2.4: Vernier Probes
- Page ID
- 476996
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Temperature Probe
The temperature probe is plug and play with three base modes (meter, graph and table). To calibrate it you need to use Logger Pro and will need to make measurments at three different temperatures. Students will not need to calibrate these.
Figure \(\PageIndex{1}\): LabQuest2 showing three display modes for temperature, meter (left), graph (center) and table (right). (R.E.Belford; CC0)
pH probe
Download Vernier pH probe manual
Multiple labs this semester will be using a pH probe In this class we will use Vernier's pH probes that can be directly connected to a LabQuest, or if we use the Go!Link we can connect them to the USB port of a laptop or Raspberry Pi.
Figure \(\PageIndex{2}\): pH probe on left set up to a Raspberry Pi microcomputer. Apparatus on right shows setup for titration, note stirring bar is under burette and located so it does not touch probe while spinning. (Copyright; Bob Belford CC-BY)
In this experiment we will use a Ph probe, which is an electronic device that measures the pH. These are very common and they should always be checked against standard solutions of known pH and calibrated if they read incorrectly. The pH probe is an electrochemical cell and we will cover these in chapter 19, sections 19.3-19.5 and 19.7. The following YouTube from Oxford Press does an excellent job of describing how a pH probe works. It is imperative that you test your probe in a buffer to be sure it is reading accurately and if it is not, you will need to calibrate it.
Video \(\PageIndex{1}\) 2:30 YouTuve describing the operation of a pH probe developed by Oxford University Press (https://youtu.be/aIn4D2QXUy4).
The pH reading is not accurate until the probe stabilizes, so when you change the pH you need to wait until the reading becomes steady before recording the value.
General Instructions for use of a pH meter
The pH probe is stored in an electrolyte and should never be allowed to dry out. You should have DI water in a squeeze bottle that you can rinse the probe tip over a 600 mL beaker and be careful to never touch the probe surface. Between measurements you can fill a keep the probe in a 150 mL Erlenmeyer flask that is half full of water (this is more stable than a beaker). The first thing you should do is test your probe with a small amount of buffer solution solution of known pH and if it reads the buffer pH accurately, you are good to go, and if not, you need to calibrate the pH meter before proceeding.
Figure \(\PageIndex{3}\): Checking probes with buffer solutions. (Copyright; Bob Belford/Liliane Poriot CC-0)
Calibration
Drop Counter
Download Vernier Drop Counter Manual
Water absorbs infrared light. The drop detector uses an IR LED to emit a beam of light that is directed at a photodetector which reads a voltage as long as the light is hitting it. The apparatus is set up so that when a drop of titrant falls from the burette it interferes with the light beam and photodetector voltage goes to zero while the drop travel through the IR beam, and then returns to its normal voltage value. This event functions as a software trigger. When calibrating the probe this causes a digital counter to increase by a value of one, which is used to calculate the volume of each drop. When collecting data this sends to a data file the pH (dependent variable) while incrementing the volume (independent variable) by the volume of one drop.