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**lecturePLUS Timberlake**

An Introduction to Density by Helen Hanson & John Macaluso lecturePLUS Timberlake

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**lecturePLUS Timberlake**

Density Density is the ratio of the mass of an object to its volume D = mass = m volume V Units are g/cm3 Note: 1 mL = 1 cm3 lecturePLUS Timberlake

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**lecturePLUS Timberlake**

Learning Check 1 Osmium is a very dense metal. What is its density in g/cm3 if g of the metal occupies a volume of 2.22cm3? lecturePLUS Timberlake

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Solution Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass volume = g 2.22cm3 = g/cm3 = g/cm3 lecturePLUS Timberlake

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**lecturePLUS Timberlake**

Volume Displacement A solid displaces a matching volume of water when the solid is placed in water. 25 mL 33 mL 25 mL lecturePLUS Timberlake

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Learning Check 2 What is the density (g/cm3) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL? 1) 0.2 g/ cm3 2) 6 g/m3 3) g/cm3 33 mL 25 mL lecturePLUS Timberlake

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Solution 2) 6 g/cm3 Volume (mL) of water displaced = mL mL = mL Volume of metal (cm3) = 8 mL x 1 cm3 = cm3 1 mL Density of metal = mass = 48 g = 6 g/cm3 volume cm3 lecturePLUS Timberlake

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**Methods for Finding Volume**

The density can also be found by calculating the volume of an object and measuring its mass. height V=(length)(width)(height) width length lecturePLUS Timberlake

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Density of a Cylinder What is the density of a cylinder with a mass of 250.0g, a radius of 2.0 cm, and a height of 10.0 cm? r h lecturePLUS Timberlake

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Density of a Cylinder Vcylinder = лr2h = л x 5 x 5 x 10 (cm)(cm)(cm) = 250л cm3 r = radius h = height D = 250/(250л) g/cm3 D = m/V D =1/л g/cm3 m = g D = g/cm3 r h lecturePLUS Timberlake

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**lecturePLUS Timberlake**

Why Do Things Float? Things (whether solid, liquid or gas) with LESS density will float in a liquid with GREATER density. For example, this is why a stone (with HIGH density) will sink in water (LOW density), but a cork (LOW density) will float in water. lecturePLUS Timberlake

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Learning Check 3 Which diagram represents the liquid layers in the cylinder? (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL) 1) ) ) V W K W V K W K V lecturePLUS Timberlake

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Solution (K) Karo syrup (1.4 g/mL), (V) vegetable oil (0.91 g/mL,) (W) water (1.0 g/mL) 1) V W K lecturePLUS Timberlake

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**Density as Conversion Factors**

A substance has a density of 3.8 g/mL. Density = g/mL Equality g = 1 mL Conversion factors: 3.8 g and mL 1 mL g lecturePLUS Timberlake

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**lecturePLUS Timberlake**

Density Connections Mass Volume kg L g mL (cm3) mg lecturePLUS Timberlake

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**lecturePLUS Timberlake**

Learning Check The density of octane, a component of gasoline, is g/mL. What is the mass, in kg, of 875 mL of octane? 1) kg 2) 614 kg 3) 1.25 kg lecturePLUS Timberlake

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Solution 1) kg Unit plan: mL g kg Equalities: 1 mL = g and 1 kg = 1000 g Setup: 875 mL x g x kg = kg 1 mL g density metric factor factor lecturePLUS Timberlake

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Learning Check If blood has a density of 1.05 g/mL, how many liters of blood are donated if 575 g of blood are given? 1) L 2) L 3) L lecturePLUS Timberlake

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Solution 1) Unit Plan: g mL L 575 g x mL x 1 L = L 1.05 g mL lecturePLUS Timberlake

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**lecturePLUS Timberlake**

Learning Check A group of students collected 125 empty aluminum cans to take to the recycling center. If each can has a mass of 3g what volume of aluminum can be made if the cans were melted (Hint: d = 2.7 g/mL)? 1) L 2) 207 L 3) L lecturePLUS Timberlake

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Solution 1) 1.0 L 125 cans x 3g = 375g = mass 1 can So, V = mass = 375g = 139mL = 0.139L density g/mL lecturePLUS Timberlake

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Learning Check You have 3 metal samples. Which one will displace the greatest volume of water? 25 g Al 2.70 g/mL 45 g of gold 19.3 g/mL 75 g of Lead 11.3 g/mL lecturePLUS Timberlake

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Solution 1) 25 g Al x mL = 9.2 mL g 25 g Al 2.70 g/mL lecturePLUS Timberlake

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