Question

A penny having a mass of 2.5340 g was dissolved in 20 mL of 8 M HNO₃. The resulting solution was transferred to a 100.00-ml volumetric flask and diluted to the mark with water. Then, a sample solution was prepared by transferring 10.00 mL of this solution to a 25.00- ml volumetric flask, adding 2.00 mL of 15 M NH₃ and diluting to the mark with water

The concentration of [Cu(NH₃)₄]²⁺ in the sample solution (determined using a Spectro Vis spectrophotometer) is 0.00426 M. 

a) What is the concentration (in M) of  [Cu(NH₃)₄]²⁺ in the original dissolved penny solution? What is the concentration (in M) Cu²⁺ in the original dissolved penny solution? 

b) What is the mass of  Cu²⁺ in the original solution? (Note that this value is also the mass of Cu²⁺ in the penny since the solution contains all of the dissolved penny) 

c) What is the percentage by mass of copper in the penny?

Answer 1

8.

a)

2.5340 g of penny was dissolved in nitric acid and diluted to final volume of 100.00 mL to obtain the original dissolved penny solution.

10.00 mL the above solution was diluted to final volume of 25.00 mL to obtain sample solution.

In the sample solution,

In the original dissolved penny solution,

In the original dissolved penny solution,

b)

Total volume of the original dissolved penny solution is 100.00 mL,

In the original dissolved penny solution, the mass of

c)

Mass of penny is 2.5340 g

The percentage by mass of copper in the penny