Stuck on acid/base question from ACER Sample Questions booklet

[swlondon]

Hi guys,

I have brushed up on acid/base reactions and pKa etc.
But for the life of me I cannot begin to understand the answers for Unit 12 in the ACER Sample Questions booklet.

For question 36 they somehow explain that the pH of the sample solution is 9 and that eventually the answer is (D) Green!!!

Is someone able to explain the steps for me please? Are you supposed to use the equations given? Do you need to substitute equations into each other in order to work out the pH.

I can almost taste the answer....for about a year now cos I couldnt get it last year either.

Thank you.

[gbsilp]

the key is in the question where they say about the indicator molecules ratio > 10. A ratio of 10 is 1pH

[goldhawkgonk]

Hello,

There's a full explanation of this problem here:
Paging Dr - Chemistry Q & A
Scroll down to where Elle posts, about 1/2 the way down.

Cheers
edd