### MicroLAB* Homework

```MicroLAB™ and
Calibration Curves
Lab 4 Pre-lab Help
MicroLAB™
 MicroLAB™ is a computerized system that
allows us to acquire real-time data.
program with data analysis tools.
 Your lab manual has the instructions for the
completion of this exercise.
 Double check your work onscreen before
printing out anything.
Pitfalls
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Always type a “0” before a decimal point for
numbers smaller than 1, e.g. 0.123.
Label columns correctly the first time. If you don’t,
you will have to delete and redo them, which will
result in a loss of data.
If you are told to label a column [Fe], M the “[Fe]”
refers to the label and the “M” the unit. If there are
no units present, then that variable does not have
any units.
More Pitfalls
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Do not give two columns the same label.
Do not label a column for which you will need to
create a formula.
The digits of precision you set your column
properties to should reflect the digits of precision of
Select “Accept Data” often!
When asked to look at a graph to determine certain
values, always reference the spreadsheet for the
Label / Variable
Graphing
Graphing is an important
tool used to represent
relationships in
experimental outcomes and
to set up calibration curves.
It is a modeling device.
meaning of the labels /
variables yet. You will get
to know these as the
semester progresses.
Let’s look at the following
data:
Units
[Ni2+], M
Absorbance
0.200
0.041
0.300
0.063
0.400
0.085
0.500
0.101
Graphing
Graph Title
Absorbance vs. [Ni2+], M
Absorbance
Equation
0.110
0.100
y = 0.20 x + 0.002
0.090
0.080
0.070
0.060
Best-fit Line
0.050
0.040
0.200 0.250 0.300 0.350 0.400 0.450 0.500
Graph Axis Labels
[Ni2+], M
Graphing
slide, the title was
Absorbance vs. [Ni2+], M
because absorbance was graphed on the y-axis
and [Ni2+], M was graphed on the x-axis.
(Always y vs. x!)
If a graph title is
Temp F, degrees F vs. Temp C, degrees C
what should be graphed on the x-axis?
Graphing
Always label your axis appropriately. The label for
the y-axis is Absorbance. Absorbance has no
units, so none are listed. The label for the x-axis is
[Ni2+] and the units M. What does “M” stand for?
If an axis is labeled with Temp F, degrees F
which one is the unit?
Graphing
If your data points look like they fall on a line, be
sure to add a “linear” calibration curve to them. If
they don’t appear linear, DO NOT add a linear line.
When you add a regression line to a set of data
points, an equation results. This equation
values. The equation on our graph was:
y = 0.20 x + 0.002
Equation
 y = 0.20 x + 0.002
(y = mx + b)
 The number (and sign) before the “x” is called
the slope of the line (m).
 The number (and sign) without the “x” is
called the y-intercept of the line (b).
 If a value is substituted in for x, do you know
how to solve for y?
 If a value is substituted in for y, do you know
how to solve for x?
Calibration Curves
 A calibration curve gives you a graphical
representation of an instrument’s response to a
particular analyte.
 If we were to declare your 1992 Ford Escort an
“instrument” and the gas it uses an “analyte,” we
could construct a calibration curve for:
Distance Driven, miles vs. Gas Consumed, gallons
Calibration Curves
 The measurements that are made should all
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with the same vehicle
using the same set of tires
driving under similar road and environmental
conditions
using the same type of gas
Data Table of Standards
Distance Driven, miles
Gas Consumed, gallons
25.3
1.0
49.2
2.0
73.9
3.0
98.2
4.0
122.8
5.0
Calibration Curve
Distance Driven, miles vs. Gas Consumed, gallons
Distance Driven, miles
140.0
y = 24 x + 0.7
R2 = 1
120.0
100.0
80.0
60.0
40.0
20.0
0.0
0.0
1.0
2.0
3.0
4.0
5.0
Gas Consumed, gallons
Notice that the average gas consumption of this vehicle is 24 mpg!
Unknowns
 Unknown analyte refers to an unknown measurement, not an
unknown identity.
 To analyze three unknowns related to our previous
example…we know we will be analyzing gas, the unknown
measurement refers to either the gallons of gas consumed,
or the distance driven.
 No matter which unknown we are trying to determine, our
analysis must be made under the same conditions as
previously so that we don’t introduce new variables. Do you
remember what they were?
Data Table of Unknowns
Distance Driven, miles
Gas Consumed, gallons
41.5
?
82.1
?
103.6
?
Calibration Equation
 Use the previously determined calibration
equation to determine how many gallons of gas it
would take to drive the number of miles indicated
on the previous slide.
 Since Distance Driven was plotted on the y-axis
and Gas Consumed was plotted on the x-axis,
the new equation becomes:
Distance = 24 (Gas Consumed) + 0.7
Calibration Equation
Distance = 24 (Gas Consumed) + 0.7
Let’s solve this equation for Gas Consumed:
Gas Consumed = (Distance – 0.7) / 24
Solving Unknowns
Gas Consumed = (Distance – 0.7) / 24
Substitute in the measured values:
Gas Consumed = (41.5 – 0.7) / 24
= 1.7 gallons
Gas Consumed = (82.1 – 0.7) / 24
= 3.4 gallons
Gas Consumed = (103.6 – 0.7) / 24
= 4.3 gallons
Hand-Entry Template
 After you access MicroLab™ (in one of the
computer labs or on your computer) do the
following:
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In the dialogue box that tells you the
MicroLab™ hardware could not be found, click
on “Hand Enter / Simulate”
Click on the “Hand Enter” tab.
Open the “MicroLab Experiment” file.