Rate of reaction question help

I am really stuck with this question... any help would be great :smile:

Phenolphthalein is a pink colour in alkaline solution. When a solution of phenothylaien in excess sodium hydroxide stands for a few minutes, the pink colour slowly disappears as the pehothylain reacts with the OH- ions.

A solution of phenothylaen of concentration 0.00500 mol dm-3 was mixed with sodium hydroxide of concentration 0.600 mol dm-3. The date in the table shows how the concentration of phenothyleen changed with time.

Time (s)
Phenothyleen (mol dm-3)
0
0.00500
30
0.00385
60
0.00280
90
0.00205
120
0.00150
180
0.00078
240
0.00040
300
0.00020

a)
i) Suggest a method for measuring the concentration of phenothylain in this reaction.
ii) Plot a graph of the concentration of phenothyleen on the vertical axis against time on the horizontal axis.
iii) Use your graph to measure 3 successive half-lives for phenothyleen.
iv) What is the order of the reaction with respect to phenothyleen? Give a reason for your answer.

Reply 1

charco

Study Forum Helper

Original post by laura.cox1

I am really stuck with this question... any help would be great :smile:

Is it just me or does anyone else get the impression that this is someone's homework?

... and what are

pehothylain
phenothyleen
phenothylain
Phenolphthalein
phenothylaien
?

are they all the same or different?

.. and where is the date in the table?
.. is it today?

Reply 2

laura.cox1

Original post by charco

Thankyou for your queries, Charco.
I would like to confirm, that yes, this is my homework, and yes, they are all the same (phenolphthalein).
(My apologies, Charco, the table did not paste correctly when I copied and pasted this question)

Reply 3

250501Ec

Original post by laura.cox1

Charco, the date today is Wednesday 18th April 2018.

Reply 4

charco

Study Forum Helper

Original post by laura.cox1

So, copy-paste changes spelling! hmmmm

TSR is not there to do your homework for you.The idea of homework is to help you learn.

(a) ii, iii, and iv involve plotting graphs and working out half-life (do you know the definition?)

That leaves (a) (i)

Phenoilthaline gives a pink solution with NaOH (given to you in the question). The more there is the more intense the colour is. Do you know of any instrumentation that can detect/measure the intensity of colour in a solution?

Reply 5

laura.cox1

Original post by charco

Hi Mr.Charco
I have already completed all except from aiv (as I am unsure how to classify the graph).
I posted it on the student room because i thought people would help with the topic i am stuck on, not tell me its my homework and then refuse to help

Reply 6

charco

Study Forum Helper

Original post by laura.cox1

https://www.thestudentroom.co.uk/wiki/study_help_guidelines

We are instructed to not give direct answers to questions, rather to guide OPs towards the correct method to solve problems themselves. The link above explains all of this:

Guidance for the OP

"When you do post, post the whole question instead of just a few bits from it; it may not be solvable or may be much harder without some of the details - help us to help you! Also, when posting a question be as specific as possible with what exactly it is you want help, just naming a book/subject area/essay title and asking for help on something that vague isn't likely to get you many, if any, responses and when posting include any progress you already have towards it. What we would not like you to do when posting is to post in a manner that suggests you want other people to do your work for you, which is also likely to lead to you not getting the responses you would like."

Guidance for the study helpers:

"Wherever possible try to guide the asker to the answer rather than just giving the answer straight off! Not much is learned by doing this and the asker may not understand why the answer is what it is.
This Socratic Method of learning - where people ask a question and learn the answer to it by directed prodding and questioning - leads to the best results and understanding.
Not all types of question lends itself to this type of technique but where possible it should be employed and full solutions (especially to calculations) should only be posted as a last resort or a significant misunderstanding has developed. It is at the moderators' discretion to remove, edit or even warn posts that flout this rule, particularly if the post occurs after someone has tried to guide them through the answer."

Reply 7

charco

Study Forum Helper

Original post by laura.cox1

Your original post did not indicate (see what I did there) that you had answered ANY of the question.

You just posted the question, badly.

Why don't you share your answers for the parts that you have completed and explain just where the actual difficulty lies?

Reply 8

laura.cox1

Im sorry, Charco. You are the victim here. IT IS ALL MY FAULT! BLAME ME!
Should i bother taking a photo of my graph, transferring it to different devices in order to attach it to show you when you will just merely, as you put it, 'PRODD' me in the right direction! I do NOT want to be prodded. I want guidance! Not patronising throw off comments from you, sir Charco!

I posted my question on the student room because I wanted other people/students to help me, not to get some 'community helper' (i would describe your job role as something else) tell me off for ever saying a word!
Charco, I would like to conclude my message to you, Sir. Charco, by emphasising to you again my deep condolences for any misconception on my part (which according to you is ALL MY FAULT).