Colligative Properties

Ariana Vellotchka A. Gallardo                         Date Performed: February 5, 2016

Section: B - 2L                                        Date Submitted: February 9,2016

Group Number: 3

Colligative Properties

I. Introduction

        Colligative properties, also known as collective properties, are properties that solely depend on the number of solute particles in solutions and not on the nature of the solute particles. Regardless of whether the solute particles are atoms, ions, or molecules. These colligative properties are vapor pressure lowering, boiling point elevation, freezing-point depression, and osmotic pressure. (Chang, )

        Boiling point elevation is the increase in the boiling point of a solvent caused by the dissolution of a nonvolatile solute (Brown). This could be mathematically expressed by the equation:

Tb - T°b = Kbm

Where:        Tb= boiling point of the solution

        T°b = boiling point of the pure solvent

        Kb = boiling point elevation constant of the solvent

        m = molality of the solution

        Freezing point depression is the freezing point of a solvent caused by the presence of a solute(Brown). This could be mathematically expressed by the equation:

        Tf - T°f = Kfm

Where:

        Tf= boiling point of the solution

        T°f = boiling point of the pure solvent

        Kf = freezing point depression constant of the solvent

        m = molality of the solution

        Naphthalene is a white crystalline solid with the molecular formula of C10H8. Chosen as the chemical mixture to observe the freezing point depression. It has a molecular weight of g/ mole C10H8 and a freezing point depression constant of 6.9°C-Kg/moles solute.

This study aimed to determine the effect of solute concentration to the colligative properties, namely, boiling point and freezing point. Specifically it aimed to:

• compute for the molar mass of an unknown solute using the data gathered on freezing point depression
• determine the relationship between the amount of solute and change in boiling point
• identify the relationship between the amount of solute and change in freezing point

This study was conducted on February 5, 2016 in Room 121, Wing A, at the Institute of Chemistry, University of the Philippines Los Baños, Laguna.

II. Materials

A. Reagents

        10.0 g naphthalene

        500-mL distilled water

        1.00 g unknown solute

        5.00 g assigned solute

B. Apparatus and Equipment

        test tube

        250-mL beater

        test tube holder

        graduated cylinder

        bunsen burner

        iron ring

        iron stand

        wire gauze

        laboratory thermometer

        top loading balance

        stirring rod

        timer

        hot plate

        iron clamp

III. Procedure

        In determining the boiling point elevation of water, there had been five groups of proponents. Each group had 100-mL of distilled water in a 250-mL beaker. Assigned solutes of varying amounts: 0.00 g, 0.50 g, 1.00 g, 1.50 g and 2.00 g had been respectively provided to each group. The mixtures was then heated using the heating plate until the solutes dissolved. The temperature was measured using the laboratory thermometer. Subsequently the continuously stagnant temperature had been recorded and compared with the other groups' temperatures.

        Followed by determining the freezing point depression of naphthalene, where each group had 2.00 g of naphthalene in a test tube. Unknown solutes of varying amounts: 0.00 g, 0.10 g, 0.20 g, 0.30 g, and 0.40 g had been respectively provided to each group. The unknown solute was mixed with the naphthalene then placed in a water bath. The water level of the bath was above the mixture level in the test tube wherein the test tube does not touch the bottom of the beaker. The water bath was then heated using the heating set-up (Figure 1) till the mixture melted. After the mixture completely melted, the heat source was removed. Using the laboratory thermometer and timer the temperature of the mixture was recorded at 15-second intervals along with observing the physical phases. This continued until the mixture finally reached 70°C and solidified.

IV. Data/ Observations

Table 1.1. Determination of boiling points of water and assigned solute

Table 1.2 Freezing Point of Naphthalene

Table 1.3. Gathered data of determination of freezing points of water and assigned solute

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