Measurement Notes. Chemistry – Qualitative Measurement – Quantitative Measurement – the...
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Measurement Notes
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• Chemistry –
• Qualitative Measurement –
• Quantitative Measurement –
the science that deals with the materials of the universe and the changes these materials undergo
Qualities or observations that can be made about a substance ex: the substance is a yellow solid
a measurement that consists of a number and a unitex: the substance weighs 3.45 grams
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Units• tells what scale or standard is being used to represent the measurement• International System (SI)• SI Base Units:
– Length:
• measures distance
– Mass:
• quantity of matter present in an sample
– Volume:
• 1 mL = 1 cm3
• three-dimensional space occupied by a sample
– Temperature:
• TK = T°C + 273
– Time:
– Pressure:
– Energy/Heat:
– Counting Atoms:
meter
grams
Liter, centimeter cubed
Kelvin, Celsius
secondPascals
Joules
moles
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Common prefixes (MEMORIZE)Giga 1 x 109 _ = 1 G_Mega 1 x 106 _ = 1 M_Kilo - 1000 _ = 1 k_Hecto - 100 _ = 1 H_Deka - 10 _ = 1 D_(base) – meter, liter, gram…deci- 1 _ = 10 d_centi- 1 _ = 100 c_milli- 1 _ = 1000 m_micro- 1 _ = 1 x 106 _ ( = lowercase Greek
Mu)nano- 1 _ = 1 x 109 n_pico- 1 _ = 1 x 1012 p_
*
****
*
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Scientific Notation
Expresses a number as a product of a number between 1 and 10 and the appropriate power of 10
If you move the decimal point: left use positive exponent right use negative exponent
Ex: 200 g .00314 mL12
2 x 102 g 3.14 x 10-3 mL
1 2 3
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Converting from Scientific Notation to Ordinary Numbers
move the decimal point:positive exponent => move right
negative exponent => move left
Ex: 6.32 x 101 cm 3.92 x 10-3 m
1
63.2 cm
123
.00392 m
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Element Buddies
Think-Pair-Share
1. 657000000000 m
2. 0.000000235 g
3. 9.34 x 102 cL
4. 3.35 x 10-3 L
6.57 x 1011 m
2.35 x 10-7 g
934 cL0.00335 L
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• Accuracy: - How _________ a measurement is to the actual or _________value. To evaluate accuracy you must __________ the true value. For example, knowing a watch is 5 min fast…The time on the watch is ________ accurate and you know it is not accurate b/c you know the real time and can make an ________.
• Shooting Free Throws - Accuracy can be measured by how many are __________.
Uncertainty in Measurement
closeaccepted
know
not
adjustment
baskets
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Precision: 1st Meaning of PrecisionHow close a ____________ of measurements are to the
_________________. To evaluate precision you must compare the values of 2 or more _______________ measurements.
• Ex. Measure the temperature of water three times. Which set of measurements are more precise?
Thermometer 1: 22.3oC, 22.3oC, 22.4oCThermometer 2: 24.5oC, 20.1oC, 18.7oC
• Shooting Free Throws - Precision can be measured by how many _______ in the same _________. Ex. Consistently hitting the ___________ of the rim and missing. Not accurate b/c not making the shots, but precise b/c results are repeated.
• Science – should be both accurate (___________) and precise (can ____________ it consistently)
seteach other
similar
shots spotside
rightrepeat
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2nd Meaning of Precision• Precision can also refer to how __________ a
measurement is (more decimal __________ = more precise)
Consider mass of sugar in bubble gum– 5 g - wide range of values that it could be! - Could be
between 4.5 g and 5.4 g and rounded to 5 g.– 5.0 g gives you more information – Could be between
4.95 g and 5.04 g.– 5.00 g gives you even more information – Could be
between 4.995 g and 5.004 g
• More numbers to ______________ of decimal, more precise the measurement is!
preciseplaces
right
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Element Buddies
Oh buddy...summarize
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Limits to Measurements• When measuring you should always
______________ the _______ digit of your measurement
• You know what it is definitely _________ than, and you know what it is definitely _______ than. Divide those two points into imaginary ___________and estimate how far in between the measurement is.
• Your measurement should be recorded to ONE DECIMAL BEYOND the ______________marking
• Your Estimate (or _____________ number) should be the final one on the right.
• If the tool is digital, _________ the given number• Measurements always have some degree of
uncertainty (estimation)
estimate last
lessmore
line
calibrationuncertain
record
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Ex 1: Measure the volume of liquid in the graduated cylinder. Remember: The volume is read at the bottom of the liquid curve (called the meniscus).
47.5 mL
7.5 cm
7.56 cm
Ex 2: Measure the line using both rulers.
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Element Buddies
What does one digit beyond the calibration mean?
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Significant FiguresAll certain numbers plus first uncertain digit
Rules for counting Sig. Figs.
3. Exact numbers – have infinite number of sig. figs., they arise from definitions
c. Trailing Zeros – come at the end of a number and count IF there is a DECIMAL POINT
b. Captive (Trapped) Zeros – fall between two nonzero digits, they ALWAYS COUNT
2. Zeros a. Leading Zeros – precede all nonzero digits, they NEVER COUNT
1. All nonzero numbers are significant.3578 = 4 SF
236 = 3 SF
.0025 = 2 SF .0009 = 1 SF
6008 = 4 SF 20502 = 5 SF .00705 = 3 SF
3000 = 1 SF 3000. = 4 SF 2580.0 = 5 SF.001500300 = 7 SF
1 inch = 2.54 cm, 1 g = 1000 mg
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Rounding
If the digit to be removed is –a. less than 5, the preceding digit stays the sameb. equal or greater than 5, increase the preceding digit
by 1When rounding off, use ONLY the first number to
the right of the last significant figure
Ex: Round to 3 SF
$ 10,079
0.002978 g
0.03296 cm
1000. mL
= $10,100
= 0.00298 g
= 0.0330 cm
= 1.00 x 103 mL