Transcript Ch. 3 Scientific Measurement

Ch. 3 Scientific Measurement
3.1 The Importance of
Measurement
Qualitative &Quantitative
Measurements
qualitative
 descriptive
 big, small, hard, soft
quantitative
 numbers & units
 numeric data - 100, 50g
Scientific Notation
 in sci. not. A # is written as the product of 2 #s
 a coefficient & a 10 to a power
 6.02 * 1023
 allows uniform way to represent #s
 easier for really big & really small #s
 numbers > 10 exponent is +
 numbers < 10 exponent is –
Multiplication in Sci Note
Multiply the coefficients & add exponents
(3.0 * 103) * (2.0 * 102) = 6.0 * 105
Division in Sci Note
Divide the coefficients & subtract the
exponents
(9.0 * 103) / (3.0 * 101) = 3.0 * 102
Addition & Subtraction in Sci Note
 Make exponents the same
 This aligns the decimal points
 Then add or subtract coefficients
 (6.02 * 1023) + (1.00 * 1025) =
 6.02 * 1023 + 100.00 * 1025
3.2 Uncertainty in
Measurements p. 54
Accuracy, Precision
 Accuracy – how close to actual or true value
 Precision – how close a series of
measurements are to each other
 Ex. Dart board
 Bull’s eye – accurate & precise
 All same spot not near bull’s eye – precise
 1 bull’s eye & 2 others – 1 accurate & poor precision
Error
Accepted value – correct value
Experimental value – measured value
Error = experimental value – accepted
value
Percent error
 Use absolute value of error to make +
Significant Figures in
Measurements
include all known (measured) figures + 1
estimated
Allow common language for
communicating numbers
Rules for Sig Fig
 Every non-zero digit is sig – 123.5
 Zeroes between non-zero digits are sig – 1002
 Zeroes at the end of a # to right of decimal are sig
– 123.500
 Leftmost zeroes in front of non-zero # are not sig –
0.005
 Rightmost zeroes @ end to left of understood
decimal are not sig – 1200
Unlimited Sig Figures
Counting
 If it’s an exact count
 Ex. Count 20 students in class
Exactly Defined Quantities
 60 minutes in 1 hour
 24 hours in 1 day
Significant Figures in Calculations
calculated figure cannot be more precise
than measurements from which it’s
calculated
round answer to correct sig fig
Rounding Sig Fig
 if digit immediately to the right of the last sig digit
is less than 5, all numbers including it (to the right)
are dropped & the digit stays the same
 if the digit to right is  5 then round the last sig fig
up to 1
 option
 if the digit to the right = 5 and not followed by a zero
then if odd, round up or if even, do not round
 different books have different opinions
 idea behind this option is to give you equal weight
Addition & Subtraction
Round to same # of decimal places as the
measurements w/ least (not digits)
Multiplication & Division
 Round to same # of sig fig as the measurement
w/ the least
3.3 International System of
Units
Units of Measurement – p.63 Table 3.1
Common Prefixes – p.64 Table 3.2
Metric Length – p.64 Table 3.3
Metric Volume – p.65 Table 3.4
Units of Length
Metric System
 Base of 10
 Convert easily
SI – International System of Units
Basic unit = meter
linear measure
Units of Volume
 volume – space occupied by a sample of
matter
 basic unit = cubic meter (m3)
 volumetric glassware (* more accurate)
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*pipet or buret
*volumetric flask
graduated cylinder
beaker
Erlenmeyer flask
Units of Mass
 astronaut on moon is 6x < than on earth
 force of gravity 6x > on earth than on moon
 weight = force that measures the pull on a
given mass by gravity
 mass = measure of quantity of matter
 basic SI unit = 1 kg
 1 kg = 1 L of H20(l) @ 4C
 a cube of H2O @ 4C measuring 10cm on each side = a
volume of 1L
 mass of 1 cm3 H2O @ 4C = 1g
3.4 Density p. 68
Determining Density
ratio of mass to volume
density = mass / volume
units = g/cm3
Density Cont.
less dense floats on more dense
as temp increases
 volume increases (most substances)
 mass remains same
 density decreases
Specific Gravity
 comparison of D of a substance w/ D of a
reference substance
 H2O @ 4C = 1 g/cm3 (Density reference)
 Specific gravity (s.g.) = Density of substance
(g/cm3)
 Density of H2O (g/cm3)