Make a second dilution by adding \(1.0 \mathrm{~mL}\) of the \(10^{-1}\) dilution to one of the \(9.0 \mathrm{~mL}\) dilution tubes. Mix well. This dilution contains \(1 / 100\) original sample and is \(10^{-2}\).

The dilution factor is a key concept when working with serial dilutions. It tells us how much a sample's concentration has been reduced. In each step of dilution, we divide the original concentration by a certain number.

For example, in this exercise, starting with a dilution factor of \(10^{-1}\) means the original concentration is reduced to one-tenth. When we take \(1.0 \, \text{mL}\) from this \(10^{-1}\) sample and add it to \(9.0 \, \text{mL}\), the concentration of the sample becomes \(10^{-2}\), or one-hundredth of the original. This is because \(10^{-1} \times 10^{-1} = 10^{-2}\).

Understanding dilution factors helps ensure accurate results in experiments. They allow for precise control over the concentration of a substance. Essentially, you can systematically decrease the concentration across a series of steps.

Good laboratory techniques are crucial in achieving reliable results. In this exercise, there are several key techniques to consider:

• Accurate Measurement: Using pipettes or syringes precisely measure \(1.0 \, \text{mL}\). This accuracy is critical for consistency.
• Proper Mixing: After combining the samples, mixing thoroughly is essential. This ensures even distribution of the diluted substance.
• Maintaining Cleanliness: Proper sterilization and cleanliness of equipment prevent contamination. Using sterilized tubes for diluents helps keep samples pure.
• Following Protocols: Adhering to specific mixing and handling protocols ensures replicable and valid results.

Mastering these techniques ensures that each dilution is accurate, and the results are reliable and reproducible. Lab techniques form the foundation for various scientific experiments.

Sample preparation is the initial, yet crucial step in any laboratory experiment. It involves readying the sample for dilution or analysis. Here’s what you need to keep in mind:

• Starting With a Clean Sample: Ensure the sample is pure and clean to avoid contamination.
• Labeling: Clearly label all tubes and containers to avoid mix-ups. This helps track samples through multiple dilutions.
• Accurate Measurements: Start with precise measurements. Using calibrated equipment to measure \(1.0 \, \text{mL}\) and \(9.0 \, \text{mL}\) is key.
• Gentle Handling: Handle all equipment and samples gently to maintain integrity.
• Initial Dilution: Prepare the initial sample by diluting it correctly before beginning serial dilutions.
  
  These steps in sample preparation ensure the experiment starts on a solid foundation. Accurately prepared samples lead to more reliable and credible results in the dilution process.