1. 1 Brainteaser August 6 th, 2012  If the mass of a lead cube is 176.91 g and it measures 2.51cm x 2.49 cm x 2.49 cm, what is the density of lead?  Remember: Density is Mass/Volume!!

2. 2 Agenda  Dimensional Analysis (DA) notes  DA in-class worksheet  HW:  Find 3 interesting facts about to chemistry  Sig Figs calculations practice

3. Dimensional Analysis August 6 th, 2012

4. 4 Dimensional Analysis Vocabulary  A tool. An organized technique of converting between units.  Equivalence statement  Conversion factors (ratio)

5. 5 Dimensional Analysis Equivalence Statement Examples: Conversion Factors Examples:  Relates the same quantity in two different units  An equation that is always equal.  Ratio between units in the equivalence statement 1 gallon = 3.785 L 2.54 cm = 1 inch

6. 6 DA Example #1 w/Pictures I want you to convert 1 apple to lemons using the following equivalence statements:  1 apple = 1 orange  1 orange = 3 lemons  Draw pictures to show the conversion! =

7. 7 DA Example #2 w/Written Units  How many eggs are in two cases using the following equivalence statements:  1 case = 24 cartons  1 carton = 12 eggs = 2 cases 1 case 24 cartons 1 carton 12 eggs2 x 24 x 12 1 x 1 = 576 eggs

8. 8 Dimensional Analysis  How to use Dimensional Analysis (DA) 1.Identify the unknown. What is the problem asking you to find? 2.Start with the given (often the first # in the problem) 3.Identify and set up the conversion factors for each unit of change 4.Make sure all units cancel EXCEPT the one you are looking for. 5.Check that you have the correct number of significant figures. 6.Ask whether your answer makes sense.

9. 9 Sample Problems  How many kilograms are in 125 g of salt?  Chloroform is a liquid once used as and anesthetic. What is the volume in mL of 5.0 g of chloroform. Density = 1.49 g/mL?  The length of a marathon race is approximately 26.2 miles. What is the distance of the race in kilometers? 5280. feet = 1 mile  Convert the freeway speed limit of 65 miles per hour to kilometers per second. 1 km = 0.62 mi

10. 10 Summary  What is dimensional analysis used for?  Why is it useful?  What must accompany every number (measurement) in chemistry?