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Dimensional Analysis or Unit Factor Method, or Unit Canceling are all names for the same concept. Simply put, the unit determine the math not the numbers. In other words,
UNITS, NOT THE NUMBERS ARE KING
Steps for Solving Mathematical Problems in Chemistry.
1. Write down unknown (units and in more complex problems what substance)
2. Write down all known units including conversion factors
A conversion factor is anything that allows you to go from one unit to another unit(s)For example, density it is a conversion factor between mass (g) and volume (cm3).
3. Setting up the answer. (Will not allow math equations)
- a. Write down known unit (only has one unit, multiple unit information are conversion factors)
- b. Write down conversion factor that will cancel known unit and get new unit (that is either desired unit or unit that will get you closer to desired unit). Keep on using more conversion factors until you get desired unit.YOU DO NO MATH IN THIS STEP
4. Do math (same math rules apply as in sig fig (SF) and scientific notation (SN) section).
- Remember:
- Number must be in scientific notation if greater than 1E3 or less than 1E-3
- One number before answer in N+1 (one more sig fig as in answer), correct SN and units
- Answer in correct SN, SF and units
5. Check answer to see if has correct units (answering question asked) and number makes physical sense!!!
Example: