Chem 1LD Practical Review Questions
With Complete Solutions
1. **Q: Before using the SpectroVis Plus, what must you do?**
- **A:** **Calibrate** the spectrometer .
2. **Q: What should you measure with a ruler before placing a cuvette in the spectrometer?**
- **A:** The **path length** (inner width) of the cuvette .
3. **Q: What is used as a "blank" to zero the instrument, and why?**
- **A:** **DI water** is used because it is the solvent for the dye .
4. **Q: Why must you wipe the outside of the cuvette and align it the same way each time?**
- **A:** Wiping removes smudges that scatter light. Aligning it the same way reduces systematic
errors (because cuvette walls vary in thickness) .
5. **Q: When performing a fluorescence experiment, how do you choose the correct excitation
wavelength (405 nm vs 500 nm)?**
- **A:** You choose the wavelength (e.g., 405 nm) that is closest to the **λmax** from the
absorption spectrum you previously took .
6. **Q: How do you determine the emission wavelength (λem) for fluorescence?**
, - **A:** You look for the wavelength where the sample gives off the **most light** (highest
intensity) on the fluorescence spectrum .
7. **Q: How do you create a calibration curve for the fluorometer?**
- **A:** Prepare a **serial dilution** of the stock solution (e.g., 100%, 50%, 25%, 12.5%) by mixing
the stock with pure solvent (heptane). Measure the fluorescence of each, then perform a **linear
regression** to get an equation .
8. **Q: What does the R² value on your calibration graph represent?**
- **A:** It represents how well the data fits the linear regression line (goodness of fit) .
### � Extraction & Separation Techniques
*Primarily from Experiment 8 (Chlorophyll) *
9. **Q: In a separatory funnel containing ethyl acetate and DI water, which layer is on top?**
- **A:** **Ethyl acetate** is the top layer because it is less dense than water .
10. **Q: Why do you need to remove the glass stopper before draining the separatory funnel?**
- **A:** If the stopper is not removed, a **vacuum** forms inside, preventing the liquid from
draining .
11. **Q: Why should you not shake the separatory funnel too vigorously?**
- **A:** Vigorous shaking can cause an **emulsion** (a mixture of the two layers that won't separate
easily) .
12. **Q: Why can we pour the aqueous layer (with food coloring) down the drain, but not the organic
layer?**
- **A:** The aqueous layer is water-miscible and non-hazardous (polar). The organic layer (e.g., ethyl
acetate/heptane) is **flammable** and non-miscible with water, requiring organic waste disposal .
13. **Q: What is the purpose of adding anhydrous MgSO₄ to the organic extract?**
- **A:** To **remove trace water** (dry the organic layer). The MgSO₄ absorbs the water and clumps
at the bottom .
### �🔬 Safety & Green Chemistry
With Complete Solutions
1. **Q: Before using the SpectroVis Plus, what must you do?**
- **A:** **Calibrate** the spectrometer .
2. **Q: What should you measure with a ruler before placing a cuvette in the spectrometer?**
- **A:** The **path length** (inner width) of the cuvette .
3. **Q: What is used as a "blank" to zero the instrument, and why?**
- **A:** **DI water** is used because it is the solvent for the dye .
4. **Q: Why must you wipe the outside of the cuvette and align it the same way each time?**
- **A:** Wiping removes smudges that scatter light. Aligning it the same way reduces systematic
errors (because cuvette walls vary in thickness) .
5. **Q: When performing a fluorescence experiment, how do you choose the correct excitation
wavelength (405 nm vs 500 nm)?**
- **A:** You choose the wavelength (e.g., 405 nm) that is closest to the **λmax** from the
absorption spectrum you previously took .
6. **Q: How do you determine the emission wavelength (λem) for fluorescence?**
, - **A:** You look for the wavelength where the sample gives off the **most light** (highest
intensity) on the fluorescence spectrum .
7. **Q: How do you create a calibration curve for the fluorometer?**
- **A:** Prepare a **serial dilution** of the stock solution (e.g., 100%, 50%, 25%, 12.5%) by mixing
the stock with pure solvent (heptane). Measure the fluorescence of each, then perform a **linear
regression** to get an equation .
8. **Q: What does the R² value on your calibration graph represent?**
- **A:** It represents how well the data fits the linear regression line (goodness of fit) .
### � Extraction & Separation Techniques
*Primarily from Experiment 8 (Chlorophyll) *
9. **Q: In a separatory funnel containing ethyl acetate and DI water, which layer is on top?**
- **A:** **Ethyl acetate** is the top layer because it is less dense than water .
10. **Q: Why do you need to remove the glass stopper before draining the separatory funnel?**
- **A:** If the stopper is not removed, a **vacuum** forms inside, preventing the liquid from
draining .
11. **Q: Why should you not shake the separatory funnel too vigorously?**
- **A:** Vigorous shaking can cause an **emulsion** (a mixture of the two layers that won't separate
easily) .
12. **Q: Why can we pour the aqueous layer (with food coloring) down the drain, but not the organic
layer?**
- **A:** The aqueous layer is water-miscible and non-hazardous (polar). The organic layer (e.g., ethyl
acetate/heptane) is **flammable** and non-miscible with water, requiring organic waste disposal .
13. **Q: What is the purpose of adding anhydrous MgSO₄ to the organic extract?**
- **A:** To **remove trace water** (dry the organic layer). The MgSO₄ absorbs the water and clumps
at the bottom .
### �🔬 Safety & Green Chemistry
