1. Chapter 2 Measuring and Calculating
HONORS CHEMISTRY
Chapter 2
Measuring and Calculating

2. General Problem Solving
Understand Situation
Appreciate importance or unimportance of info.
Organize info.

3. Problem Solving Techniques:
1. Identify known facts.
2. Define answer required.
3. Develop possible solns.
4. Analyze poss. solns. & determine correct one.
5. Develop steps to answer.
ALGORITHM - pattern for solving a particular type of prob.

4. Problem Solving Techniques:
6. Solve problem.
7. Evaluate results
- number and units

5. Know 3 things to make a measurement
1. What you’re measuring
2. Standard w/ which to compare measurement
3. method of making comparison

6. Qualitative Measurement - Described in words
No numbers
Quantitative Measurement - described by a number of std. units

7. SI is modern version of metric system
7 Basic units
Learn them!
Prefixes are used to obtain different units

8. Mass - a meas. of the quantity of matter
Does not vary from place to place
Kilogram - SI std. unit for mass
Weight - meas. of force of gravity betw. 2 objects
Can vary from place to place
Newton (N) - Meas. std. for weight or force

9. Length - Distance covered by line segment connecting 2 pts.
Meter - SI std. unit of length
defined in terms of wavelength of light
Time - interval betw. 2 occurrences
Second - SI std. unit of time
defined in terms of electron transition

10. Temperature meas. of average kinetic energy of an object’s particles
a meas. of heat intensity
Heat flows from high temp. to low temp. until equal.
Kelvin (K) - SI std. unit of temp.

11. Celsius Scale
Based on boiling pt. (100oC) and freezing pt. (0oC) of pure water
Diff. is divided into 100 = intervals - Degrees
1 Celsius degree = 1 Kelvin

12. ACCURACY
nearness to accepted value
refers to quality of instrument

13. UNCERTAINTY
estimate of accuracy
+ or x smallest unit

14. PRECISION refers to how close a set of measurements are to one another
also refers to:
unit used in making estimation
number of decimal places
reproducibility
Be as precise as instrument allow
estimate one more place than marked

15. PARALLAX apparent shift in reading when viewed from side
Always take reading straight-on & at eye level

16. Percent Error =
Observed - Accepted X 100%
Accepted

17. Scientific Notation For very large or very small numbers
M X 10n < M < 10
M has 1 nonzero digit in front of decimal pt.
n can be (+) or (-)

18. Significant Digits Indicates exactness of meas. Depends on instrument
Includes all certain digits + 1 estimated digit

19. Calculations w/ Sig. Digits
Add. & Sub. - Answer contains only as many decimal places as the meas. w/ the least # of decimal places
Mult. & Div. - Answer contains only as many sig. digits as the meas. w/ the least # of sig. digits.

20. Derived Units Obtained by combining fundamental SI units
1 dm3 = 1 liter
Liter (L) - unit of volume
1 L = mL = cm3 = 1 dm3
SI unit of volume is the cubic meter
- too large - use dm3 (L)

21. Density mass per unit volume D = m/v
derived unit usually expressed in g/cm3
A change in temp. can change vol. & change density
Values usually 25 oC