SCIENTIFIC MEASUREMENT. Measurements in the Lab:. 23°C. 23°C. The number of SFs in a measured value is equal to the number of known digits plus one uncertain digit. 22°C. 22°C. 21°C. 21°C. you record 21.6°C. you record 21.68°C. Measurements in the Lab :. Example B. Example A.
The number of SFs in a measured value is equal to the number of known digits plus one uncertain digit.
you record 21.6°C
you record 21.68°C
1. If the glassware is marked every 10 mLs, the volume you record should be in mLs. (Example A)
2. If the glassware is marked every 1 mL, the volume you record should be in tenths of mLs.
3. If the glassware is marked every 0.1 mL, the volume you record should be in hundredths of mLs. (Example B)
the volume you write in your lab report should be 13 mL
Buret marked in 0.1 mL: you record volume as 0.67 mL
precision is +/-1g.
Standard lab balance are trustworthy to
the nearest milligram (0.001g)
measurement: 25.000g, so
implied precision is +/-0.001g
The analytical balance is very precise. Measurements are trustworthy to the nearest 0.1mg. Measurement:25.0000
implied precision: +/-0001g
Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 46
Significant figures are all the digits in a measurement that are known with certainty plus a last digit that must be estimated
Mistakes are caused by PEOPLE
Misreading, dropping, or other human mistakes are NOT error
+ 25.2 g
- 33.04 g
1. First line up the decimal places
2. Then do the adding
3. Count the sig figs in the decimal portion of each addend.
4. Round your answer to the place value of the addend with the least number of decimal places
25.2 mx6.1 m= 153.72m (on my calculator)
= 1.5 x102 m (correct answer)
------------ = 7.3122535 g
= 7.31g (correct answer)
(6.626 x 10-34)(3 x 108)
------------------------------- = 3.06759 x 10-2 (on my calculator)
6.48 x 10-24
= 0.03 (correct answer)
NO NAKED NUMBERS!!!!!!!!!!
Based on Powers of 10
Technique Used to
1. Express Very Large or Very Small Numbers
2. Reduce likely-hood of errors
3. Compare Numbers Written in Scientific Notation
Numbers that are very small
The electrical charge on one electron:
0.0000000000000000001602 = 1.602 X 10-19 C
The mass of the moon:
73,600,000,000,000,000,000,000 kg = 7.36 X 1022kg
-- regular shapes – formulas (derived value)
-- irregular shapes – displacement of another liquid, usually water
1 inch = 2.54 cm
Zumdahl, Zumdahl, DeCoste, World of Chemistry2002, page 119
Whether you call it Dimensional Analysis, the Unit Method, or the Factor-Label Method, this is one of the most useful techniques you will learn.
Use it and you will never ask,
“Do I multiply or divide?” when you are converting from one set of units to another.
Measurements include two parts:
a number and the units.
Reporting the distance as 20.0 gives no information at all until the units are included.
Is that 20.0 kilometers, meters, miles, feet, or light-years?
*units of known in denominator (bottom) first
*** units of unknowns in numerator (top
Since these are equal,
they divide to make one
$100 bill X 100 $1 bills X 4 quarters X 5 nickles= 2000 nickles
1 $100 bill 1 $1 bill 1 quarter
2.5 hr X 60min/1 hr = 150 min
By using dimensional analysis / factor-label method, the UNITS ensure that you have the conversion right side up, and the UNITS are calculated as well as the numbers!
2.5 hr 60min = 150min
7.25$ 4 quarters = 29 quarters
1.4day 1day 60min 60sec =
24hr 1hr 1 min
I know I have 15 attendees at the party
What do I need to know?
How much will the party cost me?
party 1 people 12 slices 1 pizza
D = m/v (g/cm3)
Mass usually expressed in grams
Volume usually expressed in cm3 or liters, etc.
EX: cubes, cylinders, spheres, cones, etc.
Your answer should be 2 sig figs so
7.0 X 101 cm3
1 in 1 in 1 in
727.6880608 cm3 X 19.3g X 1 pound = 30.93475677 pounds
1 cm3 454 g
According to significant figures, 30 pounds