In an effort to help you and your students better understand spectrometer absorbance readings, we’ve collected a few commonly asked questions:
Why don’t absorbance readings have units?
Absorbance readings are unitless because they are calculated from a ratio of the intensity of light transmitted through the sample (I) to the intensity of light transmitted through a blank (Io). This ratio results in a unitless value.
Absorbance = log (Io/I)
Why are absorbance readings most accurate between 0.1 and 1?
Remember that absorbance is the logarithm of the transmission of light through a sample. Transmission (T) is the ratio of the intensity of light transmitted through the sample (I) to the intensity of light transmitted through a blank (Io). Therefore, absorbance = log (Io/I).
At an absorbance of 2 you are at 1%T, which means that 99% of available light is being blocked (absorbed) by the sample. At an ABS of 3 you are at 0.1% T, which means that 99.9% of the available light is being blocked (absorbed) by the sample. Such small amounts of light are very difficult to detect and are outside the meaningful range of most spectrometers.
Vernier array spectrometers and colorimeters have a useful absorbance range between 0.1 and 1.0. Any absorbance reading above 1 can be inaccurate. There are spectrometers that will report meaningful values at absorbance ranges above 1.0, but these are research instruments that are also quite expensive. In most classroom settings, the best option is to simply dilute your samples to ensure they are in this range.
How important is it to use a quartz cuvette for absorbance readings in the UV?
It depends on how accurate you want your absorbance readings to be. UV plastic cuvettes are less expensive and have practical applications when working with students, but they lose transparency quickly in the UV. Most are only rated to 280 nm. If you want the most accurate data possible below 280 nm, a quartz cuvette is the best option. Another unfortunate side effect of using UV-plastic cuvettes is that students commonly confuse them with visible-only plastic cuvettes. This cuts out all UV light, so data will be very poor. If you are going to use UV-plastic cuvettes, make sure you are using them for the proper applications.
Are you a member of the American Chemical Society (ACS)? I’ve been a member for 10 years and currently serve as the Secretary for the local Portland Section. ACS is a scientific society of chemistry professionals that includes students, educators, and industrial chemists.
Each year ACS hosts two national meetings; one in the spring and one in the fall. The national meetings offer the opportunity to discover and share knowledge through posters, presentations, and training workshops. The expo features hundreds of exhibitors showcasing new technological developments. The ACS Career Fair at the national meetings offer access to ACS career consultants and a career fair for job seekers and employers. I found my current career here at Vernier Software & Technology through the ACS Career Fair.
There are also several regional meetings that are organized by ACS Local Sections. These meetings also feature technical programs on a variety of topics, poster sessions, expositions, and social events. The smaller size of an ACS regional meeting allows for a greater opportunity for interactions and costs less to attend than a national meeting. Take advantage of the opportunity to attend a regional meeting.
I attended the Northwest (NORM) Regional Meeting from June 24–27 on the campus of the Pacific Northwest National Lab in Richland, WA. The theme was Powering the Future: Energy, Environment, Education. I co-presented a talk with Prof. Karen Goodwin from Centralia College about Data Acquisition in the Chemistry Lab. It highlighted the benefits of using data logging for several common general chemistry experiments such as gas laws, acid-base titrations, and electrochemistry. Our goal was to show that using data-acquisition tools results in fewer possibilities of transcription errors and combines the power of graphical visualization and mathematical data analysis.
My next talk will be at the Fall National Meeting that takes place in Boston, Aug 19–23, 2018. I will be presenting a talk on using kitchen chemistry and technology to engage K–12 and college students. I hope to meet you there. If you are interested in attending, here are the details.
PAPER TITLE: Using kitchen chemistry and technology to engage K–12 and college students (CHED 137)
DAY & TIME OF PRESENTATION: Monday, August, 20, 2018 from 3:45 PM–4:05 PM
ROOM & LOCATION: Cambridge 1/2 – Seaport World Trade Center
Did you know that you really can’t calibrate a Vernier Drop Counter? Instead, you are actually calibrating the tip of the titrant reservoir.
The Vernier Drop Counter is a modified photogate designed, through the software, to monitor drops of liquid as they pass through the slot. A beam of infrared light passes through the slot continuously. If anything blocks that beam, the software interprets that as a drop. The result is either a drop, or no drop.
