Identifying Solution A based on Color Change

Which of the following correctly identifies Solution A?

A. 3.2 x 10^4 mol/L HCl

B. 3.2 x 10^-4 mol/L NaOH

C. 6.3 x 10^-4 mol/L HCl

D. 6.3 x 10^-5 mol/L NaOH

Answer: D. 6.3 x 10^-5 mol/L NaOH

To identify Solution A correctly, we need to consider the color changes it undergoes when alizarin yellow and thymol blue indicators are added. Alizarin yellow changes to yellow when the pH is less than 10.1, while thymol blue changes to blue when the pH is greater than 9. This indicates that the pH of Solution A falls between 9 and 10.1.

Now, let's analyze the given options:

  • A. 3.2 x 10^4 mol/L HCl: pH is not in the range of 9 - 10.1
  • B. 3.2 x 10^-4 mol/L NaOH: pH is 10.5, not in the range of 9 - 10.1
  • C. 6.3 x 10^-4 mol/L HCl: pH is not in the range of 9 - 10.1
  • D. 6.3 x 10^-5 mol/L NaOH: pH is 9.8, falls within the range of 9 - 10.1

Therefore, the correct identification of Solution A is 6.3 x 10^-5 mol/L NaOH.

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