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CHEMISTRY IS LARGELY A QUANTITATIVE SCIENCE

CHEMISTRY IS LARGELY A QUANTITATIVE SCIENCE . The recording of a quantitative observation (some kind of numerical value) in experiments involves ACCURACY and PRECISION. These are not the same thing.

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CHEMISTRY IS LARGELY A QUANTITATIVE SCIENCE

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  1. CHEMISTRY IS LARGELY A QUANTITATIVE SCIENCE The recording of a quantitative observation (some kind of numerical value) in experiments involves ACCURACY and PRECISION. These are not the same thing. It is necessary to record data with both the appropriate number of SIGNIFICANT DIGITS and the CORRECT UNITS.

  2. Systems of measurements • A. English System - what the United States uses today derived from the 'Kings" feet (Old England) • Units • 1 foot (“big feet") • 1 inch (knuckle) • 1 yard (King Henry I - nose to thumb)

  3. System Internationale (S.I.) • The creation of the decimal Metric System at the time of the French Revolution and the creation of two platinum standards representing the meter and the kilogram was the first step in the development of the present International System of Units.

  4. Prefixes

  5. The seven fundamental units of measurement

  6. Length • Length is a fundamental unit. In the metric system, the meter is a the standard unit for measuring length. It is a little longer than a yard. • The standard unit of metric length is kept in Paris. It is equal to 39.37 inches. Since the meter is equal to 100 centimeters (cm), then 1 inch is equal to 2.54 cm. • Comparisons: • centimeter - width of your fingernail • kilometer - 0.60 miles • millimeter - thickness of a dime

  7. Mass • Mass is a fundamental unit; it is a measure of the quantity of matter present. Although we typically use the words mass and weight interchangeably in normal conversation, mass and weight actually have different meanings. Weight includes the effect of gravity on mass. In a space capsule, your weight would be zero (absence of gravity) but your mass would be the same value as it was on earth. The standard unit of mass is the kilogram (kg). • Conversions factors: • 1 pound = 454 g • 2.2 pounds (lb) = 1 kilogram (kg) • 1 gram (g) = 1000 milligrams (mg) or 1 mg = 0.001 g • 1 kilogram (kg) = 1000 grams (g) or 1 g = 0.001 kg

  8. Volume • – volume is a derived unit (using length units). It is a measure of space. In simple terms, it is a measure of three (3) length units in three dimensions (breadth, length and width). The standard unit of measurement is the meter cubed (m3) or the centimeter cubed (cm3). • In chemistry, volume is typically measured for a liquid. The standard unit of measurement for a liquid is the liter (L). The liter is similar to a quart in the English system. • Conversion factors: • 1 liter (L) = 1.06 quarts (qt) • 1 quart (qt) = 0.946 liters (L) • 1 liter (L) = 1000 milliliters (ml) or • 1 milliliter (ml) = 0.001 liter (L) • 1 milliliter (ml) = 20 drops • At room temperature, 1 milliliter (ml) of water = 1 cm3. (or 1 CC)

  9. Temperature • A fundamental unit. There are three(3) temperature scales BPH20 FPH2O Difference (1) Fahrenheit (F) 212° 32° 180° (2) Celsius (centigrade) (C) 100° 0° 100° (3) Kelvin (K) 373 273 100 • Conversion: Kelvin to Celsius (K -> C) C = K - 273 Celsius to Kelvin (C -> K) K = C + 273 Celsius to Fahrenheit (C -> F) i multiply C x 9/5 ii Add C x 9/5 + 32 Fahrenheit to Celsius (F -> C) i add F - 32 ii multiply (F - 32) x 5/9

  10. Derived units • Derived units can be resolved into combinations of fundamental units • Area and volume involve only the units of length • Most involve combinations of different units

  11. Dimensions • It is important to keep track of the dimensions in derived units. • All the more when making conversions: • 1 cm = 10 mm • 1 cm2 = 100 mm2 • 1 cm3 = 1,000 mm3

  12. Density • Mass divided by volume • Units are: • g/cm3(solid) • g/mL (liquid) • g/m3 (gas)

  13. Density and temperature • In most cases, the density of a substance decreases with temperature. (Why is that?) • Water provides a critical exception to the rule

  14. Conversion factors • Making conversions between different units is very important • Always keep track of the units • Make use of unit factors • There are 1000 mg in 1 g (conversion factor) • 1000 mg/1 g = 1; 1 g/1000 mg = 1 (unit factors) • There are two unit factors for any conversion

  15. Unit factors at work • How many grams are there in 2680 mg of sucrose? • We know there are 1 000 mg in 1 g • 1 g/1000 mg = 1 (unit factor) • ? g = amount in mg x unit factor • ? g = 2680 mg x 1 g/1000 mg = 2.680 g • Unit factor hasvalue of 1 – no change in value • Application of unit factor causes old units to cancel • Never forget to show units of any measurement – unless it is a unit-less quantity

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