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Chapter 3 Scientific Measurement

- A. Types of Measurements
- Quantitative number and unit
- counting or measuring
- Qualitative observations using the 5 senses
- - distinctive characteristics

determine the specific make-up of a substance - In chemistry, we use both quantitative and

qualitative types of analysis

- B. Scientific Notation
- Used to shorten really long numbers
- General form _ . _ x 10exp
- Positive exponent gt 1 (greater than)
- Negative exponent lt 1 (less than)
- Only when there is a negative sign in front of

the first set of numbers is the number negative

(a neg. exp. does not mean a neg. !) - ex. 3.6 x 103 is a pos. gt 1
- 3.6 x 10-3 is a pos. lt 1 (but gt 0)
- -3.6 x 103 is a neg.

- Why use scientific notation?
- ex. 3.6 x 103 3600. (decimal moves right)
- 3.6 x 10-3 .0036 (decimal moves left)
- -3.6 x 103 -3600
- 6.02 x 1023 whoa mama!
- 602000000000000000000000 (21 0s)

- Practice these
- ex. 3.17 x 107
- 6.1 x 10-5
- 1800000
- 0.000482

31700000 0.000061 1.8 x 106 4.82 x 10-4

- How do you plug scientific notation into the

calculator for calculations? - Hit open parenthesis button (
- Type in the decimal part _ . _
- Hit the exponent button EXP or EE (this

button means x 10) - no need to type x 10 - Type in the exponent part
- Hit the close parenthesis button )
- Hit the operations button (, -, x, )

- How to read the answer on the calculator?
- Enter 3.62171 x 10-14 into the calculator
- 3.62171E-14 3.6 x 10-14
- 3.62171 x10-14 3.6 x 10-14
- 3.62171 -14 3.6 x 10-14

- Practice these
- ex. (3.0 x 104) x (2.0 x 102)
- (8.0 x 109) (2.0 x 104)
- (3.6 x 1013) / (1.4 x 10-3)
- (7.481 x 10-5) x (4.2 x 10-2)

6.0 x 106 4.0 x 105 2.6 x 1016 3.1 x 10-6

- C. Significant Figures
- Significant figures (sig figs) are the

important numbers in a - Rules for rounding answers
- Answers should be reported according to the least

amount of decimal places in the data - ex. (7.481 x 10-5) x (4.2 x 10-2) 3.1 x 10-6
- 3 decimals 1 decimal 1 decimal

- Rounding to a decimal place
- When you have more numbers in your calculator as

an answer and you have to round to the correct

number of sig figs - Look at the decimal place to the right of the

last sig fig that you need to report - If the number is 5-9, you round up
- If the number is 0-4, you round down (last number

stays the same)

ex. 726.835 to 2 decimals 24.8514 to 3

decimals

726.84 24.851

- Rules to determine sig figs from numbers
- Every non-zero digit in a measurement is

significant (ex. 24.7, 0.743, 714) - Zeros between non-zeros are significant (ex.

7003, 40.79, 1.503) - Zeros to the left of non-zeros are not

significant (ex. 0.0071, 0.42, 0.000099)

- Rules (cont.)
- Zeros at the end of a number (right of the

decimal) are significant (ex. 43.00, 1.010) - Zeros at the end of a number (left of the

understood not written decimal) are not

significant (ex. 300, 7000, 27210) - Zeros at the end of a number (left of the

decimal) are significant (ex. 300., 27210.)

- Sig figs in measurements
- Write down all known numbers, plus one extra

number that is estimated - ex.

(a) 0.6 m 60 cm 600 mm

(b) 0.61 m 61 cm 610 mm

(c) 0.607 m 60.7 cm 607 mm

- Precision vs. accuracy
- Precision how close measurements are to

each other (repeated trials) - Accuracy how close measurements are to

the actual or accepted value - ex.

Precise but not accurate

Both precise and accurate

Not accurate and not precise

- Percent error
- Experimental (e) your value obtained
- Accepted (a) the correct or true value
- absolute value (make value positive)
- Formula accepted experimental x 100
- accepted
- Shorthand a e x 100
- a
- Answer _____
- (use correct of sig figs)

- D. Types Of Measurements
- SI units
- SI - International System of Units (standard

measurements in science) - Uses the metric system (based on 10)
- Time seconds (s)
- Temperature Kelvin (K)
- Length meter (m)
- Mass kilogram (kg)
- Volume cubic meter (m3)

- Prefixes used
- Prefixes go in front of the unit symbol and are

always lower case - Kilo (k) 1000 or 103 (1000 times larger)
- Deci (d) 0.1 or 10-1 (10 times smaller)
- Centi (c) 0.01 or 10-2 (100 times smaller)
- Milli (m) 0.001 or 10-3 (1000 times smaller)

- Length
- Units
- Meter (m) SI unit
- Centimeter (cm)
- Millimeter (mm)
- Use a meter stick or ruler (cm side only)
- Conversions
- 1 m 100 cm 1000 mm
- 1 cm 10 mm

- Mass
- Weight the force on an object by gravity
- is different on the earth and moon
- Mass the amount of matter (stuff) in an

object - is the same with or without gravity

(the same on the earth and moon) - Use a digital balance in lab

- Mass (cont.)
- Units
- Kilogram (kg) SI unit
- Gram (g)
- Milligram (mg)
- Conversions
- 1 kg 1000 g
- 1 g 1000 mg

- Volume
- Regular shaped solid
- Measure using a meter stick or a cm ruler
- V L x W x H
- Units cm x cm x cm cm3
- Irregular shaped solid
- Measure using the displacement method (use

graduated cylinder and water) - Units mL or L

- Volume (cont.)
- Liquid
- Measure using a graduated cylinder at the

meniscus (the bottom of the curve) - Units mL or L
- Units
- Liter (L)
- Milliliter (mL)
- Cubic centimeter (cm3) or (cc)
- Conversions
- 1 L 1000 mL
- 1 mL 1 cm3 1 cc

- Density
- Density mass / volume
- D m / V
- Mass is in grams
- Volume is either in cm3 or mL
- Density of water (pure H2O) 1.0 g/mL
- 1 g H2O 1 mL H2O
- Object floats in H2O if D lt 1.0 g/mL
- Object sinks in H2O if D gt 1.0 g/mL

- Temperature
- Scales
- Fahrenheit (?F)
- Celsius (?C)
- Kelvin (K) SI unit
- Only Celsius (used most of the time, especially

in lab) and Kelvin are used! - Use a thermometer in lab