CH 1 notes

# Every derived unit comes from two or more basic units

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- Every derived unit comes from two or more basic units. Density = mass/volume. Mass is basic, volume and density are derived. Volume = length 3 . o Energy = o Pressure = - Density is a conversion factor that can be used to convert mass of a substance to volume of a substance o The density of pure water at 25 o C is 1.00 g/mL. Density of any liquid varies with temperature. o What happens to the density of any liquid as you decrease it’s temperature? o As you increase it’ o How many grams of isopropanol (d = 0.785 g/mL) are in 500 mL? 1.8 Unit Conversions and Dimensional Analysis Conversion Factors: Conversion factors are used to change from one unit to another. Density, molarity, parts per million (ppm), parts per billion (ppb), percentages, LD 50 values are some examples of conversion factors. 1.00 inch = 2.54 cm is another conversion factor (metric to English and vice versa). Study Note: You do not need to memorize conversion factors. HOWEVER you should know how to write all the conversion factors listed above. Use the data on Table 1.9 on page 31 and the table on the back of the textbook cover to solve C.F. problems.

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o A few examples of calculations using conversion factors: 1. A person who weighs 175 pounds is 8% body fat. How many pounds of fat does the person have? 2. The LD 50 (or Lethal Dose that kills 50% of the test population…which are rats) value is a measure of a substance’s toxicity. The lower the value the more toxic the substance. EVERY chemical has an LD 50 value How many mgs of caffeine will kill a 175 pound person if the LD 50 of caffeine is 192 mg/kg?
3. How many liters of olive oil are in 30.0 g if the density of the oil is 0.92 g/mL at 25 °C? (Density is a C.F. used to convert mass to volume for a liquid). **Challenge: How many kg of gasoline are in 40.1 gallons?

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