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Topic: Can someone tell me how this tritration is done ?  (Read 6447 times)

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Offline shalikadm

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Can someone tell me how this tritration is done ?
« on: November 24, 2013, 11:06:39 AM »
I found this titration from a college assignment. I can't understand what are the steps involving this one....I have only done high school titration questions...and do not have practical knowledge.
It's as follows

You have been set the task to investigate a clear lemonade drink. You will be provided with some data

The first set of data is for titrating sodium hydroxide against 25ml of exactly 0.1M HCl

Sample number                          1                   2                    3                       4
NaOH Starting volume cm3       0.00              1.20                0.30                   24.95
End volume cm3                     25.80             28.95              25.90                  50.55
Titre cm3 NaOH

A titration was completed for the lemonade against sodium hydroxide and the values obtained below were for an aliquot of 25ml of the lemonade the results were as follows for a titration against sodium hydroxide

Sample number                           1              2                 3                 4
NaOH Starting volume cm3         0.00         1.20            0.60             12.75
End volume cm3                       12.70        13.40          12.77            24.90
Titre cm3 NaOH


I guess it's happening like this ,
      1.finding the concentration of NaOH using HCl
      2.then using that exactly known concentration of NaOH, find the concentration of the acid in
         lemonade
Is that correct ?

my questions are as follows..
 1. what's in the burette and what’s in the flask ?
 2. what does it mean by starting volume and end volume of NaoH ?
   I guess NaOH is in the flask...please some one point out this to me..

Offline Borek

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Re: Can someone tell me how this tritration is done ?
« Reply #1 on: November 24, 2013, 11:19:02 AM »
1. what's in the burette and what’s in the flask ?

Does it matter? What matters are volumes of both reactants.

Quote
2. what does it mean by starting volume and end volume of NaoH ?

When you fill the burette to exactly zero, volume of the titrant used is just the final reading on the burette. But you can start titrating from any volume - then the volume used is the difference between the final reading and the initial reading.
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Offline shalikadm

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Re: Can someone tell me how this tritration is done ?
« Reply #2 on: November 24, 2013, 11:40:30 AM »
thanks a lot sir for replying...
When you fill the burette to exactly zero, volume of the titrant used is just the final reading on the burette. But you can start titrating from any volume - then the volume used is the difference between the final reading and the initial reading.

Let's take the first set of data..Here's what I think...
Here we have NaOH in the burette and HCL in flask...correct ?
And in the first titration , used volume of NaOH is 25.80ml .in the second one 27.75ml , in the 3rd one 25.60 and in the last one...25.60ml....correct ?
The data shown ,suggest that this burette can hold some thing like 60ml....is it correct ?
In both experiments, I see that the last sample titration is quite different than those done earlier...starting from 24.95 and 12.75...why is that ? and I don't find connection between the starting volumes in each sets...can this be a real investigation...?
I mean the the starting volume must have some connection to the end volume of the titration done before....

thanks

Offline Borek

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Re: Can someone tell me how this tritration is done ?
« Reply #3 on: November 24, 2013, 11:45:55 AM »
Let's take the first set of data..Here's what I think...
Here we have NaOH in the burette and HCL in flask...correct ?

Looks like.

Quote
And in the first titration , use volume of NaOH is 25.80ml .in the second one 27.75ml , in the 3rd one 25.60 and in the last one...25.60ml....correct ?

Yes.

Quote
The data shown ,suggest that this burette can hold some thing like 60ml....is it correct ?

Or 100 mL. Does it matter?

Quote
In both experiments, I see that the last sample titration is quite different than those done earlier...starting from 24.95 and 12.75...why is that ? and I don't find connection between the starting volumes in each sets...can this be a real investigation...?
I mean the the starting volume must have some connection to the end volume of the titration done before....

You are right - but does it matter? Question is not about the reality, but about the result. I agree these data look slightly strange, but I would not care much about it. You can always assume there were not enough titrant to fill the burette back up, so what was added was just the few final drops.
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Offline Hunter2

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Re: Can someone tell me how this tritration is done ?
« Reply #4 on: November 24, 2013, 11:49:35 AM »
Let's take the first set of data..Here's what I think...
Here we have NaOH in the burette and HCL in flask...correct ?

Looks like.

Quote
And in the first titration , use volume of NaOH is 25.80ml .in the second one 27.75ml , in the 3rd one 25.60 and in the last one...25.60ml....correct ?

Yes.

Quote
The data shown ,suggest that this burette can hold some thing like 60ml....is it correct ?

Or 100 mL. Does it matter?

Quote
In both experiments, I see that the last sample titration is quite different than those done earlier...starting from 24.95 and 12.75...why is that ? and I don't find connection between the starting volumes in each sets...can this be a real investigation...?
I mean the the starting volume must have some connection to the end volume of the titration done before....

You are right - but does it matter? Question is not about the reality, but about the result. I agree these data look slightly strange, but I would not care much about it. You can always assume there were not enough titrant to fill the burette back up, so what was added was just the few final drops.

I think for the last titration the guy or girl was to lazy to fill up the burette. As already said it doesnt matter.

