Water, Strips, Test, reaction, occurs


Question by Stefano:

What reaction occurs with water test strips?

Yeah, what is the reaction between the strips and the water? I know it has something to do with the pads reacting with specific ions of the chemicals, but can I get a more specific chemical equation maybe?




Best answer:

Answer by Tim
An exact chemical equation is hard to give, since zillions of different indicator molecules are used in all the different pH test papers.

Generally, though, indicators of acidity change color when they are protonated and indicators of basicity change colors when they are deprotonated.

These are very specific chemical interactions, then. The indicator will react with whatever the strongest base present in the water, or the strongest acid present in the water, is.

So an equation for an acid indicator might be

H3O(+) + In --> H2O + InH(+)

Since acids generate H3O(+) in water solutions.

Bases generate OH(-) in water solutions, and this is what reacts with test paper. An equation for an indicator that changes color in basic solution would be

InH + OH(-) --> H2O + In(-)

For pretend, if you want to bypass the OH, you can write the equation for the specific base in solution. Say you're using Triethylamine (TEA), a neutral amine with a pKa of about 12 (nice and basic). Go ahead and pretend it does not generate hydroxide ions in solution (in reality, it does) and reacts directly with the indicator instead:

InH + TEA --> TEAH(+) + In(-)

pH test strips that change to one color in acid and another in base simply have two (or more) indicators impregnated into the paper.

Notice that most of the chemical reactions here are NOT complete. They need spectator ions to balance out the charges. harder to visualize in that way though. I'll expand the base equation:

First, TEA reacts with water to make hydroxide ion. The TEA is neutral and the HTEA is a cation, while H2O is neutral and OH is an anion:

TEA + H2O --> HTEA(OH)

Then, the tetraethylammonium hydroxide salt reacts with indicator to make the tetraethylammonium-indicator salt and water. it does this by having the hydroxide deprotonate the indicator to make neutral water. the In on the left is neutral. That on the right is anionic:

HTEA(OH) + In --> HTEA(In) + H2O

That is closer to reality (it reveals these reactions to be the simple metathesis reactions they are) but takes much more typing and it is harder to visualize the charges moving around.

Give your answer to this question below!

Other posts like this, by keyword:

Water:

Shooting & Selling Your Photos: The Complete Guide to Making Money with Your Photography ...
Water Management in Islam (Water Resources Management and Policy Series) Reviews ...
Water Policy in Spain ...
A Drop in the Ocean: The Story of Water (Science Works) ...
Federal Grant supplies Swift Water Rescue Team with new equipment ...
Water Features for Small Gardens: Creating Compact Gardens ...
Could Jesus Walk on Water?: 164 Questions and Answers About the Faith ...
Clues coming in regarding mystery medical pin ...
Ghost Across the Water ...
Water, Ice & Stone: Science and Memory on the Antarctic Lakes Reviews ...
Strips:

The 2009 Import and Export Market for Iron or Steel Nails, Tacks, and Staples Excluding Staples in Strips for Office Use and Articles with C ...
The 2011 Import and Export Market for Copper Nails, Tacks, Drawing Pins, Staples, Screws, Bolts, Nuts, Screw Hooks, Rivets, and Washers Excl ...
The 2010-2015 Outlook for Blood Glucose Meters and Strips in Europe ...
The 2011 Import and Export Market for Natural Rubber in Primary Forms, Plates, Sheets, or Strips Excluding Latex in Japan ...
Building with Nature: Inspiration for the Arts and Crafts Home ...
The 2009 Import and Export Market for Iron or Steel Nails, Tacks, and Staples Excluding Staples in Strips for Office Use and Articles with C ...
The 2011 Import and Export Market for Copper Nails, Tacks, Drawing Pins, Staples, Screws, Bolts, Nuts, Screw Hooks, Rivets, and Washers Excl ...
The 2011 Import and Export Market for Aluminum Nails, Tacks, Staples, Screws, Bolts, Nuts, Rivets, and Washers Excluding Staples in Strips f ...
What are the best whitening strips that will work within 3 days? ...
Fan GraphiX Number 2 Science Fiction-fantasy, Stories, Articles, Strips, Humor ...
Test:

Essential AP Biology (flashcards) (College Test Preparation) Reviews ...
Testing Top Guns: United States Air Force and Navy Test and Evaluation Squadrons Reviews ...
What are some great books to prepare for my speaking test? ...
Cracking the AP U.S. History Exam, 2009 Edition (College Test Preparation) ...
Officer Candidate 6e (Arco Military Test Tutor) Reviews ...
WEST-E Designated World Language: Spanish 0191 Teacher Certification Test Prep Study Guide (Xam West-E/Praxis II) Reviews ...
Barton facing fitness test ...
Case Closed. A Detective Story Set in Zimbabwe Reviews ...
Gale Encyclopedia of Cancer: Fecal occult blood test ...
How come i never had a positive pregnancy test before? ...
reaction:

Architecture and Computers: Action and Reaction in the Digital Design Revolution ...
occurs: