1 MEASUREMENT AND DENSITY ADDITIONAL READING The concepts in this experiment are also discussed in Sections 1.6 – 1.8 of Principles of Chemistry – A Molecular Approach , by Tro. ABSTRACT This experiment is divided into four parts. Each student is expected to perform the experiment individually. In part A you will determine the mass of a regular shaped object using two types of balances: a top loading balance and an analytical balance. You will familiarize yourself with the use and care of this equipment and compare under which conditions each type of balance should be used. Using a ruler provided by your instructor you will measure the height and diameter of a metallic cylinder and calculate its volume. From the mass of the cylinder and its volume you will determine its density. In parts B and C you will familiarize yourself with volume measurements using a graduated cylinder and a volumetric pipet to the proper number of significant figures. These techniques will be used countless times in this course, and it is important that you feel comfortable using, and correctly reading, the graduated cylinder and other equipment, such as pipets and burets. In addition, you will be introduced to the technique of “mass difference” which you will use frequently to help determine the mass of a component or object that cannot be weighed readily under normal conditions. You will use the volume and mass measurements to determine the density of two liquids: water and 95% ethanol, as well as examine the concepts of intensive and extensive properties. In part D you will further apply the techniques you have learned to determine the density of a regular shaped and irregular shaped metal sample applying Archimedes’ principle of water displacement. You will then use density to help you identify the sample. BACKGROUND M EASUREMENTS Chemistry involves a great deal of observation and measurement. It is important that when we are in the laboratory we clearly and carefully record our observations and measurements for future reference, since it is highly unlikely that we will be able to recall the exact values of measurements made. It is therefore imperative that you keep clear and detailed records so you can piece things together when you have left the lab. There are two general types of observations, qualitative and quantitative, that can be made. Qualitative observations are non-numerical observations: the color of copper chloride solution is blue, or, bubbles of gas are forming on the surface of zinc. Quantitative observations are numerical measurements, such as the mass of a particular beaker is 55.21 g, or the volume of water is 12.2 mL. It is important when making quantitative measurements not only to record the numerical value but also the units associated with the measurement.