Question

Can someone explain this to me?

Answer 1

Other than to say that I see why you are having trouble, I think you could use either.

Having said that, the blue is far more pronounced going from 7 to 9. Seven is more of a dirty blue at 7. It is sky blue at 9. I would pick that.

When you look up it's pH it is given as 7.6 which is about as slightly basic as you can get. At that point it starts to turn blue.

Methyl Red is really weird stuff.

It is red under pH = 4.4 which definitely acidic and yellow above 6.2. It is orange in between.

I would still go with Bromothymol blue, but I'm betting that either could be used.

I hope this is a discussion question, because if you want my honest opinion, it's too close to call.

Answer 2

Answer:

Bromthymol Blue

Step-by-step explanation:

You want to choose an indicator that changes colour at the right pH.

In this case, let's say slightly basic means pH ≈ 8.  

Methyl Red

From the pictures, it looks like pH 6 and pH 8 would have similar colours, and it would be difficult to distinguish them. The solution could be slightly acidic or slightly basic.

Bromthymol Blue

A solution with pH 8 would have a definite blue-green colour, which indicates that the solution is basic with no ambiguity.

I vote for Bromthymol Blue.