Advanced Chemistry Notes 3.4 Density, Percent Error and Temperature 3.4a Density Calculations Density = 𝒎𝒂𝒔𝒔 𝒗𝒐𝒍𝒖𝒎𝒆 or D = 𝒎 𝒗 Density - is an important intensive property, which can be used to help determine the identity of an unknown substance. 2 Ways to Measure the Volume of a Solid 1. 2. Solid object regular sides (L x W x H) using a ruler Water displacement. Place irregularly shaped solid into a volumetric cylinder half filled with water and place solid into the cylinder and subtract both volumes Exercise 1 Density 1. A student determines that a piece of an unknown material has a mass of 5.854 g and a volume of 7.57 cm 3. What is the density of the material, to the correct number of significant digits? 2. Iron has a known density of 7.87 g/cm3. What would be the mass of a 2.4 cm3 piece of iron? 3. Mercury has a density of 13.5 g/cm3. How much space would 50.0 g of mercury occupy? Exercise 2 Determining Density A chemist, trying to identify the main component of a compact disc cleaning fluid, finds that 25.00 cm3 of the substance has a mass of 19.625 g at 20C. The following are the names and densities of the compounds that might be the main component. Compound Chloroform Diethyl ether Ethanol Isopropyl alcohol Toluene Density in g / cm3 at 20 C 1.492 0.7140 0.7890 0.7850 0.8670 Which of these compounds is the most likely to be the main component of the compact disc cleaner? 3.4b Percent Error or Experimental Error Expresses as a percentage the difference between an approximate or measured value and an exact or known value. Advanced Chemistry Notes 3.4 𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝐸𝑟𝑟𝑜𝑟 = | 𝑉𝑎𝑙𝑢𝑒𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 − 𝑉𝑎𝑙𝑢𝑒 𝐴𝑐𝑐𝑒𝑝𝑡𝑒𝑑 𝑉𝑎𝑙𝑢𝑒 𝐴𝑐𝑐𝑒𝑝𝑡𝑒𝑑 | x 100% Exercise 3 Determining percent Error 1. Working in the laboratory, a student find the density of a piece of pure aluminum to be 2.85 g/cm3. The accepted value for the density of aluminum is 2.699 g/cm3. What is the student's percent error? 2. A student experimentally determines the specific heat of water to be 4.29 J/g x Co. He then looks up the specific heat of water on a reference table and finds that is 4.18 J/g x Co. What is his percent error? 3.4c Temperature Temperature – is the average kinetic energy of a substance. Some important temperatures: o 0 C = Water Freezes o 100 C = Water Boils o 37 C = Normal Body Temperature o 20 C = Ambient Room Temperature Convert from degree Celsius to Fahrenheit Fo = 9/5 Co +32 32 is an exact number Convert from Fahrenheit to degree Celsius Co = 5/9 (Fo-32) o Kelvin: - temperature scale where 0 K (absolute zero) = -273.15 C (particles stop moving) Tk = Tc + 273 Exercise 4 Convert the following to Fahrenheit 1) 10o C ________ Exercise 5 Convert the following to Celsius 1) 32o F ________ Exercise 6 Convert the following to Kelvin 1) 0o C ________ Temperature C o to F o 2) 33.3o C ________ 3) 46.9o C ________ Temperature F o to C o 2) 45o F ________ 3) 70.1o F ________ Temperature C o to K 2) -50o C ________ 3) 90o C ________ 35 mi / gal Advanced Chemistry Exercise 7 Convert the following to Celsius 1) 134 K ________ Notes 3.4 Temperature K to C o 2) 265 K ________ 3) 273 K ________ Practice Problems 1. A loaf of bread has a mass of 500 g and volume of 2500 cm 3. What is the density of the bread? 2. A block of wood has a mass of 6.0 g and a volume of 12.0 cm3. What is the density of the block of wood? 3. The density of a substance is 4.0 g/cm3. If a sample of the substance has a volume of 25 cm3, then what is its mass? (Hint: Use the equation: mass = density × volume.) 4. You have a lead ball with a mass of 420 g. The density of lead is 10.5 g/cm3. What is the volume of the ball? (Hint: Use the equation: volume = mass/density.) 35 mi / gal 5. A student has a rectangular block. It is 2 cm wide, 3 cm tall, and 25 cm long. It has a mass of 600 g. First, calculate the volume of the block: Then, use that answer to determine the density of the block: 6. Joshua uses his thermometer and finds the boiling point of ethyl alcohol to be 75 o C. He looks in a reference book and finds that the actual boiling point of ethyl alcohol is 80 oC. What is his percent error? 7. The density of water at 4oC is known to be 1.00 g/mL. Kayla experimentally found the density of water to be 1.075 g/mL. What is her percent error? 8. The Handbook of Chemistry and Physics lists the density of a certain liquid to be 0.7988 g/mL. Taylor experimentally finds this liquid to have a density of 0.7925 g/mL. What is his percent error? 9. An object has a mass of 35.0 grams. On Anthony’s balance, it weighs 34.85 grams. What is the percent error of his balance?