MICROLAB™ AND CALIBRATION CURVES

Lab 6

Outline

o Computer Etiquetteo Calibrations and Calibration Curveso MicroLab Probe Calibrationo MicroLab Data Analysiso Significant Figures and Graphingo Data for your In-class Assignmento Slope and Y-intercept – Significant Figureso What you need to turn in todayo Lab 7 Remindero In-class Assignment

Computer Etiquetteo Do not surf the webo Do not check your e-mail unless it’s related to this

courseo Do not print materials unrelated to labo Do not connect a USB mass storage driveo No social networking!!!o Do not open any attachments, unless directly from

your lab Blackboard shell or lab instructor e-mail.o You may access Blackboard from your lab computer

once given permission.

Calibrations and Calibration Curves

Two types: Standard curves – to determine an instrument’s response

to a given analyte under a specific set of parameters (you worked with two of these in your homework assignment)

Internal calibration curves – to convert between a probe / instrument’s native input and our required output (you will be making up one of these today)

MicroLab pH Probe Calibrationo pH probes require calibration in order to convert between their native

input (unit measured by the instrument, mV) and our required output (unit we are required to measure or report, pH). This type of calibration is referred to as an internal calibration.

o Your instructor will now show you how to calibrate a MicroLab pH probe after which you will have an opportunity to practice.

o You can follow along with the instructions on p. 178 in your lab manual.

o Make sure your interface is turned on BEFORE you access MicroLab on the computer.

o After you have finished your pH probe calibration and printed your graph, exit out of MicroLab.

o Use your printed calibration curve to answer the “MicroLab™ Calibration Exercise” questions on your report sheet on p. 185.

Significant Figures and Graphing

• Most of the data you work with in this lab will have a linear curve fit.

• Once you determine the equation for the line, the significant figures of the slope and the digits of precision of the y-intercept need to be determined.

• We limit these values when we copy down the equation, or when we use the values for the slope and y-intercept in an equation.

Significant Figures and Graphing

• When determining the significant figures / digits of precision to use for your equation, look only at the non-zero data points in your data table.

• Your y-intercept is limited to the same digits of precision as the values plotted on your y-axis.

• Your slope is limited to the same number of significant figures as your data point with the fewest number of significant figures.

Example Data

Conductivity, S/cm Potential Difference, V

0.0 0.00

720.0 0.18

1390.0 0.32

3300.0 0.73

6130.0 1.33

8400.0 1.82

Slope and Y-intercept

When you plot the data from the previous table, you find that the resulting graph has a linear curve fit. For the resulting equation:

How many significant figures should the slope have?

How many digits of precision should your y-intercept have?

Remember this concept when you complete your in-class assignment today!

What to turn in today:

After you are finished today:

Make sure all questions have been answered. Submit today:

Lab 6 report along with:• pH probe calibration curve• Spreadsheet for your in-class assignment• Graph for your in-class assignment

Make sure your name and section number are on the front page.

Lab 7 Reminder

• Read the required reading sections in your textbook and lab manual.

• Complete and submit the pre-lab questions by the deadline. Complete the molar mass significant figure tutorial

in Blackboard before attempting the molar mass calculations.

Use the periodic table in the lab manual.

Study for the quiz.

In-class assignment

See the “In-class” Presentation.