pH Sensor
Experiment Guide
pH Sensor
Introduction:
Part of the Eisco series of hand held sensors, the pH sensor allows
students to record and graph data in experiments on the go.
This sensor can be used to measure the static pH values of common
liquids (water, milk, soft drinks, vinegar, etc.) as well as the changing
values in titrations or experiments such as those looking at the effect
of antacids.
The pH sensor is designed for long life in a variety of general purpose
situations. Its sealed reference system and gel fill make it easy to use
and maintain. With an epoxy body it is a durable electrode for use
both in the laboratory and in the field.
Sensor Specs:
Range 0 - 14 | 0.01 pH resolution | 100 max sample rate
Activity – pH of Common Household Chemicals
General Background:
Acids are chemical substances whose aqueous solutions have a higher concentration of
positive Hydrogen ions (H+) in the solution. The opposite substances of acids are bases,
whose aqueous solutions have higher concentrations hydroxide ions (OH-).
We measure the relative acidity or basicity using a scale called the pH scale. The scale
goes from 0 to 14, where 7 is the neutral point and has the pH of water. Chemicals that
are acidic have a pH below 7, and bases are above 7.
The pH scale is a logarithmic scale, which means that when going from a chemical that
has a pH of 8 to a pH of 9, the more basic substance is not a factor of 1 times more
basic, but a factor of 10. A pH of 10 is a factor of 10 higher than the substance with a
pH of 9, and so on. Thus the chemical with a pH of 10 is 100 times more basic than the
chemical with a pH of 8 (as 10×10 = 100).
In your kitchen, or under the sink in your bathroom, you’ll find many substances and
chemicals that have a non-neutral pH, and thus are acids or bases. In this activity we’ll
discover the pH for several chemicals and determine their relative strength.
Required Materials:
Eisco pH Sensor & Handheld Unit
Eisco Basic Lab Supply Pack [CH0871] (test tubes, test tube rack, wash bottle, 250 mL
beaker, 400 mL beaker, 10 mL graduated cylinder, 250 mL graduated cylinder)
6 various chemical substances (such as powdered detergent, baking soda, soda, milk,
lemon juice, vinegar, tap water)
Distilled water
pH 7 Buffer solution
Masking tape
Procedure
1. Before performing the activity, a teacher should prepare the various solutions for
the students. Prepare 200 mL of each solution to test in a 250 mL graduated
cylinder. For the baking soda, prepare a 1% solution (2 g of NaHCO3 per 200mL
solution). Similarly for the powder detergent, prepare a 1% solution (2 g of solid
detergent per 200 mL solution. Have approximately 250 mL of distilled water for
each lab group. Prepare 50 mL of pH 7 buffer solution each lab group.
2. With the masking tape, label each one of the test tubes with the numbers 1-6.
3. Fill your wash bottle with about 250 mL of distilled water.
4. Fill your 250 mL beaker with 50 mL of pH buffer solution.
5. For the first prepared solution, carefully pour 5 mL of solution into your 10 mL
graduated cylinder. Pour into the first test tube. Place in test tube rack. Record
in the table the name of solution one.
6. Carefully fill each of the remaining five test tubes with a sample of each solution
to the same height as the first test tube. Record in the table the name of each
solution.
7. Remove the pH sensor from the storage solution container. Rinse with distilled
water from the wash bottle over the empty 400 mL beaker. Let drip dry.
8. Turn on the Eisco pH Sensor. We need to calibrate the sensor before testing the
pH of the solutions. To do so, place the head of the pH sensor in the pH 7 buffer
solution, and on the head unit, set this as the reference pH through accessing the
calibration menu by pressing the upper right of the touch screen where it reads
‘pH’. Now your pH sensor is properly calibrated.
9. Remove sensor from buffer. Allow to drip dry.
10. Place the head of the pH sensor into the first test tube. Record the pH in the
appropriate place in the table.
11. Remove the pH sensor from the test tube. Allow to drip dry. Using the wash
bottle, rinse off any remnant liquid over the 400 mL beaker. Allow to drip dry.
One may recalibrate the pH sensor by repeating the instructions in step 8 at this
point.
12. Place the head of the pH sensor in the second test tube. Record the pH in the
appropriate place in the table.
13. Continue for the solutions for the remaining test tubes. Be sure to rinse the
sensor head as instructed in step 11 between each measurement so as to not
contaminate the following solutions. Record the pH measurements in the
appropriate spots in the table.
14. After recording the last pH, again clean the sensor head as instructed in step 11.
Allow to completely dry. Replace sensor head in storage solution container to
ensure pH sensor’s long life.
15. Dispose of the solutions in the test tubes and beakers as instructed by the
instructor.
Data
Number
Name of
Solution
pH
1
2
3
4
5
6
Questions
1. Which of the tested solutions were acids? Which were bases?
2. How many times more basic is a pH of 11 than a pH of 8? How many less times
acidic is a chemical with a pH of 4 than a pH of 2?
Sample Results
These are examples of possible results. Due to the many variables involved, exact
reproduction is unlikely, but students should find similar results.
Number
Name of
Solution
pH
1
Vinegar
2.2
2
Lemon Juice
2.5
3
Soda
3.0
4
Milk
6.4
5
Baking Soda
8.4
6
Powder
Detergent
9.2
Answers to Questions
1.
Any solution with a pH below 7 is acidic. Possible tested acids are vinegar,
lemon juice, and soda. Any solution with a pH above 7 is basic. Possible tested
bases include milk, baking soda, and powder dishwasher detergent. The
solutions in the table are listed in increasing pH, from most acidic to most basic.
2.
A pH of 11 is 1000 times more basic than a pH of 8 (10×10×10 = 1000). A pH
of 4 is 100 times less acidic than a pH of 2 (10×10 = 100).