexane and the freezing point of a solution of the solute in cyclohexane. You should use the following methods to obtain these temperatures. FIoURE 1.1 ThermomeserWire stirrer An apparatus suitable for determining the freezing point of a solvent or a solution. Ice and water Liquid whose to be measured 103
Explanation / Answer
Ans 1 :
a) Solution : Solution is a homogenous mixture in which one component is uniformly distributed in the other component.
b) Solute : The solute is the minor component in the solution , which is present in the lesser quantity and uniformly dissolved in solvent.
c) Solvent :The solvent is the major component in the solution , which is present in the greater quantity , which has solute dissolved in it.
d) Collogative property : The colligative properties are the properties of the solution , that do not depend on the identity of the solute , but its concentration.
e) Freezing point depression : It is a colligative property of the solution , which depends on the concentration of solution.
It is given as : depression = kf. m
where kf is the freezing point constant and m is the molality
