Ok guys, this is pissing the hell out of me. I find that questions involving Redox are just plain ****** up. But hold up, before this becomes a whiner post.
Question:
A sample of pentahydrate, Cu2SO4.5H2O was dissolved to form copper (II) sulphate solution. 25.0cm^3 of this solution was added to 30cm^3 of excess potassium iodide solution. The iodine liberated was titrated with 22.50cm^3 of 0.108 mol/dm^3 sodium thiosulphate solution. What was the mass in grams of the pentahdrate, per dm^3 of the solution?
What i meant by ****** up is, there are so many possible mol ratios to compare to one and other, how do i know what to do? Instead of giving me the solutions, can you guys kindly guide me on the thinking process? That way it'll help me understand clearer.
Originally posted by Lord dejavu:Ok guys, this is pissing the hell out of me. I find that questions involving Redox are just plain ****** up. But hold up, before this becomes a whiner post.
Question:
A sample of pentahydrate, Cu2SO4.5H2O was dissolved to form copper (II) sulphate solution. 25.0cm^3 of this solution was added to 30cm^3 of excess potassium iodide solution. The iodine liberated was titrated with 22.50cm^3 of 0.108 mol/dm^3 sodium thiosulphate solution. What was the mass in grams of the pentahdrate, per dm^3 of the solution?
What i meant by ****** up is, there are so many possible mol ratios to compare to one and other, how do i know what to do? Instead of giving me the solutions, can you guys kindly guide me on the thinking process? That way it'll help me understand clearer.
Note : Copper(II) sulfate pentahydrate is *not* Cu2SO4.5H2O, it should be CuSO4.5H2O.
Helps for you :
1) Write the balanced redox between Cu2+ and I-, to generate Cu+ and I2 ---> eqn 1.
2) Write the balanced redox between S2O3 2- and I2, to generate S4O6 2- and I- ---> eqn 2.
3) Based on no. of moles of thiosulfate used, find no. of moles of iodine present (use eqn 2).
4) Based on no. of moles of iodine present, find moles of Cu2+ (use eqn 1).
5) Based on volume of solution, find molarity of CuSO4.
6) State that molarity (ie. no. of moles per dm3) of Cu2+ = no. of moles of copper(II) sulfate pentahydrate added to 1dm3.
7) Based on no. of moles of copper(II) sulfate pentahydrate, find sample mass of copper(II) sulfate pentahydrate added.
Thanks a bunch UltimaOnline. I got stuck at steps 5 and 6.
For step 6, can you explain to me how it works? Why does molarity of Cu2+ = no. of mols of copper sulphate pentahydrate added to 1dm3?
Originally posted by Lord dejavu:Thanks a bunch UltimaOnline. I got stuck at steps 5 and 6.
For step 6, can you explain to me how it works? Why does molarity of Cu2+ = no. of mols of copper sulphate pentahydrate added to 1dm3?
Because 1 mole of CuSO4.5H2O (per dm3 solution) contains 1 mole of CuSO4 (per dm3 solution) which contains 1 mole of Cu2+ (per dm3 solution).