Online Lab Submission
Students: Instructors: Virtual Labs: Pre-Lab Assignments
Interactive Animations:

Graphical Display of Lab Data

There are a variety of chemistry labs that use sophistocated instruments to collect data at certain time intervals. These experiments can quickly amass large data sets that are difficult to interpret unless displayed graphically. The four graphs below illustrate the unique features of the Chem21Labs graphing application.


Titration Curve (Weak Acid)

Pressure vs. Time Curve

The pH vs. mL NaOH added graph reveals that the weak acid is diprotic with two inflection points and two pka's. The online lab report sheet receives this pH data via 1) manual entry, 2) copy/paste the pH meter x,y data into a text area, or 3) automatic upload from the pH meter to the Chem21Labs server.
Once the data is saved to the server, the Chem21Labs program uses the data to calculate the pH at the inflection points, the pka values and the corresponding x values (mL of NaOH added) before the graph is displayed on the webpage. When the student enters any of these values, their entry is automatically graded.
In addition to graphing pH vs. mL NaOH, pressing the 1st Derivative and 2nd Derivative buttons at the top of the graph will graph the corresponding derivative of the data.

The decomposition of H2O2 is studied by recording the pressure as a function of time.

H2O2 (aq) → H2O(l) + O2 (g)

At the beginning of this kinetics experiment a plunger is withdrawn from a syringe to lower the pressure. As O2 forms from the decomposition, the pressure increases. Once the pressure reaches atmospheric pressure, the plunger is withdrawn 2 mL. This process is repeated for 8 readings. After lab, students mouseover the data points to determine the precise time that it took for the O2 pressure to reach atmospheric pressure each of the 8 times. This information is used to determine the rate law.

Freezing / Melting Curve

Absorbance vs. Wavelength

Multiple freezing points are collected in a freezing-point depression / colligative property lab with a temperature probe. After lab, students use the Chem21Labs graphing application to draw lines on the graph as shown. The intersection of the two lines is the freezing point for Trial 1.

The Chem21Labs graphing application can display up to 7 sets of data on a single graph. The Absorbance vs. Wavelength of an indicator was measured at 7 different pHs and the stacked plot quickly shows the pH at which the indicator absorbed the most yellow light (λ = 550 nm).