Announcements

1
Announcements

• CSB due Friday, 400 PM
• Credit mode
• Sections can be repeated only the highest grade
  remains
• IM office hours tonight, 900-1000 PM(unless
  theres a screaming baby)
• Problem Session Monday, 125 PM
• Dr. Reisner will put these on the website by the
  next class.

2
CONVERSIONS
3
Problem Solving Method

• What do you want?
• What do you know?
• How can you use what you know to get what you
  want?
• Does your answer make sense?
• APPLY TO ALL UNIT CONVERSION PROBLEMS!

4
Practice with the Problem Solving Method

• How many revolutions does the hour hand on a
  clock make in a year?
• What do you want? (be specific what units are
  you trying to calculate)
• What do you know?
• Setup Solve.

Group Activity
5
Measurements and Numbers

• All numbers have units!numbers are meaningless
  without units
• length meters m
• volume liters L
• temperature degrees C

6
Measurements and Numbers

• Some ways of expressing numbers are better than
  others!
• 0.0000000012 m or 1.210-10 m
• CSB appendix

7
Measurements and Numbers

• Significant figures matter!
• Theophylline chronic asthma
• therapeutic range 10. 20. mg/mL
• toxic effects 25 mg/mL (fatal seizures)
• acceptable dose?
• Chem131L activity

8
Metric Conversion Factors

• prefix amount
• giga G 109 109 m 1 GM
• mega M 106
• kilo k 103
• centi c 10-2
• milli m 10-3
• micro m 10-6
• nano n 10-9
• pico p 10-12

9
Metrics and the Problem Solving Method

• Suggest a strategy to determine which of the
  following numbers is the smallest using the
  problem solving method. Show your work.
• 2.577 ? 10-1 kg
• 2.577 g
• 2.577 ? 104 mg

Group Activity
10
Density as a Conversion Factor

• d m/Vdensity mass/volume
• OR
• mass-volume relationship
• dHg 13.6 g/mL
• 13.6 g Hg 1 mL Hg

11
Notecard Questions

• Work should be your own.
• Discussion okay.
• Time limited.
• Pass them to the center then down to the front.

Notecard Question
12
Density and the Problem Solving Method

• You accidentally break a thermometer and find
  that the mercury that comes out has a mass of
  0.34 g. What volume of mercury was contained in
  the thermometer (The density of mercury is 13.6
  g/mL.)
• What do you want? (units)
• What do you know? (facts and relationships)
• Set up and solve.

Notecard Question
13
Problem Solving Practice

• The mass of the earth is 5.35 ? 1027 grams. The
  thin outer layer of the Earth, called the crust,
  contains only 0.50 percent of Earths total mass
  and yet is the source of almost all the elements
  (the atmosphere provides elements such as oxygen,
  nitrogen, and a few other gases). Silicon is the
  second most abundant element in Earths crust
  (27.2 percent by mass). Calculate the mass of
  silicon in kilograms in Earths crust.

Use the problem solving method!
Group Activity
14
Problem Solving Practice

• The solubility of sodium fluoride is 4.22 g in
  100 mL water at 18 C. A solution is made up of
  435 mg of sodium fluoride in 25.0 g of water. Is
  the solution saturated? See how you can apply
  the problem solving method that you learned in
  class.

Start by determining a strategy using the problem
solving method.
Group Activity