Lab Report: Determination of Partial Molar Properties

Categories: Chemistry


A solution is a homogeneous mixture that is a one-phase system with more than one component. The characteristics of a species in a solution can vary when combined with other species, and these changes can be described as partial molar properties. A partial molar property is a thermodynamic quantity that shows how an extensive property of a solution or mixture changes with variations in the constituents that make up the solution.

The most important partial molar property is the partial molar free energy, which can be mathematically defined as:

∂G/∂ni = μi (Equation 1)

Here, μi represents the chemical potential of component i in the solution.

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The amount of solute in a solvent plays a crucial role in understanding the partial molar characteristics of a solute. In this study, we aim to determine the partial molar volumes of sodium chloride solutions at different concentrations in order to gain insights into their thermodynamic behavior.

Partial molar volumes are defined as:

∂Vi/∂ni = Vi (Equation 2)

Where Vi represents the partial molar volume of component i in the solution. The total change in volume for changes in concentration of the solution can be expressed as:

ΔV = V2 - V1 (Equation 3)

This can be simplified to:

ΔV = V1 - V2 (Equation 4)


Different test solutions were prepared with 2%, 4%, 8%, 12%, and 16% (w/w) sodium chloride. To obtain accurate data, the volume of the pycnometer was determined. The solutions were added to the pycnometer, and their weight was measured to determine the densities. This process was repeated three times for each solution to ensure accuracy.

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Repetition 1

Concentration of NaCl (%) Weight of Vf + NaCl Weight of NaCl
2 142 75.40
4 141.90 79.80
8 127.60 89.70
12 132 89.80
16 145.60 93.40

Repetition 2

Concentration of NaCl (%) Weight of Vf + NaCl Weight of NaCl
2 140.10 76.30
4 140.32 76.50
8 141.50 77.70
12 141.80 78.00
16 147.90 84.10

Repetition 3

Concentration of NaCl (%) Weight of Vf + NaCl Weight of NaCl
2 140.50 77.3
4 141.90 77.7
8 127.60 78.0
12 132.00 78.4
16 145.60 78.8

Data Processing and Interpretation

Determination of Density

The density (d) is determined using the equation:

d = m / V (Equation 5)

Solution Identification (%) Density Repetition 1 (g/cm³) Density Repetition 2 (g/cm³) Density Repetition 3 (g/cm³) Average Density (g/cm³)
2 1.005 1.017 1.030 1.017
4 1.064 1.02 1.036 1.04
8 1.04 1.036 1.196 1.090
12 1.197 1.04 1.045 1.094
16 1.051 1.121 1.245 1.139


Molality (MB) is determined using the expression:

MB = (2 * d) / M₂ (Equation 6)

M (mol/L) Average Density (g/cm³) Molality (MB)
0.3149 1.017 0.299
0.6838 1.040 0.684
1.3675 1.090 1.354
2.0513 1.094 2.106
2.7350 1.139 2.793

Apparent Molar Volume

The apparent molar volume (VB) is determined by the following equation:

VB = (1 / ρ) - (1 / ρA) (Equation 7)

Concentration (mol/L) Average Density ρA (g/cm³) ρ (g/cm³) VB
0.3149 1.017 0.299 0.547 57.5
0.6838 1.040 0.684 0.827 56.2
1.3675 1.090 1.354 1.164 53.6
2.0513 1.094 2.106 1.451 53.4
2.7350 1.139 2.793 1.671 51.3


The experimental data obtained in this study clearly demonstrate that the density of a solution is significantly influenced by its concentration. As more solute is added to a solvent, the composition of particles in the solution changes, leading to an increase in density.

The study also reveals that molality of a solution increases with higher concentrations. The results consistently show a general increase in molality as the concentration of the solution increases.

However, it is noteworthy that sodium chloride solutions exhibit a decrease in partial molar volumes as concentration increases. This finding contradicts previous research by Bhattarai, which suggested an increase in partial molar volume with concentration. This deviation may be attributed to the use of a volumetric flask instead of a pycnometer and the use of a triple beam balance instead of a digitally calibrated analytical balance.

Despite some limitations, this study successfully determined the parameters required to calculate the partial molar volume of the solutions. It emphasizes the importance of using accurate instruments and alternative power sources to ensure high-precision experiments.

In conclusion, this study provides valuable insights into the experimental determination of partial molar properties and their dependence on concentration, even in the face of challenges.


Despite facing electricity challenges that led to the use of triple beam balances instead of digital electrical analytical balances, this experiment successfully determined the partial molar volume of the solutions under study.

Updated: Jan 03, 2024
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Lab Report: Determination of Partial Molar Properties. (2024, Jan 03). Retrieved from

Lab Report: Determination of Partial Molar Properties essay
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