What color will the indicator be in a solution of sodium hydroxide?

Question

We know that the indicator phenol red has a pH range of 6.6 to 8.0 over which it undergoes a color change from yellow to red. The options are:

 

1. Red

 

2. Yellow

 

3. Orange

 

4. Colorless 

 

5. The color depends on the concentration of the sodium hydroxide

Answer 1

It will be red.  Bases have pHs > 7.  NaOH is a strong base, so even a dilute solute of it will have a high pH.  But, technically, the color also depends on the concentration of the NaOH.  If extremely dilute, then you could get a pH below 8.  You must have  1 X 10^-6 molar NaOH to get a pH of 8.