calculating molarity?

Question

A 0.1025-g sample of copper metal is dissolved in 35 mL of concentrated HNO3 to form Cu 2+ ions and then water is added to make a total volume of 200 mL. Calculate the molarity of Cu 2+

Answer 1

0.1025 g of Cu is:

n = m/Ar = 0.1025/63.5 = 1.6*10^(-3) mol of Cu, where Ar = 63.5 is the atomic mass of Cu.

According to the chem equation:

Cu + 4HNO3 --> Cu(NO3)2 + 2NO2 + 2H2O

1 mol of Cu gives 1 mol of Cu(NO3)2 or 1 mol of Cu2+ cations. So, we have 1.6*10^(-3) moles of Cu2+ in the final solution, with a molarity of:

[Cu2+] = n/V = 1.6*10^(-3)/ 0.2 = 8.1*120^(-3)

Answer 2

I think this site will help you out

http://dl.clackamas.edu/ch105-04/calculat.htm