Universal indicator

Last updated
A roll of universal indicator paper Universal indicator paper.jpg
A roll of universal indicator paper
Colors of universal indicator Skala boja 2.JPG
Colors of universal indicator

A universal indicator is a pH indicator made of a solution of several compounds that exhibit various smooth colour changes over a wide range pH values to indicate the acidity or alkalinity of solutions. A universal indicator can be in paper form or present in a form of a solution. [1]

Contents

History

Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933. [2] [3] [4]

Composition

A universal indicator is usually composed of water, 1-propanol, phenolphthalein, sodium hydroxide, methyl red, bromothymol blue, sodium bisulfite, and thymol blue. [5] The colours that indicate the pH of a solution, after adding a universal indicator, are:

pH rangeDescriptionColour
≤ 3Strong acidRed
4–6Weak acidOrange or Yellow
7NeutralGreen
8–10Weak alkaliBlue
≥ 11Strong alkaliIndigo or Violet

The colors from yellow to red indicate an acidic solution, colours blue to violet indicate an alkaline solution and a green colour indicates that a solution is neutral.

Universal indicator components [6]
IndicatorLow pH colourTransition pH rangeHigh pH colour
Thymol blue (first transition)Red1.2  2.8Yellow
Methyl orange Red3.2  4.4Yellow
Methyl red Red4.8  6.0Yellow
Bromothymol blue Yellow6.0  7.6Blue
Thymol blue (second transition)Yellow8.0  9.6Blue
Phenolphthalein Colourless8.3  10.0Fuchsia

Wide-range pH test papers with distinct colours for each pH from 1 to 14 are also available. Colour matching charts are supplied with the specific test strips purchased.

Types

Influence on conductivity

Influence of universal indicator solution on the conductivity of desalinated water Universal indicator solution in desalinated water.svg
Influence of universal indicator solution on the conductivity of desalinated water

The impact of an ethanol-based universal indicator may seem negligible at first glance. However, in the case of dilute solutions prepared with bidistilled water, this influence becomes readily discernible and measurable. [7]

See also

References

  1. Walker, Denise (2007). Acids and alkalis (1 ed.). London: Evans. p. 13. ISBN   978-0-237-53002-0 . Retrieved 4 June 2015.
  2. Jap. Pat. 99,664, Feb 21, 1933
  3. Chem Abstr, 28, 2258 (1934)
  4. Foster, L. S.; Gruntfest, I. J. (1937). "Demonstration experiments using universal indicators". Journal of Chemical Education. 14 (6): 274. Bibcode:1937JChEd..14..274F. doi:10.1021/ed014p274.
  5. "Universal Indicator". ISCID Encyclopedia of Science and Philosophy. Archived from the original on September 25, 2006.
  6. Jenkins, Glenn Llewellyn (1979). Jenkins' Quantitative Pharmaceutical Chemistry. Mei Ya. p. 67. Retrieved 4 May 2025.
  7. "Universal_indicator_conductivity/Indicator_conc_conduct.CSV at main · ddiesing/Universal_indicator_conductivity". GitHub .