Brønsted Acid-Base Reactions
Tayah Walker
Suzanne Sene
Justin Duncan
Etan Seebaluck
CHEM 1252L-045
11/14/19
Abstract:
In this lab, the pH range of various solutions were measured using acid-base indicators.
With this information, the solutions were then ranked in order of increasing pH. Since the
relationship between pH and Kₐ is inverse, as the pH of these solutions increased, their Kₐ values
decreased. According to the Brønsted Acid-Base Theory, the larger the Kₐ value, the stronger the
acid (Bronsted). A collection of Brønsted acids, Brønsted bases, and amphiprotic substances
were tested, eight solutions in total. These eight solutions were tested with the following five
indicators, bromothymol blue, bromocresol green, thymol blue, phenolphthalein, and alizarin. A
few drops of each solution were dropped into 5 separate microwells out of a microwell strip. One
of each indicator was dropped into the microwell where a color change was observed and
recorded. Applying the colors observed to a colorimetric comparison chart allowed for the
detection of each substance’s pH range. Acetic acid was discovered to have a pH range of 1.2-
2.8. Ammonium was discovered to have a pH range of 5.5-6.0; Acetate, 7.6-8.0; Carbonate, 10-
12; Sulfate, 5.4-6.0; Bicarbonate, 10-12; Ammonium Hydroxide was concluded to have a range
of 10-12. Lastly, Sulfate was determined to have a pH of less than 1.2. The result of this lab was
the ranking of the Brønsted acids by their Ka values and the Brønsted bases by their Kb values.
The Brønsted acid ranking in decreasing order of strength was acetic acid then ammonium, with
Ka values 0.0290-1.29 × 10'( and 5.1 × 10'**-5.0 × 10'*+ respectively. The