• In this process, numbers and units are equally important.
• Conversion factors are:
  • Relationships that convert one quantity to another.
  • A fraction (ratio) equivalent to one.
  • Here is a page of useful conversion factors.
• Multiply what is given by fractions equal to one to convert units. Always be sure the unit to be eliminated is correctly placed in the conversion factor. If the unit to be eliminated is in the numerator of the given information, then the unit must be placed in the denominator of the conversion factor. Since the numerator and denominator of any conversion factor are equivalent, they may be flipped as needed.
• The diagram below shows how all factor-label problems will be "set up" in this class. The horizontal line represents "divide by", vertical lines represent "multiply by".
  

• Always begin your problem by writting down what is given in the problem, then drawing the horizontal and vertical lines. Another vertical line is drawn each time a different conversion factor is used.
• As you begin using the factor-label method, get into the habit of putting a line through the units as they "divide out". The only units that are not "canceled" should be the correct units of the final answer. When all units have been canceled except those needed for the final answer, you are ready to pick up your calculator and find the number.

• Convert 1000 grams to pounds. It is known that one pound is equal to 454 grams. This becomes the conversion factor needed to work the problem.

  

• Convert 65 miles/hour to meters/second. There are two different units in this problem. Treat them seperately. It does not matter which unit you solve first, as long as you complete its conversion before going to the other. In the diagram below, the problem is solved with two conversion factors. However, if you don't know how many seconds are in an hour or how many meters are in a mile, you can break them into relationships you do know:
  • 1 hour/60 minutes . . . 1 minute/60 seconds
  • 5280 feet/1 mile . . . 12 inches/1 foot . . . 1 inch/2.54 centimeters . . . 100 centimeters/1 meter

  

1. Use conversion factors from the SI system to do the following conversions:
   1. 2.4 meters to centimeters
   2. 65.5 centigrams to milligrams
   3. 5 liters to cubic decimeters
   4. The density of a substance is 2.7 g/cm³. What is the density of the substance in kilograms per liter?
2. A car is traveling 65 miles per hour. How many feet does the car travel in one second?
3. The density of water is one gram per cubic centimeter. What is the density of water in pounds per liter?
4. How many basketballs can be carried by 8 buses?
   • 1 bus = 12 cars
   • 3 cars = 1 truck
   • 1000 basketballs = 1 truck

     

Chemistry Class

  Practice Problem Answers:

1. 1. 240 cm
   2. 655 mg
   3. 5 dm³
   4. 2.7 kg/L
2. 95 ft/sec
3. 0.45 lb/L
4. 32 000 basketballs