When placing a metal sample into a graduated cylinder to determine density by water displacement, the sample should be carefully and slowly slid down the side of the graduated cylinder into the water to avoid splashing or breaking the cylinder. The metal should be completely submerged without trapping air bubbles, as air bubbles can cause inaccurate volume measurements. The initial water volume should be recorded accurately, then the new water volume after adding the sample should be measured to determine the volume of water displaced by the sample, which equals the volume of the metal.
Two possible sources of error in this lab activity and how to minimize them are:
- Air Bubbles on the Metal Sample: Air bubbles can stick to the surface of the metal and increase the volume reading, leading to an overestimation of volume and thus density errors. To minimize this, ensure the metal sample is gently submerged and use a thin probe or gently tap the cylinder to dislodge any bubbles.
- Parallax Error Reading the Graduated Cylinder: Reading the volume measurement incorrectly by viewing the meniscus from an angle rather than eye level can cause error. To minimize this error, always read the graduated cylinder at eye level and use the bottom of the meniscus for the water volume reading.
Other general techniques to minimize error include ensuring the graduated cylinder is clean and dry before use and using consistent measurement techniques when handling equipment.
