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# Chem2

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• 1. Ratios and dimensional analysis
• 2. Do now
1. A classroom is 7.0 m wide, 10 m long, and holds 25 people. What is the population density of the classroom?
2. Scientifically notate: 84.029 ; 0.000541 ; and 623.000
• 3. Ratios
speed = distance/time
density = mass/volume.
d = m/v
(mnemonic: DMV)
• 4. Ratios
e.g. If a metal block has a mass of 75 grams and a volume of 22 cubic centimeters, what is its density?
75 g/22 cm3= 3.4 g/cm3
• 5. Density of some common substances
• 6. Ratios
• 7. Ratios
The density of air is .0013 g/cm3.
Find the mass of 200 cm3 of air.
d=m/v
m/v = d
m=dv
m= .0013 g/cm3 x 200 cm3
• 8. Ratios
Tonya goes swimming. When she takes a deep breath and holds it, she is able to float on water. When she exhales, she sinks. Why?
• 9. Q: How do you not sink in quicksand?
(video)
• 10. Dimensional analysis
One of the most useful things! Ever!
Q. How many seconds are there in 1 hour?
1 hr x 60 min/1hr x 60 sec/1min = ?
• 11. Dimensional analysis
1 in = 3.54 cm
1 ft = 12 in
Q. How many feet are in 86 cm?
• 12. Practice
1 m = 100 cm; 1 cm = 10 mm
1 in = 2.54 cm
1. Convert 75 mm to inches.
75 mm x 1 cm/10 mm x 1 in/2.54 cm =
• 13. Quiz