A is right, as far as you went, but probably will be counted wrong on an exam BECAUSE you have 4 significant figures in that 3.067 and only 2 in the answer. You need to read and transcribe ALL of those numbers in your calculator (up to 4 of course). I usually carry everything an extra place and round to the right number of s.f. as the last step.
The B part I obtained a slightly different number of 0.01077. I suspect the difference is because you didn't carry either calculation far enough.
For C, of Cu from A divided by 0.250(250 mL converted to L)
This is a longer assignment. I want you to confirm my first two answers and help me figure out the last.
3 Cu (s) + 8 HNO3 (aq) → 3 Cu(NO3)2 (aq) + 2 NO (g) + 4 H2O (l)
A copper penny with a mass of 3.067 g is dissolved in 100.0 ml of 1.000 M nitric acid.
A. How many moles of copper are in the penny, assuming it is pure copper?
0.048 mol Cu
B. When the reaction stops, the undissolved penny is removed. What is the mass of the undissolved penny?
0.0105moles Cu left over or 0.667gCu left over
C. The solution prepared in step B is transferred quantitatively to a 250.00 ml volumetric and diluted to the line. What is the molarity of the Cu2+ ion in this solution?
5 answers
I don't understand. You said to divided answer A by 0.25 but in part b we removed the access copper.
Mols Cu dissolved in A is amount Cu in solution from the dissolution. That is the 0.048 figure. Step B simply removes the SOLID copper (excess Cu) that did not dissolve. You're left with the same solution from step A. So whether you take the solution from step A or the solution from step B the mols DISSOLVED Cu is the same. So if it makes you feel any better use the mols Cu in the solution after step B BUT you must go back to step A to find how much that is since the excess (solid undissolved) Cu doesn't change how much you have in solution. Does this clear it up? If not don't hesitate to say so.
I had a question for C. I did not understand what you put. Do we just divide the 0.048 by 0.250....
nevermind we take the 0.0375 and divide that by the 0.250
2 answers