writing net equation etc
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#1
August 18th, 2006, 02:07
 redXI Junior Member Join Date: Aug 2005 Posts: 14
writing net equation etc

The concentration of Cu^2+ ions in the water(which also contains sulfate ions)discharged from certain industrial plant is determined by adding excess sodium sulfide(Na2S) solution to 0.800 L of the water. The molecular equation is; Na2S(aq) + CuSO4 (aq) --> CuS(s) + Na2SO4 (aq)
A. How do I write the ionic equation? (I can do it fine but I'm confused with the state of each... )
B. How do I calculate the molar concentration of Cu^2+ in the water sample if 0.0177 g of solid CuS is formed? Is it true that the answer is 2,31 x 10^-4? My teacher once explained it to me but I wasn't paying attention. Pity me and I must be really bad at chemistry :x

Oh yeah and I just remember that I have this question which I found during my visit to other school, here it is: Physiological saline used in intravenous drips is approximately 0,9 % NaCl solution. 100g of physiological saline solution was treated with excess AgNO3 solution and formed 2,22 of AgCl precipitate. Can you calculate the % mass of NaCl in the physiological saline solution.
As for me, I can do up until the half way only...
#2
August 20th, 2006, 03:15
 sdekivit Member Join Date: Jul 2005 Location: Holland Posts: 27

You add Na2S to water containing Cu(2+)-ions and SO4(2-) ions. The net equation will therefore be:

Na2S + Cu(2+) --> Na(+) + CuS

Now you have the stoichiometry and you have to convert the mass of CuS to mol. Use the stoichiometry to find the amount of Cu(2+) that is needed to form 0,0177 g CuS.

The calculate molarity with c = n/V.

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