Chemistry: SI Units &amp; Conversions

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# Chemistry: SI Units & Conversions - PowerPoint PPT Presentation

Chemistry: SI Units &amp; 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

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

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