Qualitative pH Test Strips

  • Chlorophenol Red (CPR) test paper is useful in differentiating between a solution with an acidic pH and one with a more neutral pH. The unreacted paper is yellow/orange in color. At neutral pH (about 6.7) the paper will turn a reddish color. At higher pH values, the paper will turn more violet. Given that the paper starts out yellow/orange and turns red at roughly the pH of water, it is useful in finding water leaks.
  • Bromophenol Blue (BPB) test paper is useful in differentiating between a solution with an acidic pH and one with a more neutral pH. At pH 3.0 and lower, the paper will be a yellow/green color. Above pH 4.6, the paper will remain blue (it is blue when unreacted). This paper can be used to monitor acid washes (yellow/green) and subsequent rinse waters (blue). This paper can also be used to monitor a pickling process where the pH (acetic acid or vinegar) of the solution must be below 4.6.
  • Blue Litmus test paper is a foolproof pH test to determine if something is acidic. The Blue Litmus test paper does not come with a color chart as it cannot provide you with a defined pH value. The test strip will turn red if dipped into an acidic solution (pH <7). It will remain unchanged in an alkaline solution. Although there is no color chart, the strip will turn various shades of red, getting darker the more acidic the solution. We have tested the blue litmus with multiple pH buffers. The blue paper is blue at pH 8. At pH 7, the sample is maybe just a little red. The real change to red seems to start with pH 6.5 and lower.
  • Red Litmus test paper is a foolproof pH test to determine if something is a base. The Red Litmus test paper does not come with a color chart as it cannot provide you with a defined pH value. The test strip will turn blue if dipped into an alkaline solution (pH >7).
  • Neutral Litmus test paper tests for Neutrality of a solution, or its acidity or alkalinity. The Neutral Litmus test paper does not come with a color chart as it cannot provide you with a defined pH value. The test strip will turn red if dipped into an acidic solution (pH <7) or blue if dipped into an alkaline solution (pH >7).
  • The Congo Red test paper is used to test narrow-range acidic solutions. Congo Red Test Paper is used in acid washes for metal plating where pH values are very low (pH 1.0-3.0). The Congo Red indicator remains blue below pH 3.0, then gradually turns to a brilliant red above pH 5.2.
  • The Universal pH test paper is used to test broad-range solutions from 2.0 to 10.0 in increments of 2.0.

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