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Notification of Reports
▪ Significant Figures (s.f.)⚫ Significant figures in measurements
⚫ Significant figures in calculations
⚫ Examples in reports
▪ Reports⚫ Prelab Report:
• Principles
• Chemicals
• Procedures
⚫ Error and others
2021/02/18
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Certain to 26 oC
read an uncertain digit
Temp.: 26.2 oC
Certain to 6.2
read an uncertain digit
V: 6.26 mL
Records of Measurement:Significant Figure with Unit
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Take all the digits
on display
Temp.: 27.8 oC
Take all the digits
on display
Wt.: 0.20 g
Records of Measurement:Significant Figure with Unit
Significant Figures in Measurements
▪ Significant Figures:
⚫ Certain digits + one uncertain digit (an estimate)
Example:
How many significant figures do the following
measurements have?
⚫ 21.5 oC
⚫ 0.02 L
⚫ 0.205 g
⚫ 0.50 M
⚫ 1000 mL4
1. Disregard all initial zeros
2. Disregard all final zeros
unless they follow a decimal
point
3. All remaining digits including
zeros between nonzero
digits are significant
Three s.f.
One s.f.
Three s.f.
Two s.f.
?
▪ 1000 mL at least one significant figure
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1 × 103
1.0 × 103
1.00 × 103
1.000 × 103
One s.f.
Two s.f.
Three s.f.
Four s.f.
1 × 10-3
1.0 × 10-3
1.00 × 10-3
1.000 × 10-3
One s.f.
Two s.f.
Three s.f.
Four s.f.
Significant Figures in Measurements
Use scientific notation
▪ Exact numbers obtained from definitions or by
counting numbers of objects can be considered
to have an infinite number of significant figures
▪ Examples:
⚫ 1 atm
= 76 cmHg
= 760 mmHg
= 760 torr
= 101325 Pa
⚫ 0.2786 g x 8 = 2.229 g6
Significant Figures in Definitions
⚫ 0 oC
= 273.15 K
▪ Measurement: Certain digits + One Uncertain digit
(estimate)
▪ Ex: Graduated cylinder
Certain to 3.1 mL
Read an estimate (0.05)
Reported to 3.15 mL
(three s.f.)
▪ Ex: Buret
Certain to 29.6 mL
Read an estimate (0.02)
Reported to 29.62 mL (four s.f.)7
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Measurement in Graduated Instruments
▪ Take all the digits on display (last digit is an estimate)
⚫ Electric balance reports to 0.24 g (two s.f.)
⚫ Analytical balance reports to 8.6202 g (five s.f.)
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Measurement in Electronic Instruments
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1.75
＋ 9.1
————
10.85
Ans: 10.9 (round to the first decimal place, three s.f.)
◼ Addition and Subtraction:
retain one uncertain digit (estimate)
172.63
－ 1.3
—————
171.33Ans: 171.3(round to the first decimal place, four s.f.)
Significant Figures in Calculation
Significant Figures in Calculation
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222
× 1.1
————
222
222
————
244.2
Ans: 2.4 × 102 (two s.f.)
(three s.f.)
(two s.f.)
(round to the tens place)
◼ Multiplication and Division:
the number of significant figures in the final product or
quotient is determined by the original number that has
the smallest number of significant figures
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◼ Example in Multiplication and Division:
Ex. Molar volume of nitrogen gas
(the original number that has the smallest number of significant
figures is two s.f., the answer is rounded to two s.f. )
731 0.26514 273.15
760 0.0 298
.25605
2
11
21
1
=
=
definitionthree s.f. five s.f.
three s.f.two s.f.
(round to the units place, two s.f.)
Significant Figures in Calculation
definition
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In Logarithms and Antilogarithms:(a) ln a logarithm of a number, keep as many digits to the right of the
decimal point as there are significant figures in the original number.
(b) ln an antilogarithm of a number, keep as many digits as there are
digits to the right of the decimal point in the original number.
log (2.00 × 104)
= log (104) + log (2.00)
= 4 + 0.301
= 4.301 (round to the third decimal place)
[H+] = 2.0 × 10-12 M
= - log (2.0 × 10-12)
= 12 - log (2.0)
= 12 - 0.30
= 11.70
pH = - log [H+]three s.f.
Significant Figures in Calculation
Ex. Example of a pH value:
two s.f.
(round to the second decimal place)
(a)
(b) Convert pH = 8.74 to [H+]:
antilog 8.74 = 1.819 x 10-9 M, following rule (b), retain only two digits
The answer is 1.8 x 10-9 M (round to the first decimal place)
Determination of Chemical Formula
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Mass of empty test tube: 42.4953 g (six s.f.)
Mass of test tube and CuO: 43.5361 g (six s.f.)
Mass of test tube and Cu: 43.3300 g (six s.f.)
Mass of CuO: 43.5361 - 42.4953 = 1.0408 g (five s.f.)
Mass of Cu: 43.3300 - 42.4953 = 0.8347 g (four s.f.)
Mass of Oxygen: 1.0408 - 0.8347 = 0.2061 g (four s.f.)
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0.8347
63.6＝0.0131
0.2061
16＝0.013
Effects of Formula
Weight Used
Determination of Chemical Formula
(four s.f.)
