Measurement and Significant Figures
I. Equipment (general introduction)
- Measuring liquids (grad.cylinder, pipette, buret, volumetric flask)
- Measuring mass (triple beam balance, electronic scale)
- Purpose vessels (E-flask, beaker, funnel, Bunsen burner)
II. Metric system
A. measured and derived units
B. prefixes (equalities) Table C reference tables.
III. Measurement
A. length
B. volume
C. mass
D. temperature
IV. Scientific Notation
A. Writing numbers
V. Significant Figures
A. Determination
B. In calculations
VI. Dimensional Analysis
VII. Density
VIII. % error calculations
- Equipment
II.Metric System
A.measured and derived units
measured
lengthm
massg
volume l
times
temp K
energyJ
amount of substance mol
derived
area = cm2
volume =cm3
density = g/cm3
B.prefixes (equalities)
III.Measurement
Chief Concept: You are obligated to estimate one digit past what you can measure!
A.length
B.volume
C.mass
D.temperature
IV.Scientific Notation
A.writing numbers
Many numbers in chemistry are too large or too small to be easily understood.
1.Examples:
mass of a proton 1.672621777(74)?10-27kg
average human body contains 7.00x10 27atoms
2.Technique
Correct scientific notation begins with 1 digit, a decimal point, all significant figures x 10 some power.
ex: 3031 = 3.031x103
.00000404 = 4.04x10-6
100,000 = 1x105
17 =
.0003 =
15,045 =
Remember: moving the decimal to the left = positive exponent decimal to the right = negative exponent
V.Significant Figures
A.Terminology
1.non-zero digits
2.embedded zeros - zeros between non zero digits
3.trailing zeros - zeros listed after non-zero digits
4.leading zeros - zeros placed in front of non-zero digits
B.determination of
1.Examples:
# sig figs
a) 45.73
b) 8.4164
c) 1302
d) 400.3
e) 400 1
e) 3007.4
f) 6000.15
g) 0.0051
h) 0.0802
i) 6.4004
j) 200.0006
2.*THE RULE: all numbers are significant except for
a.leading zeros
b. trailing zeros without a decimal.
C.in calculations
1.Addition/ subtraction
Rule: The answer is limited to the least precise (fewest decimal places) number in the question.
ex. 200.62483.20
7.4966 - 64.605
+ 43.314 418.595
251.4306 418.60
2.multiplication / division
Rule: Multiplication / Division
The product or quotient is limited to the same number of sig figs as the least in the question.
ex. 76.3
x 320
24.416
VI.Dimensional Analysis
A.Uses and Technique
B.Examples:
Practice Problems:
note: The problems begin with very easy problems and become progressively harder.
1. Convert 3.42 g into kilograms
2. How many inches are in 2.0 miles?
3. Dr. Ott can run a marathon (26.22 miles) in 2.925 hours. What is his average speed in m/s?
4. If I average driving 60.0 miles/hour when traveling (including stops and sleeping) how far can I get in 3.5 days?
VII.Density
A.Density is defined as how tightly packed the atoms in a substance are. With regard to elements, the metal osmium is the densest, nearly twice as dense as lead. Each element has a unique value for density and therefore it is a way unknown elements can be identified.
B.Examples:
1. Calculate the density for the following object. If you know that the object has a mass of 20. grams and the volume is 10. ml.
2. Calculate the volume for the following object If you know that the object has a mass of 21.0 grams and the density is 12.0 g/ml.
3. Calculate the mass for the following object. If you know that the object has a density of 20.0 g/ml and the volume is 5.00 ml.
4. Calculate the density of a liquid in a beaker. The beaker has a mass of 15 grams when empty. The beaker plus an unknown liquid has a mass of 50. grams. What is the density of the liquid if its volume is 10.mL?
5. What is the volume in mL of 10.5 g of Br2?
6. What is the mass (in kg) of 3.2 L of Br2?
VIII.% error calculations
1.Joshua uses his thermometer and finds the boiling point of ethyl alcohol to be 75oC.He looks in a reference book and finds that the actual boiling point of ethyl alcohol is 80oC. What is his percent error?
2. An object has a mass of 35.0 grams. On Anthony’s balance, it weighs 34.85grams.What is the percent error of his balance?