1. PRE-AP CHEMISTRY PROBLEM SOLVING IN CHEMISTRY

2. Steps for solving word problems: 1. Find the unknown values. 2. Find the known values. 3. Plan a solution (let the units guide you). 4. Perform the calculations. 5. Check to see if it makes sense.

3. A conversion factor is a ratio with a value of one.  Ex. For example, one dollar is equal to 100 pennies.  1 dollar = 100 pennies or Dimensional Analysis is also called the “factor label method” of problem solving.  1 ft = 12 inches 1.00g water = 1 mL water 100 cm = 1m 1 dollar 100 pennies 1 dollar or

4. Ex. 52.5 m = ____ mm 52.5m 5.25 x 10 4 mm 1000 mm 1 m

5. Ex. 73.2 km = ____ cm 73.2 km = 7.32 x 10 6 cm 1m1km 100 cm 1000m

6. How many seconds are there in 2.5 years? 2.5 years = 78840000 or 7.9 x 10 7 s 1 year 365 days 1 hour 60 min 24 hours 1 day 60 sec 1 min

7. An average human heart beats 60. times per minute. If you live to be 82 years old, how many times will your heart beat? 82 years = 2,585,952,000 or 2.6 x 10 9 beats 1 year 365 days 1 hour 60 min 24 hours 1 day 60 beats 1 min

8. A clock gains 0.25 seconds per minute. How many seconds will it gain in exactly 180 days? 180 days 24 hr 60 min 0.25s gained 1 day 1 hr 1 min = 6.48 x 10 4 s gained or = 6.5 x 10 4 s gained

9. 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 1.00 zither 1 m 7.50 cm = 1330 zithers = 1333 zithers

10. 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

11. The density of dry air is measured at 25ºC is 1.19 x 10 -3 g/cm 3. What is the volume of 50.0 g of air? 50.0 g 1 cm 3 1.19 x 10 -3 g = 4.20 x 10 4 cm 3

12. Nolan Ryan threw a fastball 100.8 mi/h. Calculate this velocity in m/s. 1 mi = 1.6093 km. 45.06 m/s 1.6093 km 1 mi. 1000 m 1h 1 km 60 min 1 min 60 s 100.8 mi 1 h

13. The density of copper is 8.96g/cm 3 at 25 o C. Determine its density in kg/m 3. 8.96g 1 kg (100) 3 cm 3 1 cm 3 1000 g 1 m 3 =8960 kg/m 3 or 8.96 x 10 3 kg/m 3

14. 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 1000g man 1.1 x 10 -4 g Cu 2.2 lb man 1 kg man 100g man = 7.5 x 10 -2 g Cu or 0.075g Cu

15. In April 1996, the Department of the Interior released a “spike flood” from the Glen Canyon Dam on the Colorado River. Its purpose was to restore the river and the habitants along its bank. The release from the dam lasted exactly one week at a rate of 25,810 cubic feet of water per second. Assuming the density of the flood water was 1.000 g/mL, what was the total mass of the water released, in kg? 1 week = 4.42 x 10 11 kg 1 week 7 days 1 hour 3600 s 24 hours 1 day 25810 ft 3 water 1 s 1 3 ft 3 12 3 in 3 1 3 in 3 2.54 3 cm 3 1 cm 3 1 mL 1.000 g 1000 g 1 kg