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Chemistry 151 College of the Canyons Week 3 – Introduction to Volume, Mass, and Density Fall 2020 Name __________________________________ Date ____________________________ Section_________________________________ INTRODUCTION Volume is defined as the amount of space that is occupied by a solid object. Because liquids and gases also occupy space, they also have a volume. The metric unit for volume is the Liter (L). Volume can also be measured in cubic centimeters (cm3), or ‘cc’. One cubic centimeter is the volume of a cube that is 1 cm wide, 1 cm deep and 1 cm high. Because 1 mL is equal to 1 cm3, dimensional volumes can be easily converted to liters. The volume of a regularly-shaped solid is calculated depending on its shape and dimensions. (e.g. length, (l), height, (h), width, (w), and radius, (r)). The formulas for calculating the volume of a regularly-shaped solid are found in Table 1.1. Table 1.1 – Volume Formulas for Calculating Volumes of Regularly-Shaped Solids Volume of a Regularly-Shaped Solid Formula Cube lxwxh Sphere 4/3 πr3 radius = r = ½ the diameter Cylinder πr2h Many solids do not have a regular shape. The volume of these irregularly-shaped solids is determined by volume displacement, the volume of water that a solid displaces when it is immersed in water. An example of how to correctly calculate volume displacement is shown below. The density, d, of a substance is a physical property of matter that is defined as the mass per unit volume: 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 (𝑑𝑑) = 𝑚𝑚𝑚𝑚𝑑𝑑𝑑𝑑 (𝑚𝑚) 𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑚𝑚𝑑𝑑 (𝑣𝑣) Page 1 Chemistry 151 College of the Canyons Week 3 – Introduction to Volume, Mass, and Density Fall 2020 The density of a solid is generally measured in units of g/cm3, the density of a liquid in units of g/cm3 or g/mL, and the density of a gas in units of g/L. As density is a physical property, and the densities of most common substances are known, this property can also be used to identify a substance. Most liquids and solids have densities between 0.7 g/cm3 (gasoline) to 19.3 g/cm3 (gold). The densities of several common substances are found in Table 2.1 below. Unlike volume or mass, density is an intensive property, and is therefore independent of the amount of matter present. For example, the density of a platinum ring and a platinum vase will be the same regardless of their vast difference in size and mass. Chemistry by OpenStax is licensed under Creative Commons Attribution License v4.0 Table 2.1 – Densities of Common Substances The density of a liquid is determined by measuring the mass of the liquid “by difference” on a balance and measuring the volume of a liquid in a graduated cylinder or pipette by reading the bottom of the meniscus. The volume can also be determined using a more precise device for measurement, a buret. As discussed in Week 1, all measurements have some inherent error. Measurements can be characterized as both accurate, meaning the measured value is very near to the actual value, and precise, meaning that the measurement is reproducible. To communicate the precision of a measurement, scientists use significant figures. Various laboratory instruments have a different certainty of measurement. This uncertainty and subsequent number of decimal places needed for a measurement are specific to each instrument and can be found in the table below.