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Offline Hemidol

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Moles problem
« on: November 17, 2009, 10:31:40 PM »
From the volume of titrant added, calculate the moles of vitamin C for each titration. Show a sample
calculation for trial 1. From the results this, calculate the average value for the number of moles of vitamin C titrated. Report the final value to the appropriate number of significant figures.


Given these values:
concentration of KIO3 M:  0.002034
weight of tablet: 0.3g

trial #1:
final buret reading: 20mL
initial buret reading: 30mL
volume of KIO3: 10mL
weight of vitamin C tablet: 5g

trial #2:
final buret reading: 12mL
initial buret reading: 20mL
volume of KIO3: 8mL

The key reaction of this experiment was :
IO3- + 5I- + 6 H+ -> 3 I2 + 3 H2O

how can I do this?? This was an experiment involving identifying the compositon of vitamin C
« Last Edit: November 17, 2009, 11:19:36 PM by Hemidol »

Offline Hemidol

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Re: Moles problem
« Reply #1 on: November 18, 2009, 12:33:19 AM »
Don't mean to double post but I can't edit my message... I have some further questions that I'm interested in answering here.

From the results of question 1, calculate the average value for the number of moles of vitamin C titrated.
Report the final value to the appropriate number of significant figures.


-- To answer this I would just take the mole value above (for trial 1); do the same thing for trial do, add them together and divide by 2--correct?

3. Calculate the % error of the mole values used to calculate the average in question 2.

Not sure how I do this.

Using the average moles of vitamin C titrated, calculate the amount of vitamin C, in mg, that was in the
tablet you analyzed. (Hint: Remember how the tablet was prepared and put into solution before titration).


I believe for this I can write:

Avg moles vitamin C * XXXX grams vitamin C / 1 mole vitamin C * 1000mg/1g * 20 (this is a value given to us)

is that correct technique?

Calculate the % composition of vitamin C in the tablet.

Not sure how to do this..

Offline Borek

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Re: Moles problem
« Reply #2 on: November 18, 2009, 03:04:08 AM »
The key reaction of this experiment was :
IO3- + 5I- + 6 H+ -> 3 I2 + 3 H2O

This is one of two key reactions. The other one is the direct reaction between iodine and ascorbic acid.

ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Hemidol

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Re: Moles problem
« Reply #3 on: November 18, 2009, 12:48:18 PM »
Yup your 100% right. For the very firstquestion, I believe I can write:

10ml * 0.002034M KIO3 * 3 mole KIO3 (from mole-mole ratio) = XXXX mole vit C


correct releshonship?
« Last Edit: November 18, 2009, 01:29:15 PM by Hemidol »

Offline jsmith613

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Re: Moles problem
« Reply #4 on: November 18, 2009, 01:19:04 PM »
From the volume of titrant added, calculate the moles of vitamin C for each titration. Show a sample
calculation for trial 1. From the results this, calculate the average value for the number of moles of vitamin C titrated. Report the final value to the appropriate number of significant figures.


Given these values:
concentration of KIO3 M:  0.002034
weight of tablet: 0.3g

trial #1:
final buret reading: 20mL
initial buret reading: 30mL
volume of KIO3: 10mL
weight of vitamin C tablet: 5g

trial #2:
final buret reading: 12mL
initial buret reading: 20mL
volume of KIO3: 8mL

The key reaction of this experiment was :
IO3- + 5I- + 6 H+ -> 3 I2 + 3 H2O

how can I do this?? This was an experiment involving identifying the compositon of vitamin C


personally i would use the formula
moles = mass / RFM

moles = 0.3 / 176 (RFM of C6H8O6

moles = 0.0017045454545

Offline Hemidol

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Re: Moles problem
« Reply #5 on: November 18, 2009, 01:30:55 PM »
From the volume of titrant added, calculate the moles of vitamin C for each titration. Show a sample
calculation for trial 1. From the results this, calculate the average value for the number of moles of vitamin C titrated. Report the final value to the appropriate number of significant figures.


Given these values:
concentration of KIO3 M:  0.002034
weight of tablet: 0.3g

trial #1:
final buret reading: 20mL
initial buret reading: 30mL
volume of KIO3: 10mL
weight of vitamin C tablet: 5g

trial #2:
final buret reading: 12mL
initial buret reading: 20mL
volume of KIO3: 8mL

The key reaction of this experiment was :
IO3- + 5I- + 6 H+ -> 3 I2 + 3 H2O

how can I do this?? This was an experiment involving identifying the compositon of vitamin C


personally i would use the formula
moles = mass / RFM

moles = 0.3 / 176 (RFM of C6H8O6

moles = 0.0017045454545

But its requesting to find it from the volume of titrant added.. so you can't do it that way.

Offline jsmith613

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Re: Moles problem
« Reply #6 on: November 18, 2009, 01:55:58 PM »
Quote

But its requesting to find it from the volume of titrant added.. so you can't do it that way.

If we knew the vol of KIO3 used it would be easier, we already know its concentration as you said before (0.002034) therefore if we knew the vol of KIO3 used we could work out the volume. What volume of KIO3 was used?

Offline Hemidol

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Re: Moles problem
« Reply #7 on: November 18, 2009, 02:02:14 PM »
Quote

But its requesting to find it from the volume of titrant added.. so you can't do it that way.

If we knew the vol of KIO3 used it would be easier, we already know its concentration as you said before (0.002034) therefore if we knew the vol of KIO3 used we could work out the volume. What volume of KIO3 was used?
lol its right there, 8ml and 10ml (in their respective trials)

Offline jsmith613

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Re: Moles problem
« Reply #8 on: November 18, 2009, 04:54:30 PM »
So moles = concentration * vol dm3
10 ml = 0.01 dm3

moles in KIO3 = 0.002034 * 0.01
moles = 0.00002034

(seems strange so i think someone should check it)
then if 1 mole of KIO3 reacts with 1 mole of vitamin C, moles of vitamin C = 0.00002034
if 1 mole of KIO3 reactions with 2 mole then 0.00002034 * 2
etc...

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