# Chemistry: SI Units & Conversions - PowerPoint PPT Presentation

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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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## Chemistry: SI Units & Conversions

### 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)

### 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

### Converting Celsius to Kelvin

Kelvins = C + 273

°C = Kelvins - 273

### 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

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!

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