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# CH2 P2 - Chem 100 Chapter 2 Units of Measurement...

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Anna Toy-Palmer 1 Chem 100 Chapter 2 Units of Measurement Conversions Multistep conversions Units raised to a power Density

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Anna Toy-Palmer 2 Chem 100 The metric system vs English system Distance, mass, volume, time, temperature What are examples in metric? What are examples in the English system? Metric divides everything in powers of ten Metric prefixes – please memorize them!
Anna Toy-Palmer 3 Chem 100 Prefixes (Please memorize!) tera- 10 12 deci- 10 -1 giga- 10 9 centi- 10 -2 mega- 10 6 milli- 10 -3 Kilo- 10 3 micro- 10 -6 nano- 10 -9 pico- 10 -12 femto- 10 -15 If milli equals 10 -3 , than millimeter = 10 -3 meter How many nanoseconds are in a second?

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Anna Toy-Palmer 4 Chem 100 How do the sizes match up? A person at 6’2” weighing 185 lbs = 1.9 meters tall and 83.9 kgs 190 centimeters tall and 83,900 grams A virus is about 2.8 X 10 -8 meters in diameter = 1.1 X 10 -6 inches (~1/1000000 inches) 28 nanometers in diameter
Anna Toy-Palmer 5 Chem 100 Examples of equivalences between English and metric: 1 inch = 2.54 cm 2.205 lbs = 1 kg 1.057 quarts = 1 liter 1 milliliter (ml) = 1 cm 3

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Anna Toy-Palmer 6 Chem 100 Whenever we convert units, make sure we always keep units with their associated number when writing the equation: do the same mathematical operations to both numbers and units = gallons 3 X gallon miles 10 miles 30 gallon) X gallon miles ( 3) X (10 gallons 3 X gallon miles 10 = =
Anna Toy-Palmer 7 Chem 100 1. To convert, we need to identify the information given and the information sought. 1. We then make a solution map 1. We find the conversion factors needed in the solution map 2. Finally, we carry out the computation Information given Information sought Conversion factors

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Anna Toy-Palmer 8 Chem 100 Conversion examples 1. My height is 68 inches. What is it in centimeters? 1. When we carry out our calculation, we often use a “T- square” to keep our numbers and units organized inches centimeters Conversion factors 2.54 cm = 1 in = 68 in 2.54 cm 1 in 172.72 cm
Anna Toy-Palmer 9 Chem 100 Conversion examples Are we done? Why or Why not?

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Anna Toy-Palmer 10 Chem 100 Conversion examples Are we done? Why or Why not? We need to consider significant figures… What type of mathematical operation are we doing? What is the rule for determining significant figures here? What about rounding? What is the answer in scientific notation? = 68 in 2.54 cm 1 in 172.72 cm
Anna Toy-Palmer 11 Chem 100 Conversion examples The answer would then be: = 68 in 2.54 cm 1 in 172.72 cm = 1.7 X 10 2 cm

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Anna Toy-Palmer 12 Chem 100 Another example Your car’s gas mileage is 15 km/L. What is the gas mileage in miles/gallon? 1 gallon = 3.785 L 1 mile = 1.609 km
Anna Toy-Palmer 13 Chem 100 Your car’s gas mileage is 15 km/L. What is the gas mileage in miles/gallon?

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