Every measurement we make includes some uncertainty. We can never measure something exactly or know...
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Transcript of Every measurement we make includes some uncertainty. We can never measure something exactly or know...
![Page 1: Every measurement we make includes some uncertainty. We can never measure something exactly or know a quantity with absolute certainty. The numbers.](https://reader035.fdocuments.us/reader035/viewer/2022062322/56649ead5503460f94bb3bf7/html5/thumbnails/1.jpg)
![Page 2: Every measurement we make includes some uncertainty. We can never measure something exactly or know a quantity with absolute certainty. The numbers.](https://reader035.fdocuments.us/reader035/viewer/2022062322/56649ead5503460f94bb3bf7/html5/thumbnails/2.jpg)
Every measurement we make includes some uncertainty. We can never measure something
exactly or know a quantity with absolute certainty.
The numbers (quantity) we use must tell us two things: 1. How large or small 2. How well were you able to measure it
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The digits we record in a measurement (certain and uncertain) are called, significant figures (sig. figs).
The greater the # of sig. figs in a measurement, the greater the certainty.
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In general, all digits are significant, except zeros that are not measured but are used to position the decimal point (place holders).
![Page 5: Every measurement we make includes some uncertainty. We can never measure something exactly or know a quantity with absolute certainty. The numbers.](https://reader035.fdocuments.us/reader035/viewer/2022062322/56649ead5503460f94bb3bf7/html5/thumbnails/5.jpg)
• Leading zeroes never count as sig. figs There are only 3 sig. figs in the quantity 0.00275
kg.• Internal zeroes always count as sig.
figs The quantity 1.004 g has 4 sig. figs
• Trailing zeroes count as sig. figs only if the decimal point is written. The quantity 12.40 mL has 4 sig. figs, but the
quantity 250 mL has only 2 sig. figs.
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How many sig. figs are in… Answer12.35 g 4 (count all non-zero digits, not
just decimal places)
0.00568 L 3 (leading zeroes never count)
3.007 g 4 (internal zeroes always count)
21.0 °C 3 (trailing zeroes count if decimal is showing)
500 mL 1 (trailing zeroes do NOT count if no decimal is showing –– but don’t leave them out, or it looks like 5 mL!)
0.0250 L 3 (leading zeroes never count, but trailing zero counts if decimal is showing)
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Sig. Figs
Sig. Figs
a. 0.103 cm i. 2, 300 g
b. 2.306 in j. 8.10 L
c. 21 k. 2.40603 x 105 µm
d. 0.032 mL l. 0.000200 kg
e. 1000 mL/L m. 144
f. 100. Lbs n. 1001 tons
g. 85 boxes o. 340. lbs
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Answers to calculation cannot be more accurate than the information you entered in calculation- but calculators don’t know that.
2 rules when reporting the uncertainty in calculations. Addition and Subtraction Division and Multiplication
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When adding or subtracting, round off to the fewest number of decimal places.
22.9898 g 1.00794 g12.011 g47.9982 g84.00694 g, round to 5 sig. figs 84.007
g
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Keep the same number of sig. figs. as the measurement with the least number of sig. figs
Example : 1.2m X 2.00m = 2.4 m
The first measurement 1.2 has 2 sig. figs The second measurement has 3 sig. figs. So your answer may only have 2 sig. figs
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1.234g + 2.2g + 3.45g =2.2m X 333m =47.0 m 2.2 s =4.257 kg x (1019 m2 – 40 m2) (54.5
s x 31.3 s)
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6.9 g7.3 X 102 -You have to change the number to
scientific notation because that is the only way you can have two sig. figs
21 m/s2.44 kg·m2/s2
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You’ve observed the changes that occur when you place a piece of Al foil into a blue solution. Lots of observations (avoid jumping to
conclusions) Bubbles form (gas behaves like H2 gas)
You’ve observed the relationship between P and V Best to quantify observations (measured
volumes while applying pressure) PV = constant (1662 Robert Boyle- Boyle’s
Law)
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Boyle’s Law describes what gases do, but not why. To answer the “why” we need a model.
Imagine air as a collection of particles (tiny-ping pong balls) bouncing around inside syringe.
Tiny particles = molecules
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Every time a molecule hits the syringe wall or plunger, it pushes against surface. The surface pushes back and molecule
bounces off in another direction.
This process is called gas pressure.
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Now, let’s say we decrease the volume of the syringe. What happens to the molecules inside the syringe ? They move! Smaller volume = more collisions =
more gas pressure This moving-particles model of gases is
called the kinetic molecular theory of gases.
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You bet!
Here are some examples: Inflating a bike tire Inflating a balloon
All gases obey Boyle’s Law and KMT of gases seems to explain gas pressure behavior for all gases.
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Absolutely not! Think gas splint test. Example: CO2 extinguishes flame
Different gases= different molecules (particles are always moving and bouncing around, PV relationship is the same)
Now, the question is what happens when different kinds of gases are combined?