I can't find the answer of A 0.1052 g sample of copper metal is dissolved in 55 mL of concentrated HNO3 to form Cu2+ ions and then water is added to make a total volume of 208.5 mL. (Calculate the molarity of Cu2+.)
I calculated 0.1052*63.546/6.022e23/0.2085 but webassign told me its wrong
You have
0.1052/63.546 = .0016555 moles Cu
.0016555mole/.2085L = .00794 M
Don't know why you tossed in Avogadro's number - who cares how many ions there are? Molarity is moles/liter. And, it makes no difference how the ions were produced. You are only interested in moles of Cu2+/liters of solution
I think
Steve thinks right. The 6.02E23 is extraneous to the problem.
To calculate the molarity (M) of Cu2+, you need to first determine the number of moles of Cu2+ ions in the solution.
To do this, you can use the given mass of copper metal (0.1052 g) and the molar mass of copper (63.546 g/mol) to find the number of moles of copper metal:
moles of Cu = mass of Cu / molar mass of Cu
= 0.1052 g / 63.546 g/mol
= 0.001654 mol
Since the balanced chemical equation shows that 1 mole of copper metal (Cu) forms 1 mole of copper ions (Cu2+), we can assume that the number of moles of Cu2+ ions is also 0.001654 mol.
Now, you need to calculate the volume of the solution in liters (L):
volume of solution = volume of HNO3 + volume of water
= 55 mL + (208.5 mL - 55 mL) [substituting the given volumes]
= 208.5 mL [simplifying]
= 0.2085 L [converting to liters]
Finally, you can calculate the molarity (M) of Cu2+ by dividing the number of moles of Cu2+ ions by the volume of the solution in liters:
Molarity of Cu2+ = moles of Cu2+ / volume of solution
= 0.001654 mol / 0.2085 L
≈ 0.007937 M
Therefore, the molarity of Cu2+ in the solution is approximately 0.007937 M.