CHEM 1212L. Lab Manual - Page 22 Freezing Point Depression Objective To use free
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Question
CHEM 1212L. Lab Manual - Page 22 Freezing Point Depression Objective To use freezing point depression to determine the molecular weight of an unknown substance. Introduction the When a nonvolatile solute is dissolved in a particular solvent, some of properties of that solution are affected in a way that depends only on the number of particles introduced to the solvent. The particles can be either ions or m olecules. These properties are called colligative properties. One of the properties affected is the freezing point. The freezing point of a solvent is lowered when a solute is dissolved in that solvent. The freezing point depression, AT, can be expressed mathematically as: where Ti is the freezing point of the pure solvent and Ty is the freezing point of the solution. The freezing point depression can also be expressed in terms of concentration of solute as follows: (Eq. 2) where Kf is the freezing point constant for the solvent and m is the molality of the solution. Molality is defined as: moles of solute kg of solvent (Eq. 3) The solvent you will be using in the lab will be benzophenone, which has a freezing point of 48.1 °C and has a Kf value of 9.80 °C/m Procedure 1. Obtain an unknown and weigh it and its container to the nearest 0.001 grams. 2. Plug the temperature probe into Channel 1 of the computer interface. Follow the instructions given in "Logger Pro Directions" (see Table of Contents for page number) to connect the interface and access the software. The vertical axis should have the temperature scaled from 30°C to 60°C. The horizontal axis has time scaled from O to 10 minutes. If you need to change the vertical scale or horizontalExplanation / Answer
1) Each type of solvent has its respective freezing point constant (Kf), for example, for water Kf = 1.86 ºC / m, in addition to the freezing point of pure water, it is different from that of the substance used in the laboratory (Tcº = 0ºC).
If we want to develop this practice to determine the freezing point of the solution, but with water as a solvent, we must consider the equation:
Tc s = Tcº - Kf * m = 0ºC - 1.86ºC / m * m
and substitute in it, the values ??inherent in the solute.
To realize this difference, we could generate a graph of Concentration vs. Freezing temperature.
2) The electrostatic forces that hold the ions together are strong, it is expensive to separate them. For this reason, it is necessary to provide high temperatures to melt them and their freezing point will be increased.
To realize this difference, we could generate a graph of Concentration vs. Freezing temperature.
1) Each type of solvent has its respective freezing point constant (Kf), for example, for water Kf = 1.86 ºC / m, in addition to the freezing point of pure water, it is different from that of the substance used in the laboratory (Tcº = 0ºC).
If we want to develop this practice to determine the freezing point of the solution, but with water as a solvent, we must consider the equation:
Tc s = Tcº - Kf * m = 0ºC - 1.86ºC / m * m
and substitute in it, the values ??inherent in the solute.
To realize this difference, we could generate a graph of Concentration vs. Freezing temperature.
2) The electrostatic forces that hold the ions together are strong, it is expensive to separate them. For this reason, it is necessary to provide high temperatures to melt them and their freezing point will be increased.
To realize this difference, we could generate a graph of Concentration vs. Freezing temperature.
1) Each type of solvent has its respective freezing point constant (Kf), for example, for water Kf = 1.86 ºC / m, in addition to the freezing point of pure water, it is different from that of the substance used in the laboratory (Tcº = 0ºC).
If we want to develop this practice to determine the freezing point of the solution, but with water as a solvent, we must consider the equation:
Tc s = Tcº - Kf * m = 0ºC - 1.86ºC / m * m
and substitute in it, the values ??inherent in the solute.
To realize this difference, we could generate a graph of Concentration vs. Freezing temperature.
2) The electrostatic forces that hold the ions together are strong, it is expensive to separate them. For this reason, it is necessary to provide high temperatures to melt them and their freezing point will be increased.
To realize this difference, we could generate a graph of Concentration vs. Freezing temperature.