Moles of CuO:
Moles of oxygen:
(four s.f.)
( Mole ratio of Cu and O )
The empirical formula is CuO
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Experimental Measurements
Mass of H2NSO3H:1.0725 g
Molecular weight of H2NSO3H: 97.10 g/mol
R.T.: 28.0 oC
PH2O: 28.3 mmHg
Patm: 76.57 mmHg
Mass of beaker: 154.66 g
Mass of beaker and water collected: 418.13 g
Use equation in lab manual:
STP
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OHatm
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NSTP
Tn
V)P(P
Tn
ΔV)(VP
(K) 273.15(mol) 1
(L)V(atm) 1 22
−=
+=
(thermometer, three s.f.）
(barometer, four s.f. ）
(appendix, three s.f.）
(five s.f.)
1. Use formula weight
in your prelab report
2. Use periodic table in
appendix:
MW H2NSO3H = 3 ×1.008 + 1 × 14.01 +
1 × 32.07 + 3 ×16.00 = 97.10
Molar Volume of Nitrogen Gas
(five s.f.)
(five s.f.)
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Periodic Table (IUPAC dated 1 Dec 2018)
• An interval in square brackets provides the lower and upper bounds of the
standard atomic weight for that element.
• For users needing an atomic-weight value for an unspecified sample with
disregard to the uncertainty, the conventional values are provided.
n1 = 1.0725 / 97.10 = 0.011045314109 (mol) (four s.f.)
T1 = 28.0 + 273.15 (infinite s.f.) = 301.15 (K) (four s.f.)
Ｐatm - ＰH2O ＝765.7- 28.3 = 737.4 (mmHg) (four s.f.)
1 atm = 760 mmHg (infinite s.f.)
∆V：418.13-154.66
= 263.47 g ÷ 1 g/mL
= 263.47 mL = 0.26347 L (five s.f.)
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VSTP = 20.99294
= 20.99 (four s.f.)
Molar Volume of Nitrogen Gas
1. Do the rounding until the calculation is completed
2. At least one extra digit beyond the significant figures should be carried through all of
the computations in order to avoid a rounding error
(four)
infinite
0.011045(four)
(four)
301.15
0.26347(five) 273.15
(infinite)
(765.7 - 28.3)
1.008－0.0372＝0.971
(atm, three s.f.)
）（
= 21.0 (three s.f.)
= 1.008 atm－0.0372 atm
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Reports
Principle: explain concisely, indicate important
theory, laws, and chemical reaction
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Chemicals: Focus on Properties and Toxicity
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• Tabulate the properties (indicate your sources)
• Only few chemicals are not toxic, such as starch, mostly are irritating and
harmful to human body.
• Molecular weights referred should have more than four significant figures.
Chemicals: write down names, formulas, formula weights,
physical properties, chemical properties, toxicities
Chemicals
Formula
wt.FormulaDensitybp / mp
Appearance ToxicitySolubility
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Procedure: Outline the Sentences
Use Flow Chart and Leave Space to Record the Observation
▪ NaNO2: colorless to light
yellow, hygroscopic
▪ NaNO2：1.05 g
▪ Exothermic
▪ React fast
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Procedure Observation
N1, N2, N4, N5, N7
E1, E2, E4, E5, E7, E9
C1, C2, C4, C5, C6, C7, C8-1 , C9
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▪ Hand in the report at the end of the class.
▪ Hand in lab report on time, including prelab report,
records, and final report
▪ Late submission: -5 points within a week
▪ Miss contents: -5 points per category
I. Prelab report
✓ Objective
✓ Principle
✓ Chemicals
✓ Procedure
II. Exp. Records
✓ Observation
✓ Operation
✓ Reaction condition
✓ Data and results
III. Final report
✓ Data analysis
Brief Version Report
N3, N8, N10, N13
E13, E20, E22, E23
C8-2~4, C20, C23, C24
I. Prelab report
✓ Objective
✓ Principle
✓ Chemicals
✓ Procedure
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II. Exp. Records
✓ Observation
✓ Operation
✓ Reaction condition
✓ Data and results
III. Final report
✓ Data analysis
✓ Error analysis
✓ Questions and
discussion
✓ Feedback and
suggestion
▪ Hand in the report in the next week of the class.
▪ Hand in lab report on time, including prelab report,
records, and final report
▪ Late submission: -5 points/1 day
▪ Miss contents: -5 points/1 category
Full Version Report
Error Analysis: explain your results reasonably
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Reasons lead to negative biases (might be true reasons):
your result shows negative error
Reasons lead to positive biases (not true reasons):
Category Guidelines
I. Prelab
report
1. Indicate the main principles and chemical equations in summary.
2. List the chemicals’ physical, chemical properties, and toxicity.
3. Use the flow chart to explain the procedures concisely.
II. Lab
record
4. Record the data with correct significant figures and units.
5. Record the observations, operation, and reaction condition in
details.
III. Results
&
discussion
6. Process the data correctly, including the equations and calculation.
7. Indicate the final results with correct significant figures and units.
8. Analyze the results and make the appropriate discussion.
9. Plot the results with appropriate XY axis and indicate each curves.
10. Provide the concrete outcome and constructive suggestion.
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Scoring Rubrics for Lab Report
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