A pure substance is a material with constant composition and properties. In order to identify a pure substance, the composition of the substance is determined first. This can be done by doing a physical and chemical analysis of the substance. Once the composition of the substance is known, it can be compared to known standards to determine if it is pure. There are two main types of pure substances: elements and compounds. Vinegar is an example of a compound, as it is made up of water and acetic acid (Singh, 2020). Color, odor, and solubility are qualitative determinations, while boiling point and density are quantitative (numerical) measurements. While the ratio of these two substances can vary, the chemical makeup of vinegar remains the same. As a result, vinegar can be used as a reliable indicator of compound purity.
In this lab, the physical properties of ethanol (vinegar) have been determined and used to verify the purity of the vinegar sample. Some physical properties determined for the sample include color, odor, solubility in water, solubility in ethanol, density, and boiling point. The experimental values obtained for the substance have been compared to the standard physical properties of the substance to evaluate its purity.
Procedure
To determine the density of the unknown liquid A, 10 ml of the liquid was weighed in a clean and dry graduated cylinder. The mass of the empty graduated cylinder was determined first and recorded. The mass of the graduated cylinder with 6 ml of the liquid was weighed and recorded in the data table. The procedure was repeated twice to make three trials. The order of the unknown liquid was determined using the wafting technique while its color was observed and recorded in the results. Additionally, the liquid was dissolved in water and ethanol to determine its solubility properties in the two solvents.
Finally, a shallow dish, a candy thermometer, and ice water were used to determine the boiling point of the unknown liquid. The dish was filled with ethanol and placed on a heat-resistant surface. The candy thermometer was placed in the liquid so that the bulb was submerged, but the stem was not touching the bottom or sides of the dish. The heat turned on, and the liquid was allowed to boil. When the unknown liquid boiled, the heat was turned off, and the dish was removed from the burner. The dish was immediately placed in a bowl of ice water to stop the boiling process; the temperature value on the candy thermometer was recorded as the boiling point of the liquid. The procedure was repeated twice to help determine the average boiling point of the liquid.
Results
Density Calculation:
Mass of the liquid= Mass of graduated cylinder and liquid – Mass of the graduated cylinder
The density of the liquid= Mass of the liquid/ Volume of the liquid
Table 1: Calculation of density of the unknown liquid.
| Parameter | Trial 1 | Trial 2 | Trial 3 |
| Mass of the graduated cylinder | 27.160 g | 27.213 g | 27.242 g |
| Mass of the graduated cylinder + unknown liquid | 31.908 g | 31.920 g | 31.903 g |
| Mass of the unknown liquid | 4.748 g | 4.707 g | 4.661 g |
| The volume of the liquid sample | 6 ml | 6 ml | 6 ml |
| Calculated density | 0.7913 | 0.7845 | 0.6935 |
Table 2: determination of the boiling point of the unknown liquid
| Trials | Determined B.P (0C) |
| 1 | 78.17 |
| 2 | 78.18 |
| 3 | 78.39 |
Table 3: Physical properties of the unknown liquid.
| Odor | Color | Average boiling point | Average density | Solubility in water | Solubility in Ethanol |
| Smells like nail polish | Colorless | 78.25 0C | 0.7569 g/ml | Very soluble | Very soluble |
Discussion and Conclusion
The unknown liquid’s physical properties (odor, color, density, boiling point, and solubility in water and ethanol) were determined. The properties of the liquid are depicted in Table 3, where the liquid was colorless with a nail polish-like smell. The liquid was highly soluble in ethanol and water; therefore, the unknown liquid is polar (Mohamed et al., 2021). The liquid boiled at 78.25 0C and had a calculated density of 0.7569 g/ml. The standard boiling point and density of ethanol are 78.29 0C and 0.7893 g/ml, respectively (Siddeeg et al., 2019). The values obtained in this lab were closely similar to the standard values. However, they deviated with 0.05 0C and 0.0334 g/ml errors. The errors are attributed to impurities and errors in the initial measurements of the masses of the unknown liquid. The boiling point and the solubility of the unknown liquid coincide highly standard values of ethanol. Therefore, the unknown liquid is ethanol (vinegar), but it is impure.
References
Mohamed, S. H., Salim, A. I., Issa, Y. M., & Ali, A. E. (2021). Detection and Identification of Adulteration in Vinegar Samples Based on Reversed-Phase High-Performance Liquid Chromatographic (RP-HPLC) Strategies. ACS Food Science & Technology, 2(1), 21-30. https://doi.org/10.1021/acsfoodscitech.1c00169
Siddeeg, A., Zeng, X. A., Rahaman, A., Manzoor, M. F., Ahmed, Z., & Ammar, A. F. (2019). Quality characteristics of the processed dates vinegar are influenced by ultrasound and pulsed electric field treatments. Journal of food science and technology, 56(9), 4380–4389. https://doi.org/10.1007/s13197-019-03906-3
Singh, A. K. (2020). Overview Of Vinegar Production. PalArch’s Journal of Archaeology of Egypt/Egyptology, 17(6), 4027–4037.
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