1. Introduction to Chemistry Part 2
Significant Figures (aka- “sig figs”)
Density Calculations

2. Two step unit conversions
If you do not have a conversion factor between the given unit and the one you are looking for, you must do two conversions.
Example- How many milliliters are in kiloliters?

3. Practice
1) 254 mm =____________km
2) kg = ___________mg
3) 46 cL = _____________ kL
4) 675 km = ____________ cm
5) kL = ___________mL
6) 97.8 mg = _____________kg
7) 1.88 ms = ______________ cs
8) 6.48 cm = _____________mm
9) kL = ____________ mL
10) 25 mm = ______________cm
** All of the given units and all of the units I asked for have a prefix… that means it is a two step problem!
Convert to the base unit first!!!!

4. Significant Figures Sig Fig Rules All non-zeros are significant.
All zeros in-between significant numbers are significant.
Zeros to the right of a decimal after a whole number (greater than or equal to one) are significant.
Zeros to the right of a decimal after a significant number are significant
Examples (underlined are significant)
123= 3 sig figs = 2 sig figs
10003= 5 sig figs = 4 sig figs = 4 sig figs
= 6 sig figs = 1 sig fig (not a whole number)
= 4 sig figs = 5 sig figs

5. Sig Fig Practice
1234
9.0x10-3
0.023
9.010x10-2
8120
890
7.991x10-10
91010 72
9010.0
780.
1000
3.4x104
0.0001

6. Accuracy is how close a measured value is to the actual (true) value.
Accuracy vs Precision
Accuracy
Accuracy is how close a measured value is to the actual (true) value.
Precision
Precision is how close the measured values are to each other.

7. Rounding to the correct number of sig figs
Express the following using 3 sig figs
600
48000
326451
3995

8. Multiplying / Dividing / Trigonometric Functions
a) First perform all the operations, even if changing from one formula to another.
b) Round off the result so that it has the same number of sig figs as the least of all those used         in your calculation.
Example: (2.5 m) x (2.01 m) x (2.755 m) = m
Answer = 14 m3     (2 sig figs)

9. Addition / Subtraction
When measurements are added or subtracted, the answer can contain no more decimal places than the least accurate measurement.
Example: 153. ml + 1.8 ml  ml =  ml
Answer = 164 ml

10. Density
Mass per unit volume How far apart the molecules are m V
D =

11. Density Example Problem
What is the volume of 325 g of metal with a density of 9.0 g/cm3?