More accurately, when you calibrate a Vernier Drop Counter, you are determining the drop size for titrants as they are delivered from the reservoir tip. The drop size will vary depending on the composition of the titrant, the intermolecular forces between the molecules of the titrant and the plastic in the tip, the height of liquid in the reservoir, the rate at which the drops are allowed to flow out of the tip, and even the temperature. The tip is made of formed plastic. The drop size will also vary with different tips.
For the absolute best results, different titrants should be calibrated individually. For aqueous solutions with concentrations of 1 M or less, a reasonable calibration of the Vernier Drop Counter can done with distilled water at room temperature. While the software is running, drops are allowed to pass through the slot in the Drop Counter, collected in a graduated cylinder, and counted by the software. A drip rate of around 1 drop every 2 seconds is recommended to allow the drops to reach their maximum size. (This also allows the pH, conductivity sensor, or oxidation/reduction potential sensor time to react between drops.) It is recommended that the reagent reservoir be filled to 60 mL and a total volume of just under 10 mL be collected during the calibration. This ensures that the pressure on the drops at the tip is reasonably constant. The larger the volume of titrant used and number of drops, the more accurate the value for the drop size.
Once a prescribed volume of water is collected, the valve is closed, the volume is entered into the software, and the value of drops/mL is calculated automatically. This value can be written on the reservoir system (reagent reservoir, valves, and tip) for future use. All Vernier software allows the user to enter the known value without having to completely carry out the calibration again.
Vernier Tip: Check out our Thingiverse webpage for a free, 3D-printable design for a widget that centers the reagent reservoir system above a Drop Counter. It comes in handy for aligning the tip to ensure the drops are detected by the Drop Counter.
Collect sound data wirelessly with the snap of your fingers. With sound-triggered data collection, Go Direct® Sound provides students with an easy way to capture and evaluate waveforms. Measure wave amplitude and sound intensity level at the same time to investigate the decibel scale, or take the sensor outside the classroom to discover sounds in their natural environment.
An Oxidation Reduction Potential (ORP) Sensor measures the activity of oxidizers and reducers in an aqueous solution. It is a potentiometric measurement from a two-electrode system similar to a pH sensor. Sometimes it is also referred to as a redox measurement. Unlike a pH sensor, an ORP sensor measures the ratio of oxidized to reduced forms of all chemical species in solution.
The ORP sensor is made up of two electrochemical half cells where the reference electrode is generally Ag/AgCl and the measurement electrode is commonly Pt. The potential difference between the two electrodes represents the redox potential of the solution being measured and can be described by the Nernst equation.
E = Eo – 2.3 (RT/nF) x (log [Ox] / [Red])
E = total potential developed between the measurement and reference electrodes
Eo = a voltage specific to the system
R = gas constant
T = temperature in K
n = the number of electrons involved in the equilibrium between the oxidized and reduced species
F = Faraday constant
[Ox] = concentration of the oxidized species
[Red] = concentration of the reduced form of that species
The output of the ORP sensor is relative to the reference electrode. For example, a reading of +100 mV indicates the potential is 100 mV higher than the potential of the reference half cell and suggests an oxidizing environment. Likewise, a –100 mV reading indicates a potential 100 mV lower than the reference half cell and is a reducing environment. In some applications, redox potential may be reported as Eh which is the voltage reading with respect to the Standard Hydrogen Electrode (SHE). By taking into account the offset of the reference electrode used in the ORP sensor, the potential can be converted into Eh readings. Vernier ORP sensors use a Ag/AgCl saturated KCl reference electrode.
In education, a common application for an ORP sensor is a potentiometric titration. Similar to an acid-base titration, a titrant is added to a sample incrementally until all the sample has reacted and the end-point is reached. One example where students can apply their understanding of redox is by using a Vernier Go Direct ORP Sensor to determine the concentration of H2O2 by titrating the solution with KMnO4. To correctly calculate the concentration, students must understand the balanced redox reaction between KMnO4 and H2O2.
Vernier Tip: Check out two additional experiments from Vernier using an ORP Sensor.
We’re very excited about this release as it includes support for photogates in the most common modes of motion, gate, and pulse timing. It is also the first release of the Android version, which adds support for Go Direct® sensors!
