[777888]

1.According to the table of acid-base indicators, what is the colour of METHYL ORANGE in a solution with a pH of 3.9?

2.Separate samples of an unknown solution turned both methyl orange and bromothymol blue to yellow, and turned bromocresol green to blue. Estimate the pH of the unknown solution.


Table of Acid-Base indicators:
Name          Colour of HIn  pH range  Colour of In-
methyl orange      red          3.1-4.4    yellow
methyl red           red          4.4-6.2     yellow
alizarin yellow       yellow     10.0-12.0   violet
bromocresol green  yellow    4.0-5.6      blue
bromothymol blue   yellow    6.2-7.6      blue

[777888]

For question 1, the answer is YELLOW. But I thought that the answer must not be yellow since pH range is 3.1-4.4 (So 3.9 means netural, the colour should be red+yellow=ORANGE, right?)

For question 2, the answer is 5.0. I really don't know why!?
My work:
Turned methyl orange orange to yellow =>pH>4.4
Turned bromothymol blue to yellow =>pH<6.2
Turned bromocresol green to blue =>pH>5.6
Therefore, the pH of the solution must fall bewteen 5.6 and 6.2. I estimate the solution's pH=5.9 (How come the answer is 5.0?)

I don't understand. The answers are from my teacher! I don't know what is happening...my answers are all different. Please help me! Thank you very very much!

[777888]

Does anyone know how to do?

[Tiger]

So obvious right there. Read the column pH range. Just get the pH in the question and put it in the range where it belongs.