1. Dimensional Analysis

2. SI Units- System International d’Unites
Quantity
Symbol
Base Unit
Abbrev.
Length l
meter m
Mass m
kilogram kg
Time t
second s
Temp T
kelvin K
Amount n
mole
mol

3. Volume Units
Volume: a liquids volume is found in a graduated cylinder but a solid is found by calculating LxWxH
therefore:
1ml =1cm3
1 cm x 1 cm x 1 cm = 1 cubic centimeter

4. Must Memorize!!! 1000 base unit = 1 kilo- (Ex: 1 km = 1000 m)
1 base unit = 1000 milli- (Ex: 1 m = 1000 mm)
1 base unit = 100 centi- (Ex: 1 m = 100 cm)

5. Number vs. Quantity UNITS MATTER!! Quantity - number + unit
In Science a number without a unit is WORTHLESS!
UNITS MATTER!!

6. Accuracy vs. Precision ACCURATE = CORRECT PRECISE = CONSISTENT
Accuracy - how close a measurement is to the accepted value
Precision - how close a series of measurements are to each other
ACCURATE = CORRECT
PRECISE = CONSISTENT

7. Dimensional Analysis-”Bridge”
The “Factor-Label” Method
Units, or “labels” are canceled, or “factored” out

8. Dimensional Analysis Steps:
1. Identify given & unknown (starting & ending units)
2. Line up conversion factors so units cancel.
3. Multiply all top numbers then multiply all bottom numbers and then divide.
4. Check units & answer.

9. Conversion Factors
Conversion factors are equivalences of measurements just in different units
Example: 1 mile = 5,280 ft
Conversion factors can be put into fraction form which is equal to one no matter which is on top and which is on bottom

10. Lets try one….
2.8 yrs. to hours
____ years to seconds

11. Practice
500 m  miles

12. Numbers in Science
Exact numbers are numbers known to be absolutely correct and are obtained by counting or by definition. (Used in math class)
Measured numbers involve some estimation. Significant digits are believed to be correct by the person making and recording the measurement.

13. Significant Figures 2.35 cm Indicate precision of a measurement.
Recording Sig Figs
Sig figs in a measurement include the known digits plus a final estimated digit
You can only be as precise as the instrument you are using!!!!
2.35 cm

14. Rules for Significant Figures
Non-zero digits and zeros between non-zero digits are always significant
Leading zeros are not significant
Zeros to the right of all non-zero digits are only significant if a decimal point is shown
For values written in scientific notation the digits in the coefficient are significant

15. Counting Sig Fig Examples
4 sig figs
3 sig figs
3. 5,280
3. 5,280
3 sig figs
2 sig figs

16. Trick for Significant Figures

17. Practice Significant FiguresL
18.6 mL
2,000 km
18, 345, 600 mm

18. Sample Problems
How many Significant figures are in the following measurements?
3.57 ml
2880 ml
280. ml
24.05 g
3.20 x 104 kg

19. Scientific Notation 65,000 kg  6.5 × 104 kg
Converting into Sci. Notation:
Move decimal until there’s 1 digit to its left. Places moved = exponent.
Large # (>1)  positive exponent Small # (<1)  negative exponent
Only include sig figs.

20. Practice Problems 2.4  106 g 7. 2,400,000 g 8. 0.00256 kg
9. 7  10-5 km
 104 mm
2.56  10-3 kg km
62,000 mm

21. Scientific Notation Type on your calculator: = 671.6049383 = 670 g/mol
Calculating with Sci. Notation
(5.44 × 107 g) ÷ (8.1 × 104 mol) =
Type on your calculator:
EXP EE
EXP EE
ENTER
EXE
5.44 7
8.1 ÷ 4 =
= 670 g/mol
= 6.7 × 102 g/mol

22. B. Percent Error your value accepted value
Indicates accuracy of a measurement
your value
accepted value

23. Percent Error % error = 2.9 %
A student determines the density of a substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.
% error = 2.9 %