Scientific Measurements Chapter 3. Objectives Construct and use tables and graphs to interpret data...
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Transcript of Scientific Measurements Chapter 3. Objectives Construct and use tables and graphs to interpret data...
Scientific Measurements
Chapter 3
Objectives
• Construct and use tables and graphs to interpret data sets.
• Solve simple algebraic expressions.• Measure with accuracy and precision (length,
volume, mass, temperature, time, etc.)• Convert within a unit (such as, centimeters to
meters).• Use common prefixes such as milli-, centi-, and
kilo-.• Use scientific notation, where appropriate.• Use ratio and proportion in the solution of
problems.
Objectives
•Determine the correct number of significant figures.•Determine percent error from experimental and accepted values.•Use appropriate metric/standard international (SI) units of measurement for mass (kg); length (m); and time (s).•Use Celsius and Kelvin scales.
Observations
• Qualitative: results in descriptions (Canadian geese)
• Quantitative: results in numerical form (15 Canadian geese)
Accuracy and Precision
• Accuracy: how close measurement is to true value
• Precision:
• how close several measurements are to the same value
• The number of digits in a measurement
Study Buddy Review
• How would you describe the following sets of numbers?
• 68.6, 68.7, 68.9 Goal = 23.0
• 40.02, 40.01, 39.99 Goal = 40.00
• 2.4, 6.0, 7.0 Goal = 4.0
• 0.874, 0.87, 0.86699 Goal= 0.87
Study Buddy Review
• How would you describe the following sets of numbers?
• 68.6, 68.7, 68.9 Goal = 23.0– Precise but inaccurate
• 40.02, 40.01, 39.99 Goal = 40.00– Precise and accurate
• 2.4, 6.0, 7.0 Goal = 4.0– Imprecise and inaccurate
• 0.874, 0.87, 0.86699 Goal= 0.87– Imprecise but accurate
Percent Error• Error: difference between experimental value and
accepted value• Accepted value: true or correct value from
literature• Experimental value: measured value determined
from lab
• % error = accepted value –experimental value x 100
accepted value
Study Buddy Review
• Convert the following to scientific notation:
0.005 g
10,000 m
• Convert the following to standard notation:
1.5 x 10-3 dL
2.2 x 105mL
Study Buddy Review
• Convert the following to scientific notation:
0.005 g 5 x 10-3 g
10,000 m 1 x 104 m
• Convert the following to standard notation:
1.5 x 10-3 dL 0.0015 dL
2.2 x 105mL 220,000 mL
The Metric System
Metric and SI units
• Metric System used in science
• SI System – International System of units based on metric system– Used to standardize quantities between
scientists
Common Units in Chemistry
Quantity it represents
SI unit Common metric unit in Chemistry
Length meter (m) centimeter (cm)
Mass kilogram (kg) gram (g)
Volume m3 (cubic meters)
milliliter (mL)
Temperature Kelvin (K) Celsius (oC)
Mass
• A measure of the quantity of matter; amount of material in an object
• Never changes
(Weight – force due to the pull of gravity on an object)
Volume
• Cube Demo• Cube is 10 cm x 10 cm x 10 cm = 1000 cm3
(also 1 dm x 1 dm x 1 dm or 1 dm3)
• Cube is filled by water in filled 1 liter beaker so1 L = 1000 cm3
1 L = 1000 mL= 1000 cm3 = 1 dm3
*IMPORTANT RELATIONSHIP: 1 cm3 = 1 mL
Temperature
• Temperature: a measure of the average kinetic energy of particles that make up substance
• Use Celsius or Kelvin temperature in chemistry• Kelvin Temperature scale based on absolute zero• Absolute zero or 0 K
– coldest possible temperature– Temperature where motion of particles stops
• A degree in Kelvin is equal in size to a Celsius degree
K = oC + 273
Metric Unit Prefixes
• Used to make the base units larger or smaller so that they are more convenient to use
Prefix Symbol Magnitude Multiple of base unit
Kilo k 103 1,000
Hecto h 102 100
Decka da 101 10
100 1
Deci d 10-1 0.1
Centi c 10-2 0.01
Milli m 10-3 0.001
Conversions to Know
1 Mm = 1 x 106 m
1 km = 1000 m
100 cm = 1 m
1000 mm = 1 m
1 x 106 μm = 1 m
• Can represent meters, grams, liters
Significant Figures
Uncertainty in Measurement• Measurements are uncertain
– Measuring instruments are never completely flawless
– Measuring always involves some estimation
Measuring Practice
Significant Digits/Figures
• All the certain digits in a measured quantity and 1 estimated digit of measurement.
• Rules for determining Significant figures: see handout
Study Buddy Review: Identify S.F.
1. 523.1 mL
2. 0.0025 mg
3. 5002 km
4. 1.8 x 10 6 lbs.
5. 0.090180 L
6. 2000 dogs
7. 2010. cats
8. 14,000.00 carrots
Study Buddy Review: Identify S.F.
1. 523.1 mL 4
2. 0.0025 mg 2
3. 5002 km 4
4. 1.8 x 10 6 lbs. 2
5. 0.090180 L 5
6. 2000 dogs 1
7. 2010. cats 4
8. 14,000.00 carrots 7