1. Chemistry – Sept 8, 2017 P3 Challenge – Convert 25 cm to Gm
Get out Factor Label Conversions Homework for check.
Pick up the four handouts when handing in your P3. (Unit 1 Test Study Guide and Review, Next class Lab handout, Graph you’ll need, and instructions for writing a lab report)

2. Objectives, Agenda and Assignment
To use the density formula
Agenda
Homework Review
About Density
Ratio and Square Conversions (if needed)
Scientific Notation (if needed)
What’s Due?
Prelab questions on the Penny Lab
What’s Next?
Begin Studying for the Unit 1 Test on 9/18

3. 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.

4. 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

5. 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 g object has a volume of 0.75 mL. What is the density of this object in g/mL?

6. 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

7. 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

8. Scientific Notation
A clear way to report numbers that are either very large or very small, or numbers with an ambiguous number of significant figures
Two parts: Mantissa x 10exponent
Mantissa, or decimal part, is a number with one non-zero digit to the left of the decimal point that contains all significant digits, and only significant digits
Exponent indicates the decimal place location for the digits.
Exponent = number of places the decimal point must move to be placed to the right of the first significant figure
Large numbers have positive exponents and small numbers have negative exponents.
2000 cm  2.00 x 103 cm makes the significance clear.
Use Sci Not if you need clarity or you need to use more than 3 zeros.

9. ACT Fridays
As a school we are committed to helping you get the highest score possible for you on the ACT.
The science department will be contributing to this initiative by donating a portion of each Friday Science class to work on ACT related activities.
Last Friday we practiced with 2 passages from an actual ACT class.
This Friday we possibly have time to discuss those passages and some test taking strategies.

10. Exit Slip - Homework
What is density? (formula and what the variables mean)
What’s Due? (Pending assignments to complete.)
Prelab questions for the Density of Pennies Lab, and back of Factor label WS
What’s Next? (How to prepare for the next day)
Begin Studying for the Unit 1 Test on 9/19