Question

During gravity filtration, a student forgets to heat the solution before running it through the filter. Aer capturing the filtrate, the student analyzes the sample via infrared (IR) spectroscopy and finds none of the desired product in the filtrate. What likely occurred to the student’s product? A. The product degraded because of a prolonged filtration time. B. The product evaporated with collection of the filtrate. C. The product precipitated and is present in the residue. D. The product was dissolved in the solvent.

Short answer

C. The product precipitated and is present in the residue.

Step-by-step solution

Understand the Scenario

Recognize the process described: during gravity filtration, a solution is filtered to separate solids from liquids. The instruction indicates that the solution was not heated before filtration.

Identify the Effect of Not Heating the Solution

Consider what happens to solubility when a solution is not heated. Usually, heating increases the solubility of solutes. Without heating, the product might not stay dissolved.

Analyze the IR Spectroscopy Results

The student found none of the desired product in the filtrate, meaning it wasn’t dissolved in the liquid that passed through the filter.

Consider the Scenario's Impact on the Product

If the product wasn't in the filtrate, it had to be somewhere else. Examine the potential locations: residue, evaporation, or degradation.

Evaluate Each Option

A. Degradation is unlikely without additional information or conditions causing it.B. Evaporation during common filtration is unlikely as the product would need very low boiling points.C. The product precipitating and ending up in the residue is likely since solubility decreases without heat.D. Dissolving in the solvent contradicts the observation of none in the filtrate.

Conclusion

With heating absent, solubility could have decreased, causing the product to precipitate and remain in the residue on the filter.

Key concepts

infrared spectroscopy

Infrared (IR) spectroscopy is a powerful tool used in organic chemistry to identify molecules based on their unique vibrational transitions. In this technique, molecules absorb infrared light at specific frequencies, causing their bonds to vibrate. These specific frequencies produce a spectrum that can be interpreted to identify functional groups within a molecule.
In the exercise scenario, the student utilized IR spectroscopy to analyze the filtrate. They found no presence of the desired product. This indicates the product was not present in the form that IR spectroscopy can detect, usually meaning it was neither in solution nor in a detectable form within the solvent. This absence helps pinpoint where the product likely ended up, guiding us to explore other possibilities, like precipitation.

solubility and temperature

Solubility is a critical concept in chemistry, describing how well a substance (solute) dissolves in a solvent. The solubility of many compounds is temperature-dependent: higher temperatures typically increase solubility.
In the given problem, the student forgot to heat the solution before filtration. This oversight is significant because without heating, the solubility of their product may have drastically reduced. An unheated solution often leads to the solute coming out of the solution, especially if the solute's solubility is significantly higher at elevated temperatures.
This change in solubility explains why the desired product was not found in the filtrate—it precipitated out of the solution instead of remaining dissolved.

precipitation during filtration

Precipitation occurs when a solute becomes insoluble in the solvent, forming solid particles that separate from the solution. This process is strongly influenced by temperature and the solubility properties of the materials involved.
When the solution wasn't heated in the described experiment, the solubility of the product likely decreased, causing it to precipitate. During gravity filtration, these precipitates cannot pass through the filter and instead, remain in the residue.
Given that IR spectroscopy revealed no product in the filtrate, it supports the conclusion that the product indeed precipitated and localized within the solid residue on the filter. Therefore, this residue should be analyzed to recover the desired product.