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1. Determining percentage of copper in sample of brass,
6g of brass was reacted completely with nitric acid.

Resulting solution was neutralised and made up to 500cm^3 in a volumetric flask

excess KI(aq) was added to 25cm^3 of this solution. iodine formed required 18.90cm3 of 0.200moldm3 Na2S2O3 for complete reaction/
a mole of s2o32- is equivalent to one mole of cu2+

determine percentage by mass of copper in sample of brass

n Na2S2O3 = 0.200*(18.90/1000)
=0.00378 so 0.00378 n of Cu2_
in 500cm3, = 0.0756

mass = 0.0756 * 63.5
4.80/6.00 = 80.0%
2. (Original post by ILoveUSA)
Determining percentage of copper in sample of brass,
6g of brass was reacted completely with nitric acid.

Resulting solution was neutralised and made up to 500cm^3 in a volumetric flask

excess KI(aq) was added to 25cm^3 of this solution. iodine formed required 18.90cm3 of 0.200moldm3 Na2S2O3 for complete reaction/
a mole of s2o32- is equivalent to one mole of cu2+

determine percentage by mass of copper in sample of brass

n Na2S2O3 = 0.200*(18.90/1000)
=0.00378 so 0.00378 n of Cu2_
in 500cm3, = 0.0756

mass = 0.0756 * 63.5
4.80/6.00 = 80.0%
I've quickly done the calculation myself, and indeed you do have the correct answer
3. I believe it is

Posted from TSR Mobile
4. (Original post by ZakRob)
I've quickly done the calculation myself, and indeed you do have the correct answer
Woo! Thanks!

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Updated: April 9, 2013
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