Chemistry
Chapter 2: Section 2 - Measurements and Calculations
Focus: Conversion Factors and Dimensional Analysis
Objectives:
1) Convert metric system units involving length, mass, volume, and time using dimensional
analysis (i.e. factor-label method).
How to do Dimensional Analysis:
*Conversion factor: by definition: fraction that always equals 1, which is used for dimensional
analysis.
EX: 1000 g = 1kg
EX2: 1 year = 365 days
EX3: 12 eggs = 1 dozen eggs
Steps:
1.
2.
3.
4.
5.
Take what you are given and put it over 1.
× _______
Bring down the unit ONLY!!!
Use a conversion factor. (Put the unit you are changing to on top).
If desired unit is on top, you are done. If NOT, repeat steps 2-4 until desired unit is on
top.
6. HOW TO GET THE ANSWER: input first number in your calculator; multiply by
numerators; divide by denominators (no need to multiply or divide by 1).
7. Cancel units to ensure proper set-up.
EX: Using dimensional analysis, find how many days are equal to 9,870,000 min?
1. Take what you are given and put it over 1:
9,870,000 min
1
2. × _______
9,870,000 min × _______
1
3. Bring down the unit ONLY!!!
9,870,000 min × _________
1
min
4. Use a conversion factor (must be an equivalent: 60 min = 1 hr)
9, 870,000 min ×
1
1 hr___
60 min
5. Desired unit is not on top (hours!!! We want days!!!) So repeat steps 2-4.
9, 870,000 min ×
1
1 hr___ ×
60 min
1 day__ =
24 hrs
6854.17 days
Here are some practice problems:
1. 3 hrs = ______ sec
2. 0.035 mg = ______ cg
3. 5.5 kg = _______ lbs
4. 2.5 yds = _______ in
5. 1.3 yrs = _______ hrs
Here are the answers to the practice problems:
1. 3 hrs = ______ sec
3 hr × 60 min
1
1 hr
× 60 sec
1 min
= 10800 sec
2. 0.035 mg = ______ cg
0.035 mg ×
1g
1
1000 mg
× 100 cg
1g
= 0.0035 mg
3. 5.5 kg = _______ lbs
5.5 kg × 1000 g
1
1 kg
×
1 oz
× 1 lb = 12.13 lbs
28.35 g
16 oz
4. 2.5 yds = _______ in
2.5 yd
1
× 3 ft × 12 in
1 yd
1 ft
= 90 in
5. 1.3 yrs = _______ hrs
1.3 yrs
1
× 365 days
1 yr
×
24 hrs
1 day
= 11388 hrs