WS1_key - Chem 142 Name...

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Unformatted text preview: Chem 142 Name ________________________________________ Worksheet 1: Unit Conversion Summer 2011 Section ________________ 1. The volume of an irregularly shaped solid can be determined from the volume of water it displaces. A graduated cylinder contains 245.0 mL water. When a small piece of Pyrite, an ore of iron, is submerged in the water, the volume increases to 315.8 mL. What is the volume of the piece of Pyrite in cm3 and in liters? 1 mL = 1 cm3 = 0.001 L V ( mL ) = 315.8mL ! 245.0mL = 70.8mL V cm 3 = 70.8mL ! V ( L ) = 70.8mL ! ( ) 1cm 3 = 70.8cm 3 1mL 1L = 7.08 ! 10 "2 L 1000mL 2. Dry ice (solid carbon dioxide (CO2)) undergoes sublimation, the process by which a solid converts to a gas, under standard conditions. A sample of dry ice weighs 6.54 lbs. After 0.5 hrs, 3.76 lbs of dry ice remains. At what rate is the dry ice sublimating in kg/min and g/s? 1 kg = 2.21 lbs = 1000 g rate ( lbs hr ) = 6.54lbs ! 3.76lbs = 5.56 lbs hr 0.5hr ! 0hr 5.56lbs 1kg 1hr ! ! = 4.2 ! 10 "2 kg min hr 2.21lbs 60min rate ( kg min ) = 4.2 ! 10 "2 kg 1000g 1min rate ( g s ) = ! ! = 7.0 ! 10 "1 g s min 1kg 60s Page 1 of 2 Chem 142 Summer 2011 3. A 1.5 mL DNA sample dissolved in water must be frozen before it can be lyophilized (freeze-dried). The freezer will freeze the sample at a rate of 0.5 cm3/hr. A bucket of dry ice will freeze the sample as a rate of 0.1 cm3/min. How much time will be saved by freezing the sample in dry ice vs. the freezer in hours? t freezer 1hr 1cm 3 = ! ! 1.5mL = 3hrs 0.5cm 3 1mL 1min 1hr 1cm 3 ! ! ! 1.5mL = 0.25hr 0.1cm 3 60 min 1mL t dry ice = t saved = t freezer ! t dry ice = 3hr ! 0.25hr = 2.75hr 4. A stainless steel ball bearing has a radius of 6.35 mm and a density of 7.75 g/cm3. Iron is the principle element in steel. Carbon is a key minor element. The ball bearing consists of 0.25% carbon (C), by mass. What mass of the ball bearing is due to C in g and mg? 1 cm = 10 mm Vsphere = 4 3 !r 3 3 Vball bearing 4 # 1cm & 3 = ! % 6.35mm " ( = 1.07cm 3 $ 10mm ' 7.75g = 8.31g 1cm 3 massball bearing = 1.07cm 3 ! masscarbon ( g ) = 8.31g ! 0.25% = 2.08 ! 10 "2 g 100% masscarbon ( mg ) = 2.08 ! 10 "2 g ! 1000mg = 20.8mg 1g Page 2 of 2 ...
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