Tangent line analysis feature
Support for Photogate when used with LabQuest interfaces (not yet available on Android)
Lithuanian language support
Android platform now has the same user interface as macOS, Windows, and ChromeOS
Interface can be scaled for larger font size and thicker graph traces
“The mobility of the Vernier Go Direct® Motion Detector opens up new channels of scientific inspection. Of course there is the highly accurate and fast motion detection, but there is also the ability to easily navigate materials and angles, and interference, and most anything else one can think of at the intersection of the Vernier Go Direct® Motion Detector and sound material science (pun intended).”
And, he concludes by saying:
“The word echo, by the way, stems from the story in Greek mythology about a cursed nymph who was doomed to only repeat the last words anyone spoke to her. My guess is today’s students will echo each other when using the Vernier Go Direct® Motion Detector by repeating single words over and over like, “Cool” and “Wow!””
The complete Go Direct family of sensors offers teachers and students maximum versatility to collect scientific data either wirelessly or via a USB connection. These low-cost sensors can be used in more than 300 teacher-tested experiments developed by Vernier and are supported by free graphing and analysis software, the Graphical Analysis™ 4 app.
To inspire students to learn about renewable energy and hone their engineering skills, Vernier supported the 2018 KidWind Challenge, hosted by the KidWind Project. The challenge consists of dozens of local and regional competitions across the country, called KidWind Challenges, during which teams of students test the energy output of wind turbines they design and build. Students also present their design processes to a panel of judges and participate in short design or problem-solving tasks called “Instant Challenges.”
Teams that take top place at local challenges are invited to the National KidWind Challenge. This year, almost 300 students in grades 4–12 from across the country traveled to Chicago, Illinois, for the National KidWind Challenge on May 8–10, 2018. The event, held during the American Wind Energy Association (AWEA) WINDPOWER 2018 Conference & Exhibition, hosted a total of 21 high school and 40 middle school teams competing for the chance to win the grand prize of $750, the second place prize of $500, and the third place prize of $250.
The 2018 National KidWind Challenge Champions are
High School Division:
First Place – Redwood Express from Bath County High School in Hot Springs, Va.
Second Place – Tuttle Windy’s from Tuttle High School in Tuttle, Okla.
Third Place (Tie) – Silver Bullet from Coachella Valley High School in Thermal, Calif.
Third Place (Tie) – iTurbine X from Old Donation School in Virginia Beach, Va.
Middle School Division:
First Place – Oxford Air Sharks from Oxford Middle School in Oxford, Kan.
Second Place – SPINNERS from Lanier Middle School in Fairfax, Va.
Third Place – The Birds from Darlington Elementary-Middle School in Darlington, Wis.
The Vernier Total Solar Eclipse Campaign recently won a 24th Annual Communicator Award of Distinction in the Integrated Campaign—Business to Consumer category. The campaign was recognized for successfully demonstrating one theme through various forms of media, such as print, social media, video, and more.
With entries received from across the United States and around the world, the Communicator Awards is the largest and most competitive awards program honoring creative excellence for communications professionals. The awards are judged and overseen by the Academy of Interactive and Visual Arts (AIVA), a 600-plus member organization of leading professionals from various disciplines of the visual arts.
The multi-pronged Vernier Total Solar Eclipse Campaign celebrated last summer’s Great American Eclipse by providing tips, resources, and data that STEM teachers could use to teach students about the real-world physical phenomenon throughout the year. Examples of the data collected by educators using Vernier technology are available for free on the Vernier website. Sample data by Dave Vernier was also included in an article about the eclipse in The Physics Teacher.
In addition to the Communicator Award, the Vernier Total Solar Eclipse Campaign also won a One Planet Award and two Stevie® Awards.
The Vernier Total Solar Eclipse Campaign recently won two Stevie® Awards in the 16th Annual American Business Awards®. The campaign won a bronze in both the Branded Content Campaign of the Year and Small-Budget Marketing Campaign of the Year (<$3 million) categories.
This year’s awards program received more than 3,700 nominations from organizations of all sizes and in virtually every industry. More than 200 professionals worldwide participated in the judging process to select the winners.
The Vernier Total Solar Eclipse Campaign celebrated last summer’s Great American Eclipse by providing tips, resources, and data that STEM teachers could use to teach students about the real-world physical phenomenon throughout the year. Examples of the data collected by educators using Vernier technology are available for free on the Vernier website. Sample data by Dave Vernier was also included in an article about the eclipse in The Physics Teacher.