A. Measurement

1
A. Measurement
Measurements Data that describe QUANTITATIVE
and QUALITATIVE characteristics of matter
2
Measurement Chemistry Example
Quantitative Added 25.0 mL of a solution
containing 1.0 g of potassium iodide (KI) to
100.0 mL of a test solution thought to contain
lead cations The precipitate (PbI2) was filtered
out, dried, and its mass was 3.7 g. Assuming an
excess of KI, this means the test solution
contains 1.7 g lead (Pb) cations
Qualitative The addition of potassium iodide
(KI) to the test solution caused a YELLOW
precipitate to form. This suggests the
presence of lead (Pb) cations in the test
solution
3
B.Units

• A UNIT tells what was measured

metersnow we know what and how much
5.27 .. WHAT?
DERIVED UNITS.these come from multiplying or
dividing base units
4
Derived units

• Remember that base units combined to form derived
  units provide another property description or
  characteristic
• What I mean is. Suppose I
• Square a length unit Now I express area
• Cube a length unit Now I express volume
• Divide mass by volume Now I express density

http//www.seed.slb.com/en/scictr/watch/gashydrate
s/images/cube2.jpg
From gizmos
5
SI Units
International System of Units (SI)
Prefix Unit Abbreviation Exponential Factor Meaning
mega M 106 1,000,000 times
kilo k 103 1,000 times
centi c 10-2 1/100th
milli m 10-3 1/1,000th
micro ? 10-6 1/1,000,000th
6
Important Base and Derived units
7
C. Using Scientific Measurements
Precision and Accuracy
Precise Accurate
Precise Not Accurate
Not Precise Not Accurate
Not Precise Accurate
There are methods to quantify HOW accurate and
HOW precise
8
ERROR
Absolute value
Average experimental value
error true value expt value x 100
true value
AKA accepted value
error is a method of expressing the accuracy of
the measurement By itself, it doesnt say
anything about the precision of multiple trials
Activity shoot darts, determine precision,
accuracy, and error