number 8 7. During the preparation of the brass solution suppose a trace of some
ID: 714961 • Letter: N
Question
number 8
7. During the preparation of the brass solution suppose a trace of some other metal ion that absorbs at 620 mu enters the solution. Would this cause the percent copper found to be higher, lower, or equal to the true percentage of cop per in the brass sample? Higher 8. Suppose that a student performed the experiment and calculations perfectly except for the following. Unknown to the student, Cu(NO3)2 3H20 instead of CusO4 5H20 was used to make up the known Cu+2 solution. Using his data the student found a percentage of copper in the brass samples of 50.0%. would this percentage be correct? If so, why? If not, what is the correct percentage? Show how you got your answer.Explanation / Answer
The salt that should be used by the student is CuSO4.5H2O
The percentage of Cu2+ in the above copper(II) salt = (63.546/249.677)*100 = 25.45 %
The salt that was used by the student is Cu(NO3)2.3H2O
The percentage of Cu2+ in the above copper(II) salt = (63.546/241.599)*100 = 26.30 %
The difference in the percentage of Cu2+ = 25.45 - 26.30 = -0.85 %
For 25.45 %, the error is -0.85 %
Now, for 50%, the error is (50/25.45)*-0.85 = -1.67 %
Hence, the percentage of copper in the brass sample is not accurate, with an error of -1.67 %.
Hence, the correct percentage of copper = 51.67 %
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