CHEMISTRY & SOCIETY



CHEMISTRY & SOCIETY

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

I. TWO BASIC TYPES OF MEASUREMENTS

▪ Quantitative - Numerical

i. Ex. – Mrs. Hutson has a mass of 150 lb…..and rising

ii. Ex. – Mrs. Hutson has an IQ of 185

▪ Qualitative – Non-numerical

i. Ex. – Mrs. Hutson has brown hair

II. “CORRECT” MEASUREMENTS

▪ There is Error associated with all measurements

i. Random – just that, not usually repeated, a fluke

1. Ex. – Human error – reading a mass of 29g, but recording a mass of 92g

ii. Systematic – occurs with every measurement

1. 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

▪ Precision – Getting a repeatable value

1. Ex. – Measuring the mass of a paperclip on a balance repeatedly and getting readings of 0.874g, 0.875g, and 0.874g.

III. REPORTING MEASUREMENTS AND CHOOSING PROPER MEASURING DEVICES

▪ Reporting digits

▪ Units - must include with all measurements…WHY?!…

▪ Devices

i. Mass (grams) – balance

1. “taring” – setting balance to read “0” before beginning measurement

ii. Length (meter) -

iii. Volume (Liter) – graduated cylinder

1. The meniscus – bottom of curve observed when viewing a liquid sample in a graduated cylinder

iv. Temperature (C) - Celsius alcohol thermometer

IV. SCIENTIFIC NOTATION

▪

▪

▪ Convert the following to expanded forms:

1) 107 2) 10-2

3) 103 4) 10-5

5) 2.3 x 104 6) 0.41 x 10-6

▪ Convert the following to scientific notation:

1) 45000 2) 23.75

3) 0.00070 4) 0.0123

V. USING A SCIENTIFIC CALCULATOR

❑ “E” does NOT mean error

❑ Significant Digits

VI. THE METRIC SYSTEM

▪ Le Systeme International d’ Unites

▪ Uses “base” units and prefixes denoting multiples or divisions of 10

▪ Common prefixes: …KHD (b) dcm… refer to metric prefix line handout

|Measurement |English unit |metric Base unit |

|Length | | |

|Volume | | |

|Mass | | |

|Temperature | | |

|Energy | | |

VII. 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

VIII. 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 |Convert 6.0 cm to km |Convert 4.17 kg/m2 to g/cm2 |

|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 | | |

|1. Write the term to be converted, (both number and |6.0 cm |4.17 kg |

|unit). If there are no units in denominator, write the |1 |  m2 |

|term over 1 (does not change anything!) | | |

|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 |.00100 km |1000 g    1.00 m    1.00 m |

|a) if the unit in step 1 is in the numerator, that same |100 cm |1.00 kg   100 cm    100 cm                |

|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. | | |

|4. Multiply the term in step 1 by the fraction in step |6.0 cm .00100 km |4.17 kg   1000 g   1.00 m   1.00 m |

|3. Since the fraction equals 1, you can multiply by it |  1 100 cm |         m2  1.00 kg  100 cm  100 cm |

|without changing the size of the term. | | |

|5. Cancel units |6.0 cm .00100 km |4.17 kg    1000 g   1.00 mx 1.00 m |

| |      1        100 cm |        m2   1.00 kg   100 cm  100 cm |

|6. Perform the indicated calculation rounding the answer|.000060 km or 6.0 E -5 km |.417 g |

|to the correct number of significant figures. | |     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 passel2 goober parsec speck

goober speck passel quark2 passel

__________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?

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