Based on the description and the observed color changes in your experiment, let's analyze the results in a detailed, step-by-step manner.
### Step-by-Step Analysis:
1. Understanding the Controls:
- Positive Control (Gelatin): A positive control is a sample known to produce a positive (expected) result. Since gelatin contains protein, it should show a color change to pink/purple when Biuret solution is added, indicating the presence of protein.
- Negative Control (Water): A negative control is a sample known to produce a negative (expected) result. Pure water should not contain any protein and, when Biuret solution is added, it should not show any color change (should remain blue).
2. Analyzing the Mystery Food Sample:
- The mystery food sample should be tested in the same manner to determine if it contains protein, based on whether it shows a color change to pink/purple or remains blue.
### Observed Results in the Experiment:
- Gelatin (+ Control): Shows pink/purple (expected, indicating protein presence).
- Water (- Control): Shows pink/purple (unexpected, should remain blue, indicating no protein).
- Mystery Food Sample: Remains blue (indicating no protein).
### Identifying the Error:
- Discrepancy in the Negative Control:
- The negative control (Water) showing a pink/purple color is incorrect. The water should have remained blue, affirming it contains no protein. The observed pink/purple color suggests the presence of protein, which is not expected, hence there is an error.
### Possible Causes of the Error:
1. Contamination of the Biuret Solution:
- If the Biuret solution was contaminated with protein or another substance that could cause a color change, all samples tested would show a positive result, including the negative control.
2. Cross-Contamination of Samples:
- The water might have been contaminated with protein inadvertently during handling or labeling, leading to an incorrect positive result.
3. Incorrect Handling or Labeling of Samples:
- Errors in labeling or handling samples could lead to mixing up the controls, causing the negative control (water) to show unexpected results.
4. Faulty Reagent:
- There could be an issue with the Biuret reagent itself, giving false positive results.
### Conclusion:
The error in the experiment is evident from the fact that the negative control (water) showed an unexpected pink/purple color change, indicating a positive result where there should not be one. This result suggests an issue such as contamination, improper handling, or faulty reagents, leading to false positives. It is essential to address and correct these factors to ensure accurate and reliable results in future experiments.
