1. Ch. 3, Scientific Measurement

2. Measurement
Measurement: A quantity that has a number and a unit. Like 52 meters.

3. Scientific Notation
Writing long numbers as smaller ones to a power of ten.
1,400, = x = E6
= x 10 — = 5.6E-4
15,093,000 = x = E7
----- Meeting Notes (9/4/14 11:04) -----
Rules - decimal after first number

4. Accuracy vs. Precision
*Accuracy: How close a measurement comes to the correct value.
*Precision: How close a series of measurements are to one another.

5. Determining Error of a measurement
Error = Experimental Value - Accepted Value
Can be positive or negative
Percent Error = error / accepted value * 100% or
Always positive
Example, you measured 99 cm, but it is 100 cm.
----- Meeting Notes (9/4/14 11:04) -----
define experimental and accepted.

6. Significant Figures: The digits in a measurement that are known plus one that is not known.
Filled 43.1 mL

7. Rules for Sig Figs Non-Zero Numbers are always significant
Ex) .236 m has 3 sig figs.
Zeros between non-zero numbers are significant.
Ex) 7003 m and m each have 4 sig figs.
Leftmost zeros are not significant
Ex) m, 0.42 m, and .073 m each have 2 sig figs.
Rightmost zeros are significant if they come before or after a period.
Ex) m, m, and m each have 4 sig figs.

8. Rules for Sig Figs
Rightmost zeros with no decimal points are no significant.
Ex) 300 m has 1 sig fig.
Exactly defined quantities have an unlimited number of sig figs.
Seen most when converting between measurements.
60 min = 1 hour, cm = 1 m each have an unlimited number of sig figs.

9. Is a Zero a Significant Number or Not?
504 L
.06 mL
50.0 m
7,000 km

10. Sig Figs in Calculations:
Calculations cannot be more precise than the least precise measurement.
Addition or subtraction - Round the final answer to the same number of decimal places as the measurement with the least number of decimal places.
the last “shared column”.
13.4 m m = 18.7 m

11. Sig Figs in Calculations:
Multiplication or Division - The final answer should have the same number of sig figs as the measurement that has the least number of sig figs.
m x 8.4 m = 21 m

12. In this class, delay rounding until the very end.
(3.449L L) * 8.779L / 5.2L = 17L

13. International System of Units
How much of something you have is given by Units. Like centimeters, kilometers, etc.
SI is the standard measurement system for science.

14. * The five SI units used most by chemists are:
Distance = meter (m)
Mass = kilogram (kg)
Temperature = kelvin (K)
Time = second (s)
Volume = liter (L)
Amount = mole (mol).

15. Prefixes can be used in front of units for powers of 10.

16. Mass = how much “stuff” is in something
Mass = how much “stuff” is in something. How much matter is in something.
Weight = the pull on something by gravity.
If I go to the moon, which changes and which stays constant?
-Weight changes, mass stays the same.

17. Temperature:
Celsius and Kelvin are units of temperature that are the same, just shifted.
K = C + 273
Water freezes at 0 C and at 273 K.
Absolute Zero = 0 K; a K value will never be negative.

18. *Energy * Energy - The ability to do work or produce heat.
Joule (J) is the SI unit of energy.
Calorie (cal) is another unit of energy.
1 J = .239 cal

19. Conversions
Convert 7 mm to m. Convert 12.4 Mm to cm.

20. Convert 7 km/ms to m/s
An experiment asks students to measure 1.50 g of Cu wire. All we have is a 40.0 g spool of Cu. How many students can do the experiment?

21. *Density *Density = mass / volume
What is the density of 2 g of salt in a volume of 4 L?
What is the density in g/L of 5 kg of salt in a volume of 6 mL?

22. If silver has a density of 10
If silver has a density of 10.5 g/L, what is the volume of a silver coin that has a mass of 14 g?

23. Density decreases as temperature increases.
D=m/v
As T increases, V increases.
Therefore, density decreases.

24. Example Problems!!!

25. 1. How many sig figs in: * E3
2. Perform these calculations and come up with answers that have the correct number of sig figs: E3 / E3 * 3
3. Convert 3.4 ng into kg.
4. Convert 7E3 cm into Mm.
5. What is the mass if a substance with a density of g/L has a volume of 3 L?

26. 6. How many sig figs in:
7. Convert 3 kg into g Convert 34 cm into m Convert 4 m into cm.
8. You have a 4 kg box. You measure it to be 5.8 kg. What is the error? The % error?
9. What is the difference between mass and weight? Accuracy and precision?

27. 11. Put 5,009,000,000 into Scientific Notation
13. Put 8.7 * 10-4 into a regular number.

28. 14. Which is the largest amount?
A. 2*102 g B. 30 kg C. 45 mg D g
15. Convert 40 Kelvin into Celsius
16. Convert 99 Celsius into Kelvin.