Appendix A: The Tool Box 1 Cornerstone Chemistry Appendix A: The Tool Box Tool 1: The Laboratory NotebookThis is described in the opening pages of the manual. Tool 2: BalancesOne of the most important pieces of equipment a chemist uses is the balance. Balances come in different varieties serving different purposes. Two balances you will use is the triple beam balance for rough measurements and the electronic balance for more precise measurements. The triple beam works by counter balancing the weight of an object with a set of weights attached to the balance; its scale should be read to 0.1 grams since its uncertainty is of this order. The electronic balance does not employ any counter weights that must be moved; since it is a more sensitive instrument is can be read to 0.001 grams. These two balances, especially the electronic balance, are expensive and should be handled gently and left in good order (clean) after being used. Procedure for Weighing on a Triple Beam Balance 1. This balance has a plate on which the object to be weighed is placed, and three beams on which counter balancing weights are moved. First examine the balance especially the plate; see if it is free from any solids or liquids. 2. Move the weights on each of the three beams to the zero position. This will mean moving the 100 g weight, the 10 g weight, and the 1 gram weight to the leftmost notch. The pointer, located at the end of the balance opposite to the plate, should come to rest on the center line also known as the zero mark. When the pointer and the zero mark are aligned, the balance is zeroed. If you cannot zero your balance with the weights positioned in their leftmost notches, ask the instructor to adjust the balance before you proceed. 3. Once zeroed, the vessel or a piece of weighing paper that will hold your sample can be placed on the plate and its weight measured by moving the counter balancing weights until the pointer is aligned again with the zero mark. This is done by first moving the 100 g weight to the right, notch by notch, until the pointer goes below the zero mark. When the pointer goes below the zero balance mark, move the 100 g weight back to the left one notch. This procedure is repeated with the 10 g weight. The last weight, the 1 g weight, is moved until the pointer is aligned with the zero mark. At this point you take your measurement by summing together the individual weights which have been moved on the three beams. 4. The sample to be weighed is then added to the vessel and the previous procedure repeated. To find the mass of your sample, the difference between these weighings is calculated. This is called weighing by difference.
has intentionally blurred sections.
Sign up to view the full version.