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QUANTITATIVE : How much? One subject 2 tusks Weight (or mass). QUALITATIVE : What is it? Gray Elephant White tusks Wide and large. www.clipartof.com. Measurements : Data that describe QUANTITATIVE and QUALITATIVE characteristics of matter. A. Measurement. - PowerPoint PPT Presentation
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A. Measurement
Measurements:Data that describe QUANTITATIVE and QUALITATIVE characteristics of matter
www.clipartof.com
QUANTITATIVE: How much?
• One subject
• 2 tusks
• Weight (or mass)
QUALITATIVE: What is it?
• Gray Elephant
• White tusks
• Wide and large
Measurement: Chemistry Example
Quantitative
Added 25.0 mL ofa solution containing1.0 g of potassium iodide (KI)to 100.0 mL of a test solutionthought 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 potassiumiodide (KI) to the test solutioncaused a YELLOW precipitateto form.
This suggests the presenceof lead (Pb) cations in the test solution
B.Units
• A UNIT tells what was measured
5.27 …….. WHAT?
meters…now we know what and how much
DERIVED UNITS….these come from multiplying or dividingbase units
Example: I drove 3.2 kilometers from home to work today. It took about 722 seconds to arrive.
3.2 km 722 s
= 0.0044 km s
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/gashydrates/images/cube2.jpg
SI Units
Quantity Symbol Unit Name Unit Abbreviation
length l meter m
mass m kilogram kg
time t second s
temperature T Kelvin K
amount of substance n mole mol
current I ampere amp
luminous intensity Iv candela cd
International System of Units (SI)
Prefix Unit Abbreviati
on
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
Important Base and Derived units
Quantity Definition Common Unit(s) length
amount of linear space mm, cm, m, km
mass
amount of matter mg, g, kg
volume
amount of 3-dimensional space mL, cm3, L
density
mass/ volume g/ mL, g/ cm3, g/ L
temperature
average KE of particles C, K
amount
# of particles mol
pressure
force/ area mm Hg, atm, kPa
concentration
amount/ volume or mass/ volume %, M, m
C. Using Scientific Measurements
Precision and Accuracy
PreciseAccurate
PreciseNot Accurate
Not PreciseNot Accurate
Not PreciseAccurate
There are methods to quantify HOW accurate and HOW precise…
II. Measurements and the Characteristics of Numbers
• Significant Figures-digits with experimental meaning. All digits in a measurement are CERTAIN except the last which is understood to be UNCERTAIN or estimated
57.2574
CERTAIN UNCERTAIN
• Rules
0.00100050300
•Zeros that are place holders are NOTsignificant
• Zeros between non-zero digits AREsignificant
• Zeros at the END of a number are significantIF the number has a decimal point
ZEROS
100050300
Zeros NOTsignificant
Numbers: Rounding and Reporting
78,200.9834
Round to 3 significant digits: 78,200
Round to 5 significant digits: 78,201
Round to 1 significant digits: 80,000
Round to 7 significant digits: 78,200.98
Reporting:
This burette is marked in 0.1 mLincrements.
How many significant digits AFTERThe decimal point would you report?
Concave meniscus
Math Operations with Sig Figs
Multiplication and Division of numbers:The number of SIG FIGS in an answer should be reported with the least number of significant digits in any one of the numbers being multiplied, divided etc.
37.2872x 45.3________ 1690 (Ouch! Seems harsh but those 6 SIG FIGS in the first number were ”killed” by the 3 SIG FIGS in the second number)
Addition and Subtraction of numbers:The number of decimal places (not SIG FIGS ) in the answer should be thesame as the least number of decimal places in any of the numbers being added or subtracted. 23.3456+3.3_______26.6 (3 SIG FIGS total but only 1 behind the decimal place)
% ERROR
% error = | true value – expt value| x 100%
true value
AKA “accepted value”
Average experimental valueAbsolute value
% error is a method of expressing the accuracy of the measurement
By itself, it doesn’t say anything about the precision of multiple trials
Scientific Notation
• Why?– Would you rather write this: 6.023 x 1023
– Or THIS: 602,300,000,000,000,000,000,000
• FORMAT
M x 10n
1 ≤ M < 10AND with the propernumber of significantdigits; can be (-) or (+)
Base 10 number
Exponent is a whole numberinteger; can be (-) or (+)
Proportions-Relationship of Variables
A is directly proportional to B
A Bwhen
A = kB
A is inversely proportional to C
A Cwhen
A Bwhen
A Cwhen
A
B
A
C
A = k/C
Quotient of A andB is constant
Product of A andC is constant