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PowerPoint Slides Shown Monday, Sept. 29 2008

PowerPoint Slides Shown Monday, Sept. 29 2008. CH142B. How to Solve Chemistry Problems. 1) Problem: States all of the information needed to solve the Problem. 2) Plan: Clarify the known and unknown .

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PowerPoint Slides Shown Monday, Sept. 29 2008

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  1. PowerPoint Slides Shown Monday, Sept. 29 2008 CH142B

  2. How to Solve Chemistry Problems 1) Problem: States all of the information needed to solve the Problem. 2) Plan: Clarify the known and unknown. Suggest the steps needed to find the solution. Develop a “roadmap”solution. 3)Solution: Calculations appear in the same order as outlined. 4) Check: Is the result what you expect or at least in the same order of magnitude! 5) Comment:Additional information as needed.

  3. A Sample Problem - I Length (km) of Fiber Length (m) of Fiber Mass (lb) of Fiber Mass (lb) of Cable International computer communications will soon be carried by optical fibers in cables laid along the ocean floor. If one strand of optical fiber weighs 1.19 x 10 -3 lbs/m, what is the total mass (in kg) of a cable made of six strands of optical fiber, each long enough to link New York and Paris? (8.85 x 103 km). Mass (kg) of Cable 1 km = 103 m 2.205 lb = 1 kg 1m = 1.19 x 10 -3 lb 6 fibers = 1 cable

  4. Sample Problem - II Length (m) of Fiber = 8.85 x 103 km x 103m / km = 8.85 x 106 m Mass (lb) of Fiber = 8.85 x 106 m x 1.19 x 10-3 lb / 1m = 1.05 x 104 lb Mass (lb) of cable = 1.05 x 104 lb / 1 fiber x 6 fibers / 1 cable = 6.30 x 104 lb / cable Mass (kg) of cable = 6.30 x 104 lb / 1 cable x 1kg / 2.205 lb = 2.86 x 104 kg / cable

  5. A Problem on Density - I Lengths (mm) of sides Mass (mg) of Li Lengths (cm) of sides Mass (g) of Li Volume (cm3) Density (g/cm3) of Li Lithium (Li) is a soft, gray solid that has the lowest density of any metal. If a slab of Li weighs 1.49 x 103mg and has sides that measure 20.9 mm by 11.1 mm by 12.0 mm, what is the density of Li in g/ cm3 ?

  6. Density Problem - II 1 g Mass (g) of Li = 1.49 x 103 mg x = 1.49 g Length (cm) of one side = 20.9 mm x 1cm / 10 mm = 2.09 cm Similarly, the other side lengths are 1.11 cm and 1.20 cm Volume (cm3) = 2.09 cm x 1.11 cm x 1.20 cm = 2.78 cm3 Density of Li = = 0.536 g/cm3 103 mg 1.49 g 2.78 cm3

  7. Like Problem on Density of a Metal Problem: Cesium is the most reactive metal in the periodic table, what is it’s density if a 3.4969 kg cube of Cs has sides of 125.00 mm each? Plan: Calculate the volume from the dimensions of the cube, and calculate the density from the mass and volume. Solution: length = 125.00 mm = 12.500 cm mass = 3.4969 kg x 1000g/kg = 3,496.9 g Volume = (length)3 = (12.500 cm)3 = 1,953.125 cm3 mass 3496.9 g density = = =1.7904 g/ml volume 1,953.125 cm3

  8. Temperature Scales and Interconversions Kelvin ( K ) - The “Absolute temperature scale” begins at absolute zero and only has positive values. Celsius ( oC ) - The temperature scale used by science, formally called centigrade and most commonly used scale around the world, water freezes at 0oC, and boils at 100oC. Fahrenheit ( oF ) - Commonly used scale in America for our weather reports, water freezes at 32oF, and boils at 212oF.

  9. Temperature Conversions T (in K) = T (in 0C) + 273.15 T (in 0C) = T (in K) - 273.15 T (in 0F) = 9/5 T (in 0C) + 32 T (in 0C) = [ T (in 0F) - 32] 5/9

  10. Definitions-I Matter- The “stuff” of the universe: books, planets, trees, professors - anything that has mass and volume. Composition - The types and amounts of simpler substances that make up a sample of matter. Properties - The characteristics that give each substance a unique identity. Physical Properties - are those the substance shows by itself, without interacting with another substance ( color, melting point, boiling point,density, etc.) Chemical Properties - are those that the substance shows as it interacts with, or transforms into, other substances (flammability, corrosiveness, etc.)

  11. Definitions - Mass & Weight Mass - The quantity of matter an object contains kilogram - ( kg ) - the SI base unit of mass, is a platinum - iridium cylinder kept in Paris as a standard! Weight - depends upon an object’s mass and the strength of the gravitational field pulling on it.

  12. Definitions - II Energy - The capacity to do work! Potential Energy - The energy due to the position of the object.Or Energy from a chemical reaction. Kinetic Energy - The energy due to the motion of the object.

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