Density Volume University of North Carolina （北卡罗莱纳大学密度卷）.pdfVIP

2s Density Volume OBJECTIVES • To extend the concepts of proportional relationships to intensive properties of substances. • To accurately measure the densities of common household substances • To apply density relationships in problem solving. INTRODUCTION Remember the old joke, Which is heavier a pound of lead or a pound of feathers? Even though a pound is always a pound, we think of lead as being heavier than feathers because lead has such a large density. Density is defined as mass per unit volume; mathematically, we would write: mass m density or d Volume V For any pure substance or homogenous mixture, density is an intensive quantity, which means that its value is the same no matter how much of the substance is present. Density expresses the proportional relationship between mass and volume of the substance. If the density of a particular substance is given in grams per milliliter, it indicates the number of grams present in 1 milliliter of that substance. Conversely, the reciprocal of density tells the number of milliliters present in one gram of the substance. For example, the density of copper is 8.94 g/cm3. This tells us that: 1 cm3 of copper 1 gram of copper Figure 2.1 1. A sample of copper with a one cubic centimeter volume weighs _______ grams. 3 2. A one gram sample of copper occupies a volume of ______ cm . To determine density, the mass and volume of a sample of material must be measured. Figure