Question

The active ingredient of aspirin tablets is acetylsalicylic acid, which has a density of $1.4\mathrm{g}/{\mathrm{cm}}^3.$ In a lab class, a student used paper chromatography to isolate another common ingredient of headache remedies. The isolated sample had a mass of $0.384\mathrm{g}$ and a volume of $0.32{\mathrm{cm}}^3$. Given the data in the following table, what was the other ingredient in the headache remedy? $$\begin{array}{l}\text{ Density Values for Potential }\\ \text{ Headache Remedies }\\ \underline{\begin{array}{lc}\text{ Compound }& \text{ Density }\left(\mathrm{g}/{\mathrm{cm}}^3\right)\\ \text{ White table sugar }& 0.70\\ \text{ Caffeine }& 1.2\\ \text{ Acetylsalicylic acid }& 1.4\\ \text{ Sodium chloride }& 2.2\end{array}}\end{array}$$

Short answer

The other ingredient in the headache remedy is Caffeine, as its density (1.2 g/cm³) matches the calculated density of the isolated sample.

Step-by-step solution

Calculate the density of the isolated sample

To calculate the density of the isolated sample, we use the formula: $$Density=\frac{Mass}{Volume}$$ We are given the mass and volume of the isolated sample: Mass ($m$) = 0.384 g, Volume ($V$) = 0.32 cm³. Plug these values into the density formula: $$Density=\frac{0.384\text{g}}{0.32{\text{cm}}^3}$$

Compute the density value

Divide the mass by the volume to get the density of the isolated sample: $$Density=\frac{0.384\text{g}}{0.32{\text{cm}}^3}=1.2{\text{g/cm}}^3$$ The density of the isolated sample is 1.2 g/cm³.

Compare with given densities

Now we need to compare the density of the isolated sample (1.2 g/cm³) with the densities provided in the table. The table lists the following compounds and their respective densities: 1. White table sugar: 0.70 g/cm³ 2. Caffeine: 1.2 g/cm³ 3. Acetylsalicylic acid: 1.4 g/cm³ 4. Sodium chloride: 2.2 g/cm³ Comparing the calculated density of the isolated sample with the given densities, we find that it matches the density of Caffeine (1.2 g/cm³).

Conclusion

The other ingredient in the headache remedy is Caffeine, as its density matches the calculated density of the isolated sample.

Key concepts

Paper Chromatography

Paper chromatography is a simple and effective laboratory technique used for separating and identifying mixtures of substances. In educational settings, it's frequently introduced as a way to visually demonstrate the principles of mixture separation. The method involves applying a small sample of a mixture onto a piece of chromatography paper, and then placing one edge of the paper into a suitable solvent. As the solvent travels up the paper by capillary action, it carries along the substances in the mixture. These substances move at different rates due to differences in their affinities for the paper and the solvent, ultimately resulting in separation which can be visualized as different spots on the paper.

Once separated, each compound can be identified by comparing its position, known as the retention factor (Rf value), to those of known substances. In the context of the exercise, paper chromatography was used to isolate a common ingredient from a headache remedy, preparing it for further analysis such as density determination. By isolating the substance, it allows for a more accurate measurement of its physical properties.

Compound Identification

Compound identification is a fundamental process in chemistry that involves determining the components of a substance. Academically, it's a vital skill for students learning about the composition of various materials. Techniques like paper chromatography, spectral analysis, and mass spectrometry are commonly used for this purpose. In an educational lab scenario, identifying a compound generally involves comparing its characteristics against known standards. As demonstrated in the exercise, the identification was based on the density of an isolated sample, which was then matched to known density values of potential headache remedy ingredients. This method provided a clear and practical example of how physical properties can be used in the identification process. Understanding such methods prepares students for more complex analyses in professional scientific research.

Density Formula

The density formula is a fundamental concept in chemistry, defined as the mass of a substance per unit volume. It is mathematically expressed as $Density=\frac{Mass}{Volume}$. This formula is pivotal when students need to compute the density of various substances, like in this problem. To calculate the density of an object or substance, one must measure its mass (typically in grams) and its volume (often in cubic centimeters). The resulting density value has units of grams per cubic centimeter (g/cm³) and can serve as a distinctive property used to identify materials or to infer aspects of their composition and structure.

Density helps predict how substances will interact, such as whether an object will float in water or if one liquid will layer on top of another. The exercise provided a practical application by asking students to calculate the density of an isolated sample, reinforcing their understanding of both the concept and the calculation.

Mass-Volume Relationship

Understanding the mass-volume relationship is essential in the field of chemistry, particularly when dealing with concepts like density. This relationship is directly utilized when calculating the density of a substance, as seen in the exercise problem. Since density is mass divided by volume, knowing the relationship between these two properties allows students to understand how the amount of substance (mass) relates to the space it occupies (volume).

For instance, two samples of different substances may have the same volume but drastically different masses due to their specific densities. Learning about the mass-volume relationship through exercises such as density calculation equips students with the knowledge to predict the behavior of substances under various circumstances, like mixing, heating, or placing them in different environments. The relationship also underpins many real-world applications, such as designing objects with specific buoyancy characteristics or determining the dosage in medicinal compounding.