1. Chemistry – Sept 7, 2018 P3 Challenge –
State the three meter stick equivalences.
Get out #3 and Factor Label Conversions Homework pg 1 for check

2. Objectives, Agenda and Assignment
To use ratio and square applications
To use the density formula
Agenda
Homework Review
Squared unit conversions
Ratio unit conversions
About Density
What’s Due?
Ratio and Square Factor Label
Prelab questions on the Penny Lab
What’s Next?
Begin Studying for the Unit 1 Test on 9/20

3. Unit Conversions (Factor-Label method)
“Times sign, draw the line, copy the unit.”
Variations on the theme
Multistep conversions
Squared unit conversions
Ratio unit conversions

4. Multistep conversions
“Times sign, draw the line, copy the unit.”
If you do not know of the equivalence between the measured unit, and the target unit, consider a third unit that has an equivalence with both.
Ex: convert 4.75 km to cm (remember sigfgs) km m cm
1000 m
100 cm
4.75 km
= cm 1 km 1 m
= 4.75 x 105 cm

5. Squared unit conversions
If a unit is raised to a power, often 2 or 3, to perform a conversion, you must raise the entire conversion factor to that power.
Convert 22 cm2 to m2 2 1 m
22 cm2
= m2 = 2.2 x 10-3 m2
100 cm

6. Ratio unit conversions
Many derived units involve ratios of units. km/hr, m/s2…
If a unit on the bottom needs to be converted, “copy the unit” to the top.
Ex: Convert 25 m/s to km/h
meter km s
min hr 25 m 1 km 60 s 60
min
= km/hr 1 s
1000 m 1
min 1 hr

7. Density
Density is a characteristic physical property of a substance and is sometimes used to identify a substance.
Density is the mass of an item divided by its volume.
This table lists the density of many common substances.
Notice that solids have the highest density, and liquids usually have lower density. Gases have the lowest densities by far, usually reported in g/L.

8. Understanding density
If density is color, a low density is a pale color, and a high density is a very intense color.
If two objects have the same mass, the smaller one is more dense.
If two objects are the same size, the heavier one is more dense.
1 kg
1 kg
1 kg
4 kg

9. Using the Density Formula
List the known quantities with their units. Let their units help you decide which quantity a value represents. There must be two known quantities.
Substitute these values into the formula.
Calculate the third variable.
Ex: A 1.68 kg object has a volume of 0.75 L. What is the density of this object in g/mL?

10. Exit Slip - Homework
What is density? (formula and what the variables mean)
What’s Due? (Pending assignments to complete.)
Ratio and square on Factor Label Method Worksheet
Prelab questions for the Density of Pennies Lab, Read the lab handout.
What’s Next? (How to prepare for the next day)
Begin Studying for the Unit 1 Test on 9/20.