Lab 4

o Do not surf the web o Do not check your unless it’s related to this course o Do not print materials unrelated to lab o Do not connect a USB mass storage drive o No social networking!!! o Do not open any attachments, unless directly from your lab Blackboard shell or lab instructor . o You may access Blackboard from your lab computer once given permission.

 Two types:  Standard curves – to determine an instrument’s response to a given analyte under a specific set of parameters (you created two of these in your pre-lab 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)

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.

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.

Conductivity,  S/cm Potential Difference, V

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!

 Follow the instructions starting on page 134 to create your own hand-entry spreadsheet and graph.  Perform a calibration analysis.  The data to use will be introduced shortly.

o 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 You will now be shown how to calibrate a MicroLab pH probe after which you will have an opportunity to practice.

 Follow the instructions starting on page 135 to calibrate your pH probe.  Perform a calibration analysis.

 Read the required reading sections in your textbook and lab manual.  Complete and submit the pre-lab questions by the deadline.  Question 4 will need to be completed in MicroLab™ in the SCICom lab, Chemistry Resource Center or on your computer if you downloaded the program. Plan accordingly.  Submit your Lab 4 Report  Study for the next quiz.