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Chemistry

Chemistry. The Metric System and SI Units. Why, Why, Why. The US is the only country in the World that does not use the Metric System, even though it is the official system adopted by Congress. Science does not use the English system because there is no definable standard.

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Chemistry

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  1. Chemistry The Metric System and SI Units

  2. Why, Why, Why • The US is the only country in the World that does not use the Metric System, even though it is the official system adopted by Congress. • Science does not use the English system because there is no definable standard. • This system the US uses is based on superstition, body parts and changeable parts of nature.

  3. Would You Like Some Examples? • The foot = the size of your foot

  4. More Examples? • The Yard was the distance from the end of your nose to the tip of your index finger. The inch was three corn kernels side by side, a rod was the length of 16 men’s feet. A cubit was the distance from the elbow to the end of the hand. And so on, and so on, and scoobie doubie dooa.

  5. The Standard • In order for the Scientific Community to communicate it was necessary to develop a standard unit of measurement. Something that was definable and more reliable than body parts. Also it was important that the standard was able to be reproduced from the definition.

  6. Mother Earth • It was decided that the earth would be the standard. 230 By measuring the distance between the equator and the north was a good place to start. This was done by trangulation. If distance was divided by 10 million, each segment would be exactly one Meter. The Earth tilts at an angle of 230

  7. Let’s Lay It On The Line Std Unit (m) Meter (l) Liter (g) Gram • p n μ m c d • da h k M G T • p pico m mili da deka M mega • n nano c enti h hecto G giga • μ micro d deci k kilo T tara Divisions Multiples 101 102 103 106 109 1012 1012 109 106 103 102 101 Divisions are below the line and Multiples are above the line. No negative exponents.

  8. The Method • The Unit Factor Method. Step 1. Put the known value on the left and the unknown on the right Convert 6,980 milligrams to kilograms Step 2. Look for the standard unit. If it is not there put it in the middle. 6,980 mg kg g

  9. Continue Step 3. Draw a line under the UNITS • 6,980 mg kg Step 4. Copy the unit on the LEFT under the unit on the RIGHT. Separate with a line. g 1.00 1.00 = 6.98 x 10-3kg mg g 1.00 x103 1.00 x103 Step 5. Make the units equal from the line. Put a 1.00 by the larger unit and the exponent by the smaller number. Step 6. Cancel units and calculate.

  10. Don’t Ya Just Luv Conversions Converting Metric units to English Units Converting English units to metric Units

  11. Conversion Factors • You Only Need Six Conversions Mass: 454 g = 1.00 Lbs 1.00 kg = 2.20 Lbs Length 2.54 cm = 1.00 in 1.00 mi = 1.61 km Volume: 1.06 l = 1.00 qt 1.00 ft3 = 2.84 x 104 cm3

  12. English to Metric orMetric to English • Follow the same 6 steps as in metric to metric conversions. • 1. The known is on the LEFT and the unknown is on the RIGHT. • 345 m to ft. is an example.

  13. Apply the Method • 345 m ft • 2. Look for the conversion UNITS under what is being measured. • Length? Mass? Volume? Etc. • I choose cm to inches which is the closest to the units in the problem. Place the English next to the English and the metric next to the metric. • 345 m cm in ft

  14. Continue the Method • 345 m cm in ft 102 1.00 1.00 m cm 12.0 in 1.00 2.54 = 1.13 x 103 ft 3. Draw an line under the units. 4. Copy the right unit under the left unit. 5. Make them equal from the number line or the conversion chart. 6. Cancel units and calculate.

  15. Be Fruitful and Multiply • Multiple Conversions: • Use the same six steps of the method. • Apply the method to convert units that measure the same thing. • Mass to Mass grams to Lbs • Volume to Volume cm3 to ft3 • Length to Length miles to Km • Time to Time Seconds to hr

  16. Multiple Conversion – Type One • Convert 123 cm/s to m/s • This problem the time units are the same and do not need to be changed. • Follow the Steps for the cm to m conversion. • Leave seconds as seconds • 123 cm m 1.00 cm 1.O0 x 102 = 1.23 m/s 1.00s

  17. The Ultimate • Convert 123 mi/hr to m/s. • Step 1 through Step 6 • 123 mi m km 1.61 103 km 1.00 mi 1.00 = 5.50 x 101 m/s 1.00 hr 3600 s 1.00 hr

  18. A True Conversion • How many grams/cm2 are in 12.3 lbs/ft2? • 12.3 lbs g • 2.54 cm = 1.00 in • 30.5 cm = 1.00 ft • 9.30 x 102 cm2 = 1.00 ft2 454 1.00 lbs = 6.00 g/cm2 cm2 1.00 ft2 9.30 x 102 1.00 ft2 ( ) 12 12 ( ) 2 2 ( ) ( )

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