Question on Finding Rate of Reaction by Titration

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Alpha-Omega
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#1
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#1
Here's the method:

1. Measure out sample of reactants with known concentration.
2. Mix them together, start a clock and stir the mixture thoroughly.
3. At regular time intervals, withdraw samples using a pipette and quench (stop/slow down)
the reaction. The time at which half the contents of the pipette have been added
to the quenching solution is noted.
4. The quenched solution is then titrated against a suitable titrant.

On Step 3, why only half? Why not all of the contents in the pipette?
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nmudz_009
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#2
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#2
(Original post by Alpha-Omega)
Here's the method:

1. Measure out sample of reactants with known concentration.
2. Mix them together, start a clock and stir the mixture thoroughly.
3. At regular time intervals, withdraw samples using a pipette and quench (stop/slow down)
the reaction. The time at which half the contents of the pipette have been added
to the quenching solution is noted.
4. The quenched solution is then titrated against a suitable titrant.

On Step 3, why only half? Why not all of the contents in the pipette?
This unit 5 chemistry isn't it? Did it before christmas but I completely forgot tho but it's part of the method so there's a simple reason check your notes
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Alpha-Omega
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#3
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#3
(Original post by nmudz_009)
This unit 5 chemistry isn't it? Did it before christmas but I completely forgot tho but it's part of the method so there's a simple reason check your notes
I don't have any notes for it as I had been doing the AS modules since Sept. I just started
today on A2 (Unit 4 on Edexcel).

There is only one page about this topic in the textbook I'm using and only one line
in the CGP revision guide and it doesn't mention the reason why only half is used.
I doubt this would be asked in the exam, but I want to understand the whole process, because it makes remembering it easier.
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charco
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#4
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#4
(Original post by Alpha-Omega)
Here's the method:

1. Measure out sample of reactants with known concentration.
2. Mix them together, start a clock and stir the mixture thoroughly.
3. At regular time intervals, withdraw samples using a pipette and quench (stop/slow down) the reaction.

The time at which half the contents of the pipette have been added to the quenching solution is noted.
4. The quenched solution is then titrated against a suitable titrant.

On Step 3, why only half? Why not all of the contents in the pipette?
The moment the first drop arrives from the pipette it starts quenching. But the stuff still in the pipette doesn't.
The half time is taken as the average between the start time and the time it's all added.
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Alpha-Omega
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#5
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#5
(Original post by charco)
The moment the first drop arrives from the pipette it starts quenching. But the stuff still in the pipette doesn't.
The half time is taken as the average between the start time and the time it's all added.
That makes sense.

This unit 5 chemistry isn't it? Did it before christmas but I completely forgot tho but it's part of the method so there's a simple reason check your notes
You're right, it actually has a simple reason.

(Original post by charco)
.
Off-topic question, but is a colorimeter a type of spectrophotometer?
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charco
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#6
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#6
(Original post by Alpha-Omega)
That makes sense.



You're right, it actually has a simple reason.



Off-topic question, but is a colorimeter a type of spectrophotometer?
Yes, a colorimeter is a spectrometer that only operates in the visible region of the spectrum and generally uses colour bands by means of filters, rather than specific wavelengths.
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Ellie.Ginger
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#7
Report 3 years ago
#7
Isn't the time same for all the samples taken from the solution mixture?
(Original post by charco)
The moment the first drop arrives from the pipette it starts quenching. But the stuff still in the pipette doesn't.
The half time is taken as the average between the start time and the time it's all added.
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