Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Chapter 1 Chemistry and Measurements Density Objects that sink in water are more dense than water; objects that float in water are less dense.

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Density 2 compares the mass of an object to its volume is the mass of a substance divided by its volume Density Expression Density = mass = g or g or g/cm 3 volume mL cm 3 Note: 1 mL = 1 cm 3

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 3 Densities of Common Substances

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Calculating Density 4

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check 5 Osmium is a very dense metal. What is its density in g/cm 3 if 50.0 g of osmium has a volume of 2.22 cm 3 ? 1) 2.25 g/cm 3 2) 22.5 g/cm 3 3) 111 g/cm 3

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. 6 Step 1 State the given and needed quantities. Given: 50.0 g; 22.2 cm 3 Need: density, g/cm 3 Step 2 Write the density expression. D = mass volume Step 3 Express mass in grams and volume in mL or cm 3. Mass = 50.0 g Volume = 22.2 cm 3 Step 4 Substitute mass and volume into the density expression and calculate. D = 50.0 g = g/cm cm 3 = 22.5 g/cm 3 (rounded to 3 SFs) Solution

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Volume by Displacement A solid completely submerged in water displaces its own volume of water has a volume calculated from the volume difference 45.0 mL − 35.5 mL = 9.5 mL = 9.5 cm 3 7

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Density Using Volume Displacement The density of the zinc object is calculated from its mass and volume. Density = mass = g = 7.2 g/cm 3 volume 9.5 cm 3 8

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check 9 What is the density (g/cm 3 ) of a 48.0-g sample of a metal if the level of water in a graduated cylinder rises from 25.0 mL to 33.0 mL after the metal is added? 1) 0.17 g/cm 3 2) 6.0 g/cm 3 3) 380 g/cm 3 object 33.0 mL 25.0 mL

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution 10 Step 1 State the given and needed quantities. Given: 48.0 g Volume of water = 25.0 mL Volume of water + metal = 33.0 mL Need: Density Step 2 Write the density expression. Density = mass of metal volume of metal

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution 11 Step 3 Express mass in grams and volume in mL or cm 3. Mass = 48.0 g Volume of the metal is equal to the volume of water displaced. Volume of water + metal = 33.0 mL − Volume of water = 25.0 mL Volume of metal= 8.0 mL

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution 12 Step 4 Substitute mass and volume into the density expression and calculate the density. Density = 48.0 g = 6.0 g = 6.0 g/mL 8.0 mL 1 mL

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Sink or Float Ice floats in water because the density of ice is less than the density of water. Aluminum sinks because its density is greater than the density of water. 13

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check 14 Which diagram correctly represents the liquid layers in the cylinder? Karo syrup (K) (1.4 g/mL); vegetable oil (V) (0.91 g/mL); water (W) (1.0 g/mL) K K W W W V V V K

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution 15 1) vegetable oil 0.91 g/mL water 1.0 g/mL Karo syrup 1.4 g/mL K W V

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Problem Solving Using Density 16 Density can be written as an equality. For a substance with a density of 3.8 g/mL, the equality is 3.8 g = 1 mL From this equality, two conversion factors can be written for density. Conversion 3.8 g and 1 mL factors1 mL 3.8 g

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Problem Solving Using Density 17

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check 18 The density of octane, a component of gasoline, is g/mL. What is the mass, in kg, of 875 mL of octane? A kg B. 614 kg C kg

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution 19 The density of octane, a component of gasoline, is g/mL. What is the mass, in kg, of 875 mL of octane? Step 1State the given and needed quantities. Given: Density of octane = g/mL Volume = 875 mL Needed: Mass of octane Step 2 Write a plan to calculate the needed quantity. Density Conversion factor Plan: milliliters grams kilograms

Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution 20 The density of octane, a component of gasoline, is g/mL. What is the mass, in kg, of 875 mL of octane? Step 3 Write equalities and their conversion factors including density. density g = 1 mL and 1 kg = 1000 g Step 4 Set up problem to calculate the needed quantity. 875 mL x g x 1 kg = kg 1 mL 1000 g Answer is A, kg.