An Examination of the Color of Bromthymol Blue Solutions

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An Examination of the Color of Bromthymol Blue Solutions
Bromthymol blue solutions were prepared by diluting 10 mL of 0.16 mM bromthymol blue stock solution to 100 mL with the applicable solvent. 6M sodium chloride solutions were made by adding of 30 g of sodium chloride to the stock solution before diluting. All of the salt dissolved except for solution 9, where it appeared that only half the salt dissolved.
The results of the data are summarized in this table:

Sol'n. Solvent Color* Spectral Maxima

1 0.02M NaOH saturated blue   390 nm, 0.13A; 635 nm, 0.61A

2 pH 7 buffer forrest green   415 nm, 0.19A; 635 nm, 0.28A

3 0.1M HCl bright yellow   435 nm, 0.28A

4 6M HCl bright pink   420 nm, 0.17A; 560 nm, 0.28A

5 6M NaOH blue   390 nm, 0.13A; 620 nm, 0.59A

6 12M NaOH muddy blue   390 nm, 0.13A; 580 nm, 0.38A

7 0.1M HCl + 6M NaCl yellow   440 nm, 0.20A; 575 nm, 0.04A

8 6M H₂SO₄ pink   430 nm, 0.09A; 560 nm, 0.10A

9 6M H₂SO₄ + ~3M NaCl pale pink   425 nm, 0.06A; 560 nm, 0.08A

10 6M NaCl yellow green   440 nm, 0.21A

* color swatches are made by sampling color-corrected photographs of the solutions.
And the data are given here:

Sol'n.	Solvent	Color*	Spectral Maxima
1	0.02M NaOH	saturated blue	390 nm, 0.13A; 635 nm, 0.61A
2	pH 7 buffer	forrest green	415 nm, 0.19A; 635 nm, 0.28A
3	0.1M HCl	bright yellow	435 nm, 0.28A
4	6M HCl	bright pink	420 nm, 0.17A; 560 nm, 0.28A
5	6M NaOH	blue	390 nm, 0.13A; 620 nm, 0.59A
6	12M NaOH	muddy blue	390 nm, 0.13A; 580 nm, 0.38A
7	0.1M HCl + 6M NaCl	yellow	440 nm, 0.20A; 575 nm, 0.04A
8	6M H₂SO₄	pink	430 nm, 0.09A; 560 nm, 0.10A
9	6M H₂SO₄ + ~3M NaCl	pale pink	425 nm, 0.06A; 560 nm, 0.08A
10	6M NaCl	yellow green	440 nm, 0.21A