Here's how to calculate the mass of 6.25 mol of copper(II) nitrate:

1. Determine the molar mass of copper(II) nitrate (Cu(NO₃)₂):

* Cu: 1 atom * 63.55 g/mol = 63.55 g/mol

* N: 2 atoms * 14.01 g/mol = 28.02 g/mol

* O: 6 atoms * 16.00 g/mol = 96.00 g/mol

Total molar mass = 63.55 + 28.02 + 96.00 = 187.57 g/mol

2. Use the formula:

* Mass = moles * molar mass

3. Calculate the mass:

* Mass = 6.25 mol * 187.57 g/mol

* Mass = 1172.31 g

Therefore, the mass of 6.25 mol of copper(II) nitrate is 1172.31 grams.