CHEMISTRY & SOCIETY

INTRODUCTORY STUDENT NOTES: MEASUREMENT, SCIENTIFIC NOTATION, METRICS, SIGNIFICANT DIGITS, AND DIMENSIONAL ANALYSIS

  1. TWO BASIC TYPES OF MEASUREMENTS
  2. Quantitative - Numerical
  3. Ex. – Mrs. Hutson has a mass of 150 lb…..and rising
  4. Ex. – Mrs. Hutson has an IQ of 185
  5. Qualitative – Non-numerical
  6. Ex. – Mrs. Hutson has brown hair
  1. “CORRECT” MEASUREMENTS
  2. There is Error associated with all measurements
  3. Random – just that, not usually repeated, a fluke
  4. Ex. – Human error – reading a mass of 29g, but recording a mass of 92g
  5. Systematic – occurs with every measurement
  6. Ex.– You make several 20%(w/v) solutions by weighing the solid on an incorrectly calibrated balance
  • Accuracy – Getting the “correct” or “accepted” value
  1. Ex. – Measuring a standard 1 gram mass on a balance and getting a reading of 1.001g
  2. Precision – Getting a repeatable value
  3. Ex. – Measuring the mass of a paperclip on a balance repeatedly and getting readings of 0.874g, 0.875g, and 0.874g.

  1. REPORTING MEASUREMENTS AND CHOOSING PROPER MEASURING DEVICES
  2. Reporting digits
  3. Units - must include with all measurements…WHY?!…
  4. Devices
  5. Mass (grams) – balance
  6. “taring” – setting balance to read “0” before beginning measurement
  7. Length (meter) -
  8. Volume (Liter) – graduated cylinder
  9. The meniscus – bottom of curve observed when viewing a liquid sample in a graduated cylinder
  10. Temperature (C) - Celsius alcohol thermometer
  1. SCIENTIFIC NOTATION
  • Convert the following to expanded forms:

1) 1072) 10-2

3) 1034) 10-5

5) 2.3 x 1046) 0.41 x 10-6

  • Convert the following to scientific notation:

1) 450002) 23.75

3) 0.000704) 0.0123

  1. USING A SCIENTIFIC CALCULATOR

“E” does NOT mean error

Significant Digits

  1. THE METRIC SYSTEM
  2. Le Systeme International d’ Unites
  3. Uses “base” units and prefixes denoting multiples or divisions of 10
  4. Common prefixes: …KHD (b) dcm…refer to metric prefix line handout

Measurement / English unit / metric Base unit
Length
Volume
Mass
Temperature
Energy
  1. PROOF METRIC SYSYEM IS BETTER THAN ENGLISH

Convert 27 meters to Kilometers

Convert 27 inches to miles

Convert 27 liters to milliliters

Convert 27 fluid ounces to gallons

Convert 27 milligrams to Kilograms

Convert 27 ounces to tons

  1. DIMENSIONAL ANALYSIS – A Way to convert between any units – and be guaranteed the correct answer….given that you can set up the problem correctly….and do multiplication and division

THE METHOD / Example 1 / Example 2
This is a structured way of helping you to convert units. With this method, you can easily and automatically convert very complex units if you have the conversion formulas. The method involves the following steps / Convert 6.0 cm to km / Convert 4.17 kg/m2 to g/cm2
1. Write the term to be converted, (both number and unit). If there are no units in denominator, write the term over 1 (does not change anything!) / 6.0 cm
1 / 4.17 kg
m2
2. Write the conversion formula(s) / 100 cm = .00100 km / 1.00 m = 100 cm
1.00 kg = 1000 g
3. Make a fraction of the conversion formula, such that
a) if the unit in step 1 is in the numerator, that same unit in step 3 must be in the denominator.
b) if the unit in step 1 is in the denominator, that same unit in step 3 must be in the numerator.
Since the numerator and denominator are equal, the fraction must equal 1. / .00100 km
100 cm / 1000 g 1.00 m1.00 m
1.00 kg 100 cm 100 cm
4. Multiply the term in step 1 by the fraction in step 3. Since the fraction equals 1, you can multiply by it without changing the size of the term. / 6.0 cm.00100 km
1 100 cm / 4.17 kg1000 g 1.00 m1.00 m
m21.00 kg 100 cm100 cm
5. Cancel units / 6.0 cm.00100 km
1 100 cm / 4.17 kg1000 g 1.00 mx1.00 m
m21.00 kg100 cm100 cm
6. Perform the indicated calculation rounding the answer to the correct number of significant figures. / .000060 km or 6.0 E -5 km / .417 g
cm2

DIMENSIONAL ANALYSIS PRACTICE PROBLEMS 1

______1.What are the correct units for the answer to a problem if the following

series of conversion factor units are used?

quark passel2goober parsec speck

goober speck passel quark2passel

______2. Evaluate the following:

(6.02 x 1023) (9.11 x 10-31) (5.98 x 1024) (3.82 x 108)

(3.92 x 10-16) ( 3 x 108) (8.99 x 1016) ( 1.99 x 1030)

______3. Given the following equivalents, convert 1 fizzle to frizzles.

3 swizzles = 7 twizzles

1 fizzle = 2 drizzles

3 twizzles = 14 sizzles

1 swizzle = 22 frizzles

8 drizzles = 5 sizzles

______4. Jules Verne wrote a book called Twenty Thousand Leagues Under the Sea.

Using the conversion factors listed below, convert 20,000 leagues to inches.

12 in = 1 ft

3 ft = 1 yd

1 fathom = 2 yards

1 statute mile = 5280 ft

1 nautical mile = 6080 ft

1 league = 3 nautical miles

Directions(5-8): Use your table of conversion factors to make the following conversions:

______5. Convert 6.35 miles to kilometers.

______6. Convert 60 inches to meters.

______7. Convert 60 mi/hr to in/min

______8. At $1.35 per gallon, how much will it cost to buy 225 liters of Amoco

Ultimate gasoline?