To calculate the mass in grams of 5.90 mole of C8H18, we need to use the molar mass of C8H18. The molar mass is the sum of the atomic masses of all the atoms in the molecule.

The atomic mass of carbon (C) is 12.01 g/mol, and the atomic mass of hydrogen (H) is 1.008 g/mol. So, the molar mass of C8H18 is:

(8 x 12.01 g/mol) + (18 x 1.008 g/mol) = 114.