Does the Bromide test in the full text of the Hydrochloric acid Monograph in the ACS Reagent Chemicals require phenol red or phenol red sodium salt as part of the indicator solution?
Quote from the bromide test' phenol red indicator solution (0.020 g of sodium salt in 100 mL of water)' because the mentioned preparation from the Reagents, Buffers and Indicators chapter only says this:
'Phenol Red Indicator II, pH 4.7 (For determination of bromide.) Dissolve 33 mg of phenol red in 1.5 mL of 2 N sodium hydroxide solution and dilute with water to 100 mL (this is solution A). Dissolve 25 mg of ammonium sulfate in 235 mL of water; add 105 mL of 2 N sodium hydroxide solution and 135 mL of 2 N acetic acid (this is solution B). Add 25 mL of solution A to solution B and mix. Using a pH meter, adjust the pH of this solution to 4.7 if necessary.'
I, therefore, would like this clarified if that is possible?
No, the Bromide test in the full text of the Hydrochloric acid Monograph in the ACS Reagent Chemicals does not require phenol red or phenol red sodium salt as part of the indicator solution. The preparation mentioned in the Reagents, Buffers, and Indicators chapter provides ez2 results an alternative indicator solution using phenol red for determining bromide.
Thank you for the reply.
I'm still not certain since the full text in the monograph specifies 'phenol red indicator solution (0.020 g of sodium salt in 100 mL of water)'. My question would be specific to this wording.
Is the phenol red indicator solution to be made up with 0.020g phenol red sodium salt or is any phenol red solution made with only phenol red with this amount of sodium acceptable?
Without reading the full text referenced, I will say that most bromide tests are using bromide as a reagent - not phenol red. Bromide (Br2) is a dark red/brown color. Therefore, you have a colorized test for double bonds, for instance.
With regards to phenol red, the chemical phenol red itself is typically sold as a sodium salt. Sodium is just the counter ion to the negative phenol red molecule. Therefore, the instructions listed are for making a solution of phenol red indicator, starting with a solid phenol red sodium salt. Many chemicals come as a salt of some sort so no, that much sodium ion shouldn't hurt your reaction unless it was particularly sensitive to sodium.
Hope that helps!
The preparation mentioned in the Bromide test for the phenol red indicator solution states: "phenol red indicator solution (0.020 g of sodium salt in 100 mL of water)." This indicates that the phenol red used in this context is indeed the sodium salt form of phenol red, not the free acid form. The separate preparation you mentioned, referred to as "Phenol Red Indicator II, pH 4.7," involves dissolving phenol red in a sodium hydroxide solution nia vardalos to form solution A, which is then mixed with solution B containing sodium hydroxide and acetic acid.