1. Chemistry: SI Units & Conversions

2. SI Base Units of Measure commonly used in chemistry
Time: second (s)
Length,distance: meter (m)
Mass: kilogram (kg)
In class, we consider the “base unit” to be grams.
Volume: liter (l)
Temperature: Kelvins (K) note: no degree symbol
In chemistry lab, we use the Celsius temperature scale. ( °C)

3. Derived Units
A derived unit is one in which the units are combined mathematically.
Volume: cubic centimeter (cm3)
(cm x cm x cm)
Area: square meter (m2)
( m x m)
Density: mass  volume

4. Converting Celsius to Kelvin
Kelvins = C + 273
°C = Kelvins - 273

5. Prefixes for SI Units Prefixes for units smaller than 1:
micro () 1 X 10-6 or
milli (m) 1 X or
centi (c) 1 X 10-2 or
deci (d) 1 X 10-1 or
Prefixes for units larger than 1:
kilo (k) 1 X 103 or 1,000

6. Conversion Using the Factor-Labeling Method : (Dimensional Analysis)
Starting unit
Target unit
Problem: Convert cm to m = X
Step 1: write down the starting measurement: number and unit!
Step 2: Convert from this prefix to the base unit. (This means meters, liters or grams.)
Step 5 If you have arrived at the target unit, you are done!
Be sure to include the unit and significant figures in your answer!
Step 3: Cancel the units that divide each other out.
Step 4: Perform the math… divide by the numbers on the bottom, multiply by the numbers on the top!

7. Practice! Convert 0.00450 km to cm ? X X =
The correct answer is 450 cm, but that’s only 2 sig figs…. ?????
Use scientific notation to correct the sig figs!
4.50 x 102 cm