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CHEMISTRY CHAPTER 4 PROBLEM SOLVING IN CHEMISTRY Steps for solving word problems: 1. 2. 3. 4. 5. Find unknown Find knowns Plan solution Calculate Check A conversion factor is a ratio with a value of one. Ex. 1 ft = 12 inches 1.00g water = 1 mL water 100 cm = 1m Dimensional Analysis is also called the “factor label method” of problem solving. Ex. 52.5 m = ____ mm 52.5 m x 1000 mm 1m or = 5.25 x 104 mm 52.5m 1000mm = 5.25 x 104 mm 1m Ex. 73.2 km = ____ cm 73.2 km 1000m 1 km 73.2 km 1000m 100 cm 1 km 1m = 7.32 x 106 cm How many seconds are there in 2.5 years? 2.5 years 365 days 1 year 2.5 years 365 days 1 year 2.5 years 365 days 1 year 2.5 years 365 days 1 year = 7.9 x 107 s 24 hours 1 day 24 hours 1 day 24 hours 1 day 60 min 1 hour 60 min 60 s 1 hour 1 min A clock gains 0.25 seconds per minute. How many seconds will it gain in exactly 180 days? 180 days 24 hr 1 day 180 days 24 hr 1 day 180 days 24 hr 1 day 60 min 1 hr 60 min 0.25s gained 1 hr 1 min =6.48 x 104 s gained = 6.5 x 104 s gained A fictitious unit of length called the “zither” is defined by the relationship 7.50 cm = 1.00 zither. How many zithers are in a 100.0 meter distance? 100.0m 100cm 1m 100.0m 100cm 1.00 zither 1m 7.50 cm = 1333 zithers = 1330 zithers What is the mass of a 35.0 mL sample of concentrated sulfuric acid (density 1.84g/mL)? 35.0 mL 1.84g 1 mL = 64.4 g Nolan Ryan threw a fastball 100.8 mi/h. Calculate this velocity in m/s. 1 mi = 1.6093 km. 100.8 mi 1h 100.8 mi 1.6093 km 1h 1 mi. 100.8 mi 1.6093 km 1000 m 1h 1 mi. 1 km 100.8 mi 1.6093 km 1000 m 1hr 1h 1 mi. 1 km 60 min 100.8 mi 1.6093 km 1000 m 1hr 1 min 1h 1 mi. 1 km 60 min 60 s 45.06 m/s The density of copper is 8.96g/cm3 at 25oC. Determine its density in kg/m3. 8.96g 1 cm3 8.96g 1kg 1 cm3 1000g 8.96g 1kg (100)3cm3 1 cm3 1000g 1m3 =8960 kg/m3 or 8.96 x 103 kg/m3 Copper makes up 1.1 x 10-4 percent by mass of a normal healthy human. How many grams of copper would be found in the body of a person weighing 150 lb? (1.0 kg = 2.2 lb) 150 lb man 1.0kg man 2.2 lb man 150 lb man 1.0kg man 1000g man 2.2 lb man 1 kg man 150 lb man 1.0kg man 1000g man 1.1 x 10-4g Cu 2.2 lb man 1 kg man 100g man = 7.5 x 10-2 g Cu or 0.075g Cu