.

[andrewloppol]

.

[fady_22]

11. Could it also be because it is not very soluble in water?

[superflya]

11. Could it also be because it is not very soluble in water?

yea i would think so.

[simonhu81292]

11. Could it also be because it is not very soluble in water?

yea i would think so.

iodine dissolves easily in most organic solvents such as hexane or chloroform due to its lack of polarity, but is only slightly soluble in water. However, the solubility of elemental iodine in water can be increased by the addition of potassium iodide.

[physics]

Question 10 : ( my dodgy answer which i am kinda sure is right)
due to inaccurate measurements your answer might by higher ( i know mine was due to shit scales)
insolubles that werent stated or considered because of it only being in trace amounts and
 i agree with the insolubes and contaminate bit



i think so...

[physics]

I wrote for the errors:

Manufacturers specification: 500mg per ~1g tablet ⇒ 50% vitamin C
Experimental result: 366mg per 0.49g tablet ⇒ 74.7% vitamin C
Errors that may account for the difference in results:
Parallax errors ⇒ incorrectly misjudging the readings on the burette or aliquot when measuring amounts. This may increase (in this case) or decrease the titre, altering the final percentage by mass calculations by increasing it or decreasing it respectively. To prevent parallax errors, read measurements at eye level to ensure accuracy to reduce errors.
Misjudging the color of the indicator near the end point ⇒ it is crucial that care is taken when watching for colour change as the mixture reaches the steep and sensitive end point. Failure to record the exact titre when there is a total colour change will increase the titre, incorrectly increasing the final percentage by mass calculations of ascorbic acid in the sample.
Impurities and contaminants ⇒ Other compounds may have been present in any of the pieces of equipment. The burette, flasks, stirring rods and pipette may have not been thoroughly washed after each use, resulting in other compounds entering the solutions being titrated. This may have altered the final calculations depending on what impurities were present. Reagents present from previous use may alter concentrations of the solutions. Iodine present in the flasks may have caused the end point to occur earlier (not in this case). The presence of other impurities may have resulted in a slightly later occurring end point. This slight presence of impurities may have had a significant effect on the titre, especially when the end point is very steep, and will increase the titre and final calculations (in this case) if the impurity caused a later occurring end point.
These are all possile reasons for the discrepancy between the manufacturers specification and the experimental result.

Then for the Iodine one:

Solid iodine is a volatile substance that evaporates readily at normal temperatures and pressures, sublimating into a posionous violet coloured gas. Due to its deterioration, solid iodine cannot be used as a primary standard as the loss of iodine by sublimation would alter the known mass and concentration of the standard solution being made from it, therefore altering the results of the titration. A primary standard needs to be stable and non-volatile, whereas solid iodine is not. Pure solid Iodine is also corrosive and poisonous which can be unsafe for novice chemists.

And doing the dessicant now

u sure right good. A+ for sure...if only i wrote so good for my chem prac. teacher complains that i dont make sensse =.=

[physics]

I wrote for the errors:

Manufacturers specification: 500mg per ~1g tablet ⇒ 50% vitamin C
Experimental result: 366mg per 0.49g tablet ⇒ 74.7% vitamin C
Errors that may account for the difference in results:
Parallax errors ⇒ incorrectly misjudging the readings on the burette or aliquot when measuring amounts. This may increase (in this case) or decrease the titre, altering the final percentage by mass calculations by increasing it or decreasing it respectively. To prevent parallax errors, read measurements at eye level to ensure accuracy to reduce errors.
Misjudging the color of the indicator near the end point ⇒ it is crucial that care is taken when watching for colour change as the mixture reaches the steep and sensitive end point. Failure to record the exact titre when there is a total colour change will increase the titre, incorrectly increasing the final percentage by mass calculations of ascorbic acid in the sample.
Impurities and contaminants ⇒ Other compounds may have been present in any of the pieces of equipment. The burette, flasks, stirring rods and pipette may have not been thoroughly washed after each use, resulting in other compounds entering the solutions being titrated. This may have altered the final calculations depending on what impurities were present. Reagents present from previous use may alter concentrations of the solutions. Iodine present in the flasks may have caused the end point to occur earlier (not in this case). The presence of other impurities may have resulted in a slightly later occurring end point. This slight presence of impurities may have had a significant effect on the titre, especially when the end point is very steep, and will increase the titre and final calculations (in this case) if the impurity caused a later occurring end point.
These are all possile reasons for the discrepancy between the manufacturers specification and the experimental result.

Then for the Iodine one:

Solid iodine is a volatile substance that evaporates readily at normal temperatures and pressures, sublimating into a posionous violet coloured gas. Due to its deterioration, solid iodine cannot be used as a primary standard as the loss of iodine by sublimation would alter the known mass and concentration of the standard solution being made from it, therefore altering the results of the titration. A primary standard needs to be stable and non-volatile, whereas solid iodine is not. Pure solid Iodine is also corrosive and poisonous which can be unsafe for novice chemists.

And doing the dessicant now

u sure right good. A+ for sure...if only i wrote so good for my chem prac. teacher complains that i dont make sensse =.=

ROFL - bio made me write good science things lol..

bio made me feel as though i couldn't right good explanations =.=

[Potter]

Hey guys I'll need to post Q's occasionally, appreciate answers .

 10. Why was your percentage by mass of ascorbic acid (titrated with iodine) higher than the manufacturers? (Teacher says coz I₂ is volatile?.. I said: Parallax errors and Impurities and contaminants?

 11.  Why is solid iodine not considered a good primary standard? Volatile/deteriorates?


 12.  Explain why the dessicating agent helps keep the vitamin C tablets in good condition.

Cheers for answers .

11. Your teacher is pretty much right. If you read the chem prac sheet, giving background on the topic it states it there.
I2 is volatile and changes concentration constantly. Therefore it is hard to get an accurate result.
12.Ascorbic Acid oxidizes when exposed to moisture. Hence it's necessary to have a desiccant to keep the tablets in cond.

 

[Greggler]

lol good ol' days of biol

have to be so comprehensive lol