Offline shalikadm

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Re: Can someone tell me how this tritration is done ?
« Reply #5 on: November 24, 2013, 11:54:26 AM »
You can always assume there were not enough titrant to fill the burette back up, so what was added was just the few final drops.
I think for the last titration the guy or girl was to lazy to fill up the burette. As already said it doesnt matter.
ya ya. :D :D that may be closest reason...oh I’m getting some insight :)
can you please hold on here...I'm thinking about what to ask next...please don't go offline.. :)

Offline shalikadm

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Re: Can someone tell me how this tritration is done ?
« Reply #6 on: November 24, 2013, 12:04:28 PM »
Yes...the question they ask is....
Using the equation of the reaction for the HCl titration and the calculation from your practical books;  calculate the value exact concentration of the sodium hydroxide used.  Show your calculation
We know the moles of NaOH as we know the moles of HCl...So we have to take the volume from this titration...what is the standard way to get the mean value...?
I remember something like that we ignore first one and take the mean from those last three tests (high school memory) ;)

Offline shalikadm

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Re: Can someone tell me how this tritration is done ?
« Reply #7 on: November 24, 2013, 12:27:56 PM »
Thanks Borek and hunter2...
I took last 3 results ignoring the first test as a rough one...
thanks so much  :-*
« Last Edit: November 24, 2013, 01:34:39 PM by shalikadm »

Offline Borek

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Re: Can someone tell me how this tritration is done ?
« Reply #8 on: November 24, 2013, 03:10:55 PM »
No reason to ignore the result, unless it is substantially different from the other ones.

See for example http://en.wikipedia.org/wiki/Dixon's_Q_test
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Offline shalikadm

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Re: Can someone tell me how this tritration is done ?
« Reply #9 on: November 25, 2013, 12:00:26 AM »
No reason to ignore the result, unless it is substantially different from the other ones.

See for example http://en.wikipedia.org/wiki/Dixon's_Q_test
Me too felt guilty after doing so...here's the results...

Volumes of NaoH used in first set of titrations

for 1st sample = 25.80 - 0.00 = 25.80ml
for 2nd sample = 28.95 - 1.20 = 27.75ml
for 3rd sample = 25.90 - 0.30 =  25.60ml
for 4th sample = 50.55 – 24.95 =25.60ml

Volumes of NaoH used in second set of titrations
for 1st sample = 12.70  - 0.00 = 12.70ml
for 2nd sample = 13.40 - 1.20 = 12.20ml
for 3rd sample = 12.77 - 0.60 =  12.17ml
for 4th sample = 24.90 – 12.75 = 12.15ml
       
So may I ignore the following ?
1st set => for 2nd sample = 28.95 - 1.20 = 27.75ml
2nd test => for 1st sample = 12.70  - 0.00 = 12.70ml
those values have a reasonable gap..
thanks a lot...

Offline Borek

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Re: Can someone tell me how this tritration is done ?
« Reply #10 on: November 25, 2013, 03:50:39 AM »
Why are you so fixed up on ignoring one of the results? Any particular reason to not use them all?

Have you followed the rules of the Dixon's test? Have you calculated gaps and ranges?
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Offline shalikadm

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Re: Can someone tell me how this tritration is done ?
« Reply #11 on: November 26, 2013, 12:23:38 PM »
Have you followed the rules of the Dixon's test? Have you calculated gaps and ranges?
First set of volumes
25.80  27.75  25.60  25.60
25.60  25.60  25.80  27.75
gap = 27.75 - 25.80 = 1.95
range = 27.75 - 25.60 = 2.15
Q95% = 0.829 < Q = 0.906 < Q99% = 0.926

Second set of volumes
12.70  12.20  12.17  12.15
12.15  12.17  12.20  12.70
gap = 12.70 - 12.20 = 0.5
range = 12.70 - 12.15 = 0.55
Q95% = 0.829 < Q = 0.909 <  Q99% = 0.926

Q test is in favour of ignoring those two volumes , at 95% confidence.

Why are you so fixed up on ignoring one of the results? Any particular reason to not use them all?
Here are all the questions that has given in the assignment ...
(1) What causes the lemonade to be acid? (NOTE in steps 2,3 and 4 assume that this is the only acid in the lemonade)
(2) Write a balanced equation  to show the reaction of the acid in the lemonade with sodium hydroxide
(3) Using the equation of the reaction for the HCl titration and the calculation from your practical books;  calculate the value exact concentration of the sodium hydroxide used.  Show your calculation
(4) Using the equation of the reaction found in 2 calculate the number of moles of acid in the lemonade. How many grams of acid would be in a 500ml can of the lemonade? Show your calculations
(5) Draw a flow diagram of the exact practical process you would use to complete the above analysis.
       (flow diagrams will be discussed in the Lectures)
(6) Some methods recommend that the lemonade is boiled first – explain why this might be.
(7) Could you use the same process to analyse the acid in a cola drink. If so what adjustments to the practical work would you have to make. 
(8) Write a balanced equation for the titration of the acid in the cola drink with sodium hydroxide

Calculations seem to be not that much hard. So I think that they except something more than just calculations...I think that they examine whether we are good at the practical side. In practicals , errors can happen and we have to think and make choices to minimize them..I think that they have deliberately put those slightly-away volumes to make us see it and remove it from calculations.
And Also if we take that a drop of NaOH is 0.05 ml, then the guy who has done the first set of titrations has let about 20 more drops to fall and the one who has done the second set of titration has let about 10 more drops to fall accidentally.
It's just what I think about this and have no idea whether it's right.
This assignment was given at School Of Applied Sciences Bournemouth University
I'm eager to see your views..
thanks !

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