Download Chapter 5 - Measurements and Calculations

Measurement Notes
• Chemistry –
the science that deals with the materials of the
universe and the changes these materials undergo
• Qualitative Measurement –
Qualities or observations that can be made about a
substance ex: the substance is a yellow solid
• Quantitative Measurement –
a measurement that consists of a number and a unit
ex: the substance weighs 3.45 grams
Units
•
•
tells what scale or standard is being used to represent the measurement
International System (SI)
•
SI Base Units:
– Length: meter
• measures distance
– Mass: grams
• quantity of matter present in an sample
– Volume: Liter, centimeter cubed
• 1 mL = 1 cm3
• three-dimensional space occupied by a sample
– Temperature: Kelvin, Celsius
• TK = T°C + 273
– Time: second
– Pressure: Pascals
– Energy/Heat: Joules
– Counting Atoms: moles
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…
deci1 _ = 10 d_
centi1 _ = 100 c_
milli1 _ = 1000 m_
micro1 _ = 1 x 106 _
nano1 _ = 1 x 109 n_
pico1 _ = 1 x 1012 p_
*
*
*
*
*
*
( = lowercase Greek Mu)
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
Ex: 200 g
2 1
2 x 102 g
right  use negative exponent
.00314 mL
1 2 3
3.14 x 10-3 mL
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
1
63.2 cm
3.92 x 10-3 m
3 2 1
.00392 m
Element Buddies
Think-Pair-Share
1.
2.
3.
4.
657000000000 m 6.57 x 1011 m
0.000000235 g 2.35 x 10-7 g
9.34 x 102 cL
934 cL
3.35 x 10-3 L 0.00335 L
Uncertainty in Measurement
close
• Accuracy: - How _________
a measurement is
accepted
to the actual or _________value.
To evaluate
know
accuracy you must __________
the true value.
For example, knowing a watch is 5 min
not
fast…The time on the watch is ________
accurate and you know it is not accurate b/c you
adjustment
know the real time and can make an ________.
• Shooting Free Throws - Accuracy can be
measured by how many are __________.
baskets
Precision:
1st Meaning of Precision
set
How close a ____________
of measurements are to the
_________________.
To evaluate precision you must
each other
compare the values of 2 or more _______________
similar
measurements.
• Ex. Measure the temperature of water three times.
Which set of measurements are more precise?
Thermometer 1: 22.3oC, 22.3oC, 22.4oC
Thermometer 2: 24.5oC, 20.1oC, 18.7oC
• Shooting Free Throws - Precision can be measured by
how many _______
Ex.
shots in the same _________.
spot
side
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
right
precise (can ____________
it consistently)
repeat
2nd Meaning of Precision
• Precision can also refer to how __________
a
precise
measurement is (more decimal __________
=
places
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
right
• More numbers to ______________
of decimal,
more precise the measurement is!
Element Buddies
Oh buddy...summarize
Limits to Measurements
• When measuring you should always
______________
the _______
estimate
last digit of your
measurement
• You know what it is definitely _________
than, and
less
you know what it is definitely _______
more than. Divide
those two points into imaginary ___________and
line
estimate how far in between the measurement is.
• Your measurement should be recorded to ONE
DECIMAL BEYOND the ______________marking
calibration
• Your Estimate (or _____________
number) should
uncertain
be the final one on the right.
• If the tool is digital, _________
record the given number
• Measurements always have some degree of
uncertainty (estimation)
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
Ex 2: Measure
the line using
both rulers.
7.56 cm
Element Buddies
What does one digit beyond
the calibration mean?
Significant Figures
All certain numbers plus first uncertain digit
Rules for counting Sig. Figs.
3578 = 4 SF
1. All nonzero numbers are significant.
236 =
3 SF
2. Zeros
a. Leading Zeros – precede all nonzero digits, they NEVER
COUNT
.0025 = 2 SF
.0009 = 1 SF
b. Captive (Trapped) Zeros – fall between two nonzero digits,
they ALWAYS COUNT
6008 = 4 SF
20502 = 5 SF
.00705 = 3 SF
c. Trailing Zeros – come at the end of a number and count IF there
is a DECIMAL POINT
.001500300 = 7 SF
3000 = 1 SF
3000. = 4 SF
2580.0 = 5 SF
3. Exact numbers – have infinite number of sig. figs., they arise from
definitions
1 inch = 2.54 cm, 1 g = 1000 mg
Rounding
If the digit to be removed is –
a. less than 5, the preceding digit stays the same
b. equal or greater than 5, increase the preceding digit
by 1
When rounding off, use ONLY the first number to
the right of the last significant figure
Ex: Round to 3 SF
$ 10,079 = $10,100
0.002978 g = 0.00298 g
0.03296 cm = 0.0330 cm
1000. mL = 1.00 x 103 mL