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Chemistry: SI Units & Conversions

Chemistry: SI Units & Conversions. 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

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Chemistry: SI Units & Conversions

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  1. Chemistry: SI Units & Conversions

  2. SI Base Units of Measurecommonly 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 10-3 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 32.05 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

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