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.
What’s the calibration
3
source
Capacity = ? 100 ml
source
Calibration = ?
1 ml
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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
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estimated value as well as the numbers 1-9.
67.4 ml
Estimated value
source
Calibration = ?
1 ml
source
6
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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What’s the calibration?
Meter Stick
source
On this meter stick, the
closest lines are 1 millimeter
or 0.001 meter apart.
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What’s the calibration?
0.1 gram
What can we estimate to?
0.01 gram
Triple beam balance
What’s 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.
What’s The
calibration? 0.1 ml
source
What’s the reading?
21.35 ml
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PERCENT ERROR
Now Let’s look at at a set of experimental B.P.
Data collected by two students:
Student 1
76.5 deg C
76.1
76.6
76.9
Student 2
78.0 deg C
78.4
77.9
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
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Of data is more accurate?
Percent Error
The data for student 1 “looks” better but how
much better was that data than student 2’s data?
To make this comparison we need to look at
the % error for each student’s set of data
Formula for % ERROR:
Experimental Value – Accepted Value
Accepted Value
x 100
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Problem:
If student 1’s Exp. Value was 76.5 and the Accepted value
Is 77.2 what is her experimental error?
Student 1:
76.5 - 77.2
77.2
x 100. = - 0.907% Error
Student 2:
78.1 - 77.2
77.2
x 100. =
1.17% Error
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
d=m/V
• 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).
Remember … 1 cm3 = 1 milliliter
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Density & Temperature
1. How does temperature affect density?
a. Increasing Temperature DECREASES density
i.
ii.
iii.
Volume increases with increasing Temperature
- Why?
Mass stays constant, right?
Since D=m/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?)16
Water is peculiar in that it’s 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
- That’s 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 !
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