Solving Rate of Reaction Problems: Ethyl Ethanoate and Sodium Hydroxide

[jsmith613]

Homework Statement

http://www.mrev.org.uk/A-Level_Site/New%20A-Level%20Unit%204/Rates.html
(the answers are at the top - see link)

Could someone please help me with the question (about half way through) on ethyl ethanoate and sodium hydroxide.
in cii) we identified the half life doubles
ciii) we identified the order is second order

for part civ) we are asked is this the order for OH- ions or total order.
I would have said OH- order BUT the answer is total order.
Please could someone explain this (the mark schemes explanation is ester and NaOH are equimolar at the start - how is this relevant)

thanks

Homework Equations

NONE

The Attempt at a Solution

I have shown my attempts above in the body of this question

 

[jsmith613]

questions like this come up often and I am worried it may come up in mine so i would really like to understand the theory behind it

 

[jsmith613]

i read a few books and they all agree the graph should only show order with respect to OH ions
why is this not the case here

 

[nobahar]

It might be better if you present the relevant information here. I couldn't find what you're talking about!