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**Chemistry: SI Units & Conversions**

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**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)

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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

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**Converting Celsius to Kelvin**

Kelvins = C + 273 °C = Kelvins - 273

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**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

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**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!

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**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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Chapter 3. Measurement Measurement-A quantity that has both a number and a unit. EX: 12.0 feet In Chemistry the use of very large or very small numbers.

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