pH Probes


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Video 1. Harrison demonstrate the pH probe experiment!

- You should be able to describe the pH probe experiment that we did in class. View the above video to review! - JT

pH Scale:


The pH scale is a system that measures how acidic or basic a substance is. The pH scale ranges from 0-14.
The neutral level is seven and anything between seven and fourteen is basic and anything between seven and zero is acidic.
The scale is logarithmic.
Logarithmic means that the levels below seven are ten times more acidic than the value above it and the levels above seven follow suit.
An example of this would be pH 9 and pH 10. pH 10 is ten times more acidic than pH level 9.

"pH Scale." Acids and Bases. unavalible. Elmhurst College. 22 Feb 2007 <http://www.elmhurst.edu/~chm/vchembook/184ph.html>.

- Be able to describe the pH scale as above and be able to explain the relative acidities or alkalinities of various solutions. For example, something with a pH of 4 is 100 times more acid than something with a pH of 6. - JT

phscale.gif

Figure 1. pH Scale with Common Acids
"The pH Scale." VBS page. 06/20/02. VBS. 22 Feb 2007 <http://staff.jccc.net/PDECELL/chemistry/phscale.html>.

Definitions:


pH Probe-Electronic instrument used to measure the pH of liquids

"pH Meter." Wikipedia. Wikipedia Foundation, Inc.. 22 Feb 2007 <http://en.wikipedia.org/wiki/PH_meter>.

pH-a measure of the acidity or alkalinity of a solution. If the pH is less than 7, it is acidic, higher and it is basic. A substance with a pH of 7 is neutral because it is the pH of pure water at 25 degrees c. pH literally means the power of the Hydrogen ions. The "p" comes from the german word for power, potenz. The "H" stands for Hydrogen,explaining why it is capitalized.

Senese, Fred. "What is pH?." Frequent Asked Questions. 21 Sep 2005. General Chemistry Online. 22 Feb 2007 <http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/what-is-pH.shtml>.
"pH." Wikipedia. Wikipedia Foundation, Inc.. 22 Feb 2007 <http://en.wikipedia.org/wiki/PH>.

Acid-a substance that when dissolved in water has a pH less than 7

"Acid." Wikipedia. Wikipedia Foundation, Inc.. 22 Feb 2007 <http://en.wikipedia.org/wiki/Acid>.

Common Acids:
Vinegar (Acetic Acid)
Asprin (Acetylsalicylic acid)
Vitamin C (Ascorbic Acid)
Lemon Juice
Citris fruit (citric acid)
fluids in stomach (hydrochloric Acid),
Batteries (Sulfuric Acid) 4
Carbonic Acid

Nave, "Common Acids." Common Acids. 22 Feb 2007 <http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/acidcom.html>.

- Be able to recognize and or list some common acids. - JT

Common Bases:
Household Cleaners (Ammonia)
Slaked Lime (Calcium Hydroxide
Milk of Magnesia (Magnesium Hydroxide
Soft Soap (Potassium Hydroxide
Drain and Oven Cleaners (Sodium Hydroxide) 4

4"Common Household Acids and Bases." Encarta. 2006. MSN. 22 Feb 2007 <http://encarta.msn.com/media_461535860/Common_Household_Acids_and_Bases.html>.

- Be able to recognize and or list some common bases. - JT

Data:

Number
Name
Prediction
Acid, Base, Neutral
Blue Litmus Paper
Red Litmus Paper
pH from Probe 1
pH from Probe 2
pH from Probe 3
pH from Probe Average
Cabbage Juice
1
Vinegar
Acid
Acid
No Change
No Change
2.91
2.99
3.02
2.97
Pink
2
Soap
Base
Neutral
No Change
No Change
6.8
6.28
6.52
6.53
Lighter Purple
3
CA Water
Neutral
Neutral
No Change
No Change
6.5
7.09
7.3
6.96
Purple
4
Cleaner
Acid
Base
No Change
Blue
9.31
9.26
9.27
9.28
Lime Green
5
Pineapple Juice
Acid
Acid
Red
No Change
4.11
4.11
4.12
4.11
Pinkish Pruple
6
Milk
Neutral
Neutral
No Change
Blue
7.03
7.02
7.01
7.02
Lilac
7
Diet Coke
Neutral
Acid
No Change
No Change
5.63
6.04
3.96
5.21
Pink
8
Amonia
Base
Base
No Change
Blue
9.45
9.44
9.45
9.445
Green
9
Lemon Juice
Base
Acid
Red
No Change
3.22
3.12
3.17
3.17
Pink
10
Milk of Magnesia
Base
Base
No Change
Blue
9.67
9.81
9.86
9.78
Green






















Table 1. Analysis of Household Chemicals

- Review this data table. If you were given data from it, such as, "The solution changes blue litmus paper to red, red l.p. stays red, and finally, the cabbage juice turned green", what does this mean the pH of the solution is? Justify your answer? - JT

Analysis:

Example of pH Probes (Technology)


pH meters range from simple and inexpensive pen-like devices to complex and expensive laboratory instruments with computer interfaces and several inputs for indicator (ion-sensitive, redox), reference electrodes, and temperature sensors such as thermoresistors or thermocouples. Cheaper models sometimes require that temperature measurements be entered to adjust for the slight variation in pH caused by temperature. Specialty meters and probes are available for use in special applications, harsh environments, etc. Pocket pH meter are readily available today for a few tens of dollars that automatically compensate for temperature.

Unknown, Unknown. "pH Meter." Wikipedia. 10 Feb 2007. Wikipedia. 22 Feb 2007 <http://en.wikipedia.org/wiki/PH_meter#The_Probe>.

One type, for example, involves an ion-sensitive field effect transistor (ISFET). These are fairly uncommon today but may become more common in the future. They have the advantage of being more rugged than glass electrodes, and can respond to pH changes much faster. They require power to work, and so require a special power adaptor to use with a normal pH meter. They are also fairly expensive, and not likely to be encountered by hobbyists, except in scientific supply catalogs.

Holmes-Farely, Randy. "Measuring pH with a Meter." Advanced Aquarista's Online Magazine. Unknown. Advanced Aquarista. 22 Feb 2007 <http://www.advancedaquarist.com/issues/feb2004/chem.htm>.

Probes can be used in medicine for evaluation of the flow of acid from the stomach to the esophagus. This method is most commonly used in gastroesophageal reflux cases. The probe determines whether acidic build up is the cause of breathing trouble or other reflux related condtions.

National Jewish Medical and Research Center. "Use of pH Probe Testing." http://www.nationaljewish.org/disease-info/tests/ph-probe.aspx Accessed 22 February 2007.

Pictures


Probe.jpg

Figure 3. An image of a pH probe

"pH Testing." Kittiwake. 2005. Eutech Instruments Pte Ltd Copyright © 1997. 22 Feb 2007 www.kittiwake.com/Default.aspx/Page/KB/KB/236.

external image ph_probe.gif
Figure 4: Another pH Probe

PROGRESSIVE GROWTH HYDROPONICS, "Progress Growth." Garden Supply and Hydroponics. 2/22/2007. 22 Feb 2007 http://www.progressive-growth.com/proddetail.php?prod=45027

Why are pH probes so helpful?
The pH probe is a very accurate way to measure the pH level of a substance. The probe uses a small glass globe to measure the pH value. There are other ways to test pH just as litmus paper and cabbage juice but the probe is most accurate. Logger Pro software is a program that connects to a probe and automatically measures the pH level of a substance.