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 symbolIn chemistry lab, we use the Celsius temperature scale. ( °C)
3 Derived UnitsA 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
5 Prefixes for SI Units Prefixes for units smaller than 1: micro () 1 X 10-6 ormilli (m) 1 X orcenti (c) 1 X 10-2 ordeci (d) 1 X 10-1 orPrefixes for units larger than 1:kilo (k) 1 X 103 or 1,000
6 Conversion Using the Factor-Labeling Method : (Dimensional Analysis) Starting unitTarget unitProblem: Convert cm to m=XStep 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