why must a clean rod be used each time?

Are you eating with it? building a fire with it? scratching your back with it? what?

no like when you use it in an experiment of a precipitate

You don't want to take the chance of contaminating the ppt. Frankly, I think it's ok to stir with a glass rod, rinse it thoroughly with water from a wash bottle, and reuse the same glass rod as long as it hasn't been in contact with any other surface (meaning that you hold the glass rod in your hand until ready to use it again AND you don't let the part of the glass rod that will be dipped into the solution or ppt touch anything.).

thanks alot!!

oh another question pliz... why different masses of ppt were obtained for test tube IV and V??... LAB QUESITONS

Aw C'mon. I'm not a mind reader. What ppt? What masses? What chemicals? What experiment? What's in test tube IV and V initially and what was added to each?

A clean rod must be used each time for several reasons. First, it helps maintain the accuracy and precision of measurements. When a rod comes into contact with different substances or contaminants, such as dust, oil, or residue from previous experiments, it can affect the readings and introduce errors. Using a clean rod ensures that the measurement is not influenced by these external factors.

Second, using a clean rod reduces the risk of cross-contamination. If a rod is used for multiple samples without being cleaned in between, it can lead to contamination of one sample with residues from another. This can compromise the integrity of the experiments and result in inaccurate or unreliable data.

To ensure a clean rod each time, you can follow these steps:

1. Start with a clean and dry rod: Before starting any measurements, make sure the rod is clean and dry. If necessary, wipe it with a lint-free cloth or tissue to remove any visible contaminants.

2. Avoid touching the rod with bare hands: When handling the rod, avoid direct contact with your hands, as they may contain oils, dirt, or other substances. Use gloves or hold the rod with a clean cloth or tissue.

3. Clean the rod between measurements: After each measurement or sampling, clean the rod to remove any residue. You can use a suitable cleaning agent, such as ethanol or distilled water, along with a clean cloth or tissue. Gently wipe the entire surface of the rod to ensure thorough cleaning.

4. Store the rod properly: Once cleaned, store the rod in a clean and dry place, away from potential contaminants. This will help maintain its cleanliness for future use.

By following these steps and using a clean rod each time, you can ensure accurate and reliable measurements while minimizing the risk of cross-contamination.