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Index
Measured Values• Accuracy of a measurement is
the closeness of the measurement to the true value.• Precision refers to the
reproducibility within a group of measurements.
IndexPrecision, Accuracy and Error
• Accuracy = % Error
= 100 X (Experimental – Actual)
Actual Value
• Precision = % Deviations
= 100 X ( ave. deviation)
mean
deviation = l measured – mean l
Index
Measured Values: Precision
• Significant Digits (means MEASURED)
–ALL Numbers are important
–need Rules to know how many to write
IndexSig Fig Rules 1. 4567
2. 34.989
3. 0.006040
4. 45.0387
5. 2.00
6. 34.900
7. 5000
8. 0.00783
9. 900.
10. 45078
IndexSig Fig Rules : multiply and divide
Answer has same number of significant digits as the number with the least significant digits.
Ex. 12.65 x 42.1 = 532.565
XX
=533
4 3
3
Index
RULES: ADD AND SUBTRACT
decimal place determines the number of digits.
The last COMMON decimal place is the last number you can justify
Ex. 10.13
+ 20.5
30.63X
= 30.6
UV radiation is very energetic and causes your skin to burn. If you are exposed to 1.00 Mole of photons with a wavelength of 305. nm, what amount of energy (in kilojoules per mole) are you being hit by?
Speed of light = 2.998 x 108 m/sPlank’s Constant = 6.626 x 10-34 J s
IndexTypes of Observations and Types of Observations and MeasurementsMeasurements
• We make We make QUALITATIVEQUALITATIVE observations of reactions — observations of reactions — changes in color and physical changes in color and physical state.state.
• We also make We also make QUANTITATIVE QUANTITATIVE MEASUREMENTSMEASUREMENTS, which involve , which involve numbersnumbers..
• Use Use SI unitsSI units — based on the — based on the metric systemmetric system
Index
UNITS OF MEASUREMENTUNITS OF MEASUREMENTUse Use SI unitsSI units — based on the — based on the
metric systemmetric system
Length Length
MassMass
TimeTime
TemperatureTemperature
Meter, mMeter, m
Kilogram, kgKilogram, kg
Seconds, sSeconds, s
Celsius degrees, ˚CCelsius degrees, ˚Ckelvins, Kkelvins, K
Index
Units of LengthUnits of Length• 1 kilometer (km) = ? meters (m)1 kilometer (km) = ? meters (m)
• 1 meter (m) = ? centimeters (cm)1 meter (m) = ? centimeters (cm)
• 1 centimeter (cm) = ? millimeter (mm)1 centimeter (cm) = ? millimeter (mm)
• 1 nanometer (nm) = 1.0 x 101 nanometer (nm) = 1.0 x 10-9-9 meter meter
O—H distance =O—H distance =9.4 x 109.4 x 10-11 -11 mm9.4 x 109.4 x 10-9 -9 cmcm0.094 nm0.094 nm
O—H distance =O—H distance =9.4 x 109.4 x 10-11 -11 mm9.4 x 109.4 x 10-9 -9 cmcm0.094 nm0.094 nm
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