1. Measurement in Chemistry Factor-Label Method

2. The Factor-Label Method At the conclusion of our time together, you should be able to:
Recognize a problem that can be solved with the factor label method
Transform a statement of equality into a conversion factor
Use the appropriate conversion factor in the correct way so that the labels cancel and the correct conversion is found

3. The Factor label Method
A way to solve math problems in chemistry
Used to convert
km to miles, m to km, mol to g, g to mol, etc.
To use this we need:
1) given quantity
2) desired quantity
3) conversion factors
Conversion factors are valid relationships or equalities expressed as a fraction and equal to one!

4. Conversion Factors Example: 1 in. = 2.54 cm
Fractions in which the numerator and denominator are EQUAL quantities expressed in different units but always equal to one. You can always multiply any equation by this equality and not change the quantity, just the units.
Example: in. = 2.54 cm
Factors: in and cm
2.54 cm in.

5. The Steps to Follow
Now we are ready to solve problems using the factor label method. The steps involved are:
Write down the given quantity
Determine what conversion factors you will use to turn the given label into the needed label.
Set up the conversion factors
Given unit in the denominator
Desired unit in the numerator
Complete the math

6. Factor label Example
How many kilometers are in 47.0 miles? (note: 1 km = miles)
How many miles are in 23.4 kilometers?

7. Summary The previous problem was not that hard
In other words, you probably could have done it faster using a different method
However, for harder problems the factor label method is easiest

8. Measurement in Chemistry Factor-Label Method Part 2

9. Converting Metric to Metric
Steps
Write the given quantity
Set up units in the conversion factor
Larger prefix gets a 1
Determine what goes in front of smaller prefix
Cancel units
Complete the math

10. Converting Metric to Metric
A rattlesnake is 2.44 cm long. How long is the snake in mm?

11. Converting Metric to Metric 2
An atom has a volume of 35.67nL. What is its volume in cL?

12. Converting Metric to Metric 3
Max has a mass of 125kg. What is this in micrograms?

13. Measurement in Chemistry Factor-Label Method Part 3

14. Dealing with Two Units Convert 55.00 km/h to m/s
km x m x 1 h___ =
h km s
15.28 m/s

15. Dealing with Two Units, Your Turn
If your pace on a treadmill is 65 meters per minute, what is your rate in km per hour

16. What about Square and Cubic units?
Use the conversion factors you already know, but when you square or cube the unit, don’t forget to cube the number also!
Best way: Square or cube the Entire conversion factor
Example: Convert 4.3 cm3 to mm3
( )
4.3 cm mm 3
1 cm
4.3 cm mm3
13 cm3 =
= 4300 mm3

17. Learning Check
A Nalgene water bottle holds 1000 cm3 of dihydrogen monoxide (DHMO). How many cubic decimeters is that?

18. Solution
( )
1000 cm dm 3
10 cm
= 1 dm3
So, a dm3 is the same as a Liter!
A cm3 is the same as a milliliter.

19. Learning Check
A person’s blood contains 185 mg of cholesterol per deciliter of blood. How many grams of cholesterol are there in 1 liter of this blood? g
0.185 g
1.85 g
18.5 g
1850 g