1. CH 2: Scientific Measurement
Renee Y. Becker
CHM 1025
Valencia Community College

2. Measurement A number with an attached unit
Measurements
Measurement
A number with an attached unit
Examples: 15 inches cups cm
Every measurement must include units!!

3. Example 1: Measurements
In the following, what are the measurements and what are the units?
a) 12 trees
b) 2.3 mm
c) 100 ¢

4. Instrument A device for recording a measurement
Measurements
Instrument
A device for recording a measurement
Examples: Ruler (length), electronic balance (mass), Graduated cylinder (volume)

5. Uncertainty
An instrument may give a very sensitive reading, but EVERY measurement has UNCERTAINTY
No measurement instrument is perfect and neither is the person using it

6. Example 2: Length Measurements
If we need to measure the length of this candycane, which ruler should we use? Why?

7. Mass Weight Measure of the amount of matter it possesses
Measured by a balance
Not affected by gravity
Typical units: kilogram (kg), gram (g), pound (lb), ounce (oz)
Weight
Force exerted by gravity on an object

8. Balances

9. Would you have the same mass on the moon as on Earth? Why?
Example 3: Mass
Would you have the same mass on the moon as on Earth? Why?
Would you have the same weight on the moon as on Earth? Why?

10. Volume The amount of space occupied by a solid, gas, or liquid
Graduated cylinder, pipet, buret, volumetric flask, syringe
Typical units: milliliter (mL), Liter (L), centimeter cubed (cm3), quart (qt), gallon (gal),

12. Buret

13. Accuracy, Precision, and Significant Figures in Measurement
Accuracy is how close to the true value a given measurement is.
Precision is how well a number of independent measurements agree with one another.

14. Accuracy, Precision, and Significant Figures in Measurement
Significant Figures are the total number of digits in the measurement.
The results of calculations are only as reliable as the least precise measurement!!
Rules exist to govern the use of significant figures after the measurements have been made.

15. Accuracy, Precision, and Significant Figures in Measurement
Rules for Significant Figures:
Zeros in the middle of a number are significant
Zeros at the beginning of a number are not significant
Zeros at the end of a number and following a period are significant
Zeros at the end of a number and before a period may or may not be significant.

16. Example 4: Significant Figures
How many Sig. Figs ? a) b)
c) 36,450 d) e)

17. Accuracy, Precision, and Significant Figures in Measurement
Rules for Calculating Numbers:
During multiplication or division, the answer can’t have more sig figs than any of the original numbers.

18. Example 5: Significant Figures
12 / =
x 0.29 =
/ =

19. Accuracy, Precision, and Significant Figures in Measurement
-During addition or subtraction, the answer can’t have more digits to the right of the decimal point than any of the original numbers.

20. Example 6: Significant Figures= = = =

21. Accuracy, Precision, and Significant Figures in Measurement
Rules for Rounding Numbers:
If the first digit removed is less than 5 - round down
If the first digit removed is greater than 5 - round up
If the first digit removed is 5 and following numbers are nonzero - round up
If the first digit removed is 5 and following numbers are zero - round down
Only final answers are rounded off, do not round intermediate calculations

22. Round off each of the following measurements
Example 7: Rounding
Round off each of the following measurements
L to four significant figures
(b) K to three significant figures
(c) kg to four significant figures

23. Example 8: Accuracy & Precision
Which of the following is precise but not accurate?

24. Changing numbers into scientific notation Large # to small #
Moving decimal place to left, positive exponent
123,987 = x 105
Small # to large #
Moving decimal place to right, negative exponent
= 2.39 x 10-4
Correct scientific notation:
#.#### x 10n

25. How to put into calculator??
Scientific Notation
How to put into calculator??

26. Example 9: Scientific Notation
Put into or take out of scientific notation
87542
x 10-3
0.784
2.78 x 106
92000

27. When we count something, it is an exact number.
Significant Figures
When we count something, it is an exact number.
It has an infinte number of significant figures