What is Density? What is Density? • Biology – How many individuals per unit area? • Chemistry – How many particles per unit area? Units for Density • Density = mass/volume or D = m/v. • Density is the mass of an object divided by the volume • Units mass = gram (g) • Units volume = centimeters cubed cm3 or ml So, the overall units for density are g/cm3 or g/ml Density and Phases of Matter • Phases of matter are solids, liquids, gasses • Solids are the most dense objects because they have more particles close together and very little movement. • Liquids are next because the particles have more movement and are moving (flowing) around. The least dense liquid will collect on top of the most dense object. • Gasses are least dense because the particles are moving quickly past each other and are spaced far apart. Place the following substances in order from least dense to most dense. • • • • • Gases @ 293K or 20oC Unit is g/cm3 Hydrogen Helium Nitrogen Air Carbon Dioxide Place the following substances in order from least dense to most dense. Liquids Unit is g/ml • • • • • Methanol Water Formaline Carbon Tetrachloride Sulfuric acid Place the following substances in order from least dense to most dense. Solids Unit is g/cm3 • • • • • Aluminum Tin Iron Nickel Gold Regular Shaped Object • These are objects with fixed shapes, having defined edges like a rectangle or a square • To find the mass use a triple beam balance or an electronic balance using grams as the unit. • To find the volume you have to measure 3 sides of the object: length, width, height and multiply the numbers together. L x W x H = _____ cm3. Note that cm3 is the volume unit for a regular shaped object • Density unit for a RSO will be g/cm3 Practice A student in lab measured the mass of a rectangle to be 23.7 g. The length was 21.0 cm. The width was 7.0 cm. The height was 5.0 cm. What is the density of the object? Show all work and units!!! Answer V = L x W x H = 21.0cm x 7.0cm x 5.0cm = 735.0 cm3 or 7.4x102 cm3 D = Mass = 23.7 g = 0.032 g/cm3 Volume 7.4x102 cm3 2 Sig Figs Irregular Shaped Object • These are objects with no fixed shape and do not have defined edges like a rock or a cylinder. • To find the mass use a triple beam balance or an electronic balance using grams as the unit. • To find the volume you have to use the Water Displacement Method. Using a graduated cylinder place, enough water in the cylinder to cover the object. Place the ISO in the cylinder. The water level will rise. The difference between the starting volume and the ending volume will be the volume of the object. • So, use this equation: ending volume (EV) – starting volume (SV) = volume of object in ml. • Density unit for an ISO will be g/ml Practice Malia found a 10 g diamond in a mine in West Virginia. She wanted to know the volume of the diamond so she place 50 ml of water in a 100 ml graduated cylinder and after placing the diamond in the cylinder the water level rose to 75 ml. What is the density of the diamond? Show all work and units!!! Answer V = EV-SV = 75ml – 50ml = 25ml D = Mass = 10 g = 0.4 g/ml Volume 25 ml 1 Sig Fig Liquid • Liquids have no fixed shape because they take the shape of the container. • To measure the mass of a liquid, first mass an empty graduated cylinder in grams then pour some liquid into the cylinder and mass again. The difference between the ending mass and starting mass is the mass of the liquid. • So, use this equation: ending mass (EM) – starting mass (SM) = mass of object in g. • To get the volume just read the meniscus on the graduated cylinder. • Memorize: Water has a density of 1 g/ml no matter if the water is in China or the USA, pure water (H2O) has the same density everywhere. 1g = 1ml of H2O, 50g = 50ml H2O, 100g = _____ml H2O etc… Practice Jacob massed an empty graduated cylinder to be 58.0 g. He then put 28.0 ml of rubbing alcohol in a graduated cylinder. He then measured the object and the graduated cylinder to be 78.0 g. What is the density of the rubbing alcohol? Show all work and units!!! Answer M = EM-SM = M = 78.0g – 58.0g = 20.0g D = Mass = 20.0 g = 0.714 g/ml Volume 28.0 ml 3 Sig Figs Some questions ask you to find mass or volume, so you will need to rearrange the original equation D = Mass Volume M=VxD V = Mass Density