Calibration, Percent Error, Density

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Calibration, Percent Error, Density Temperature
Mr. Shields Regents Chemistry U00 L04
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Common Volume Measurement Devices
Capacity
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What is Calibration?

• The calibration of a measuring device is the
  distance between the two closest lines.

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source
Capacity ? Calibration ?
100 ml
1 ml
source
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Calibration
If the calibration on a scale is 0.1g we can
determine the mass of something to at least that
level of accuracy. For example 219.4g
But we can do better than that! We can also
estimate one digit greater than that. For
example we could measure 219.43g. The 3 is
the estimated value. Note that Zero can be
an estimated value as well as the numbers 1-9.
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source
Calibration ?
1 ml
source
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Capacity ? Calibration ?
10 ml
0.2 ml
Reading?
8.80 ml. The zero is our estimated Value. It is
significant and can not Ignored.
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Whats the calibration?
Meter Stick
source
On this meter stick, the closest lines are 1
millimeter or 0.001 meter apart.
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Whats the calibration?
0.1 gram
What can we estimate to?
0.01 gram
Triple beam balance
Whats the reading?
373.35 g
source
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This is part of a buret. Note The numbers
increase downward, so you read top to
bottom. Whats The calibration? Whats the
reading?
0.1 ml
source
21.35 ml
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PERCENT ERROR
Now Lets look at at a set of experimental B.P.
Data collected by two students
Student 1 Student 2 76.5 deg C 78.0 deg C 76.1
78.4 76.6 77.9 76.9 78.2 76.5 AVG 78.1
AVG
The Accepted B.P. for this unk. is 77.2 deg
C. Which set of data is more precise which
set Of data is more accurate?
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Percent Error
The data for student 1 looks better but how
much better was that data than student 2s data?
To make this comparison we need to look at the
error for each students set of data Formula for
ERROR Experimental Value Accepted Value
x 100 Accepted Value
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Problem If student 1s Exp. Value was 76.5 and
the Accepted value Is 77.2 what is her
experimental error?
Student 1 76.5 - 77.2 x 100. -
0.907 Error
77.2 Student 2 78.1 - 77.2 x 100.
1.17 Error
77.2 NOTE ONLY THE SIZE OF THE ERROR
IS IMPORTANT. IGNOR PLUS () AND MINUS (-) SIGNS.
So which student has the more accurate
data? Yep Student 1
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Density

• Density (d) is the ratio of the mass (m) of a
  substance to its volume (V).
• density mass / volume
• The most common units of density are grams per
  cubic centimeter (g/cm3) or grams per milliliter
  (g/mL).

d m / V
Remember 1 cm3 1 milliliter
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Density Temperature

1. How does temperature affect density?

• Increasing Temperature DECREASES density
•       i.      Volume increases with increasing
  Temperature
• - Why?
•    ii.      Mass stays constant, right?
•     iii.      Since Dm/v D must decrease.
  Why?

- SO DENSITY DEC. WITH INC. TEMPERATURE for
SOLIDS, LIQUIDS OR GAS
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Density and Pressure

1. How does Pressure affect density?

- Solids and liquids are not affected by
pressure - Volume remains constant - No
change in Density

• What happens to gases when pressure is increased?

• Volume decreases but mass remains constant
• Since D m/v D must be increasing

- SO For Gases DENSITY INC. with INC. PRESSURE
(Can you Explain what happens when pressure
decreases?)
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Water is peculiar in that its volume increases
as it goes from liquid At 4 deg To solid at zero.
This is opposite to how most materials behave.
D M/V
D E N S I T Y
As V increases D decreases So ice floats on water
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What is temperature?
- How warm or cold something is - But what does
this mean?
- Molecules are in constant motion - Being in
motion they have Kinetic Energy (K.E. ½ mv2)
  - As they collide with thermometer they impart
their KE to it - Thats why we feel warm or
cold
   - The thermometer molecules begin to move
faster they impart Their energy to the
material inside which warms and expands (or
cools and contracts). We read this change on the
scale.
- So Temperature is a measure of average kinetic
energy!
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Temperature Scales
Fahrenheit (F) - FP is set at 32 and BP is set
at 212
Celcius (C) - FP is set at 0 and BP is set at
100
Kelvin (K) - Absolute Zero is the zero point
FP is then 273.15
One degree on the Celcius scale is exactly equal
to 1 degree on the Kelvin scale
One degree on the Fahrenheit scale is equal to
1.8 degrees on the Centigrade and Kelvin scale
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Conversion formulas
How can we convert from one temperature scale to
another?
K C 273 (more precisely 273.15)
C K 273
Know These !