[ganesh2gig]

hi everybody

i am doing a iodometric titration of copper sulfate as specified by the USP .

Place about 650 mg of Cupric Sulfate in an accurately weighed container fitted with a ground-glass stopper, dry, allow to cool in a desiccator, and weigh again to obtain the weight of the specimen. Dissolve in 50 mL of water, add 4 mL of 6 N acetic acid and 3 g of potassium iodide, and titrate the liberated iodine with 0.1 N sodium thiosulfate VS, adding about 2 g of potassium thiocyanate and 3 mL of starch TS as the endpoint is approached. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N sodium thiosulfate is equivalent to 15.96 mg of CuSO4.


when i use this conversion factor , i am supposed to get the percentage purity of the
copper sulfate .

assuming the titration consumes 6 ml , i would get 99% purity .

form this how do i calculate the percentage of copper in it ?

[ganesh2gig]

can somebody please give the example of calculation .

[Borek]

Place about 650 mg of Cupric Sulfate

Cupric?

Each mL of 0.1 N sodium thiosulfate is equivalent to 15.96 mg of CuSO4.

What was volume of titrant used?

assuming the titration consumes 6 ml , i would get 99% purity

No, you would get 6*15.96mg of CuSO4. To calculate purity you need to take into account initial sample mass.

[ganesh2gig]

thanks for taking the time to read it

the following method was taken from USP .

my doubt is

first we calculate the theoretical % of copper assume it is for 100%

then by volumetric method we calculate that it is nearly 98-99 %.

by cross multiplication we can get the copper percentage  .

is this method correct ?

[Borek]

by cross multiplication we can get the copper percentage

Huh? You have copper percentage from titration, why do you want to use cross multiplication to calculate it again?

[ganesh2gig]

how do i calculate the % of copper from copper sulfate ?

from the above method i am only getting the purity of cuso4 in total.

 

[Borek]

Please elaborate. You are so vague your post doesn't make any sense to me.

[saden99]

Are you asking for a way to calculate the copper ions in the sample? If you know the amount of the CuSO4 (or whatever you're trying to determine with copper in it), then you could get the amount of copper easily knowing the two molecular weights.


For arguments sake....


You have 1g of CO2 whose molecular weight is 44.011g/mol so you can find what percentage of that 1 gram is just carbon or just oxygen. In this case....27% and 72% respectively.

I think I said that correctly...I am rather tired.

You are only giving a percentage of purity of CuSO4...so try relating the above method to finding percentage of CuSO4. This is something that is not emphasized much in general chemistry courses so students never fully understand it, but it can be used to calculate a variety of things such as impurities from polymer reactions.

[ganesh2gig]

thanks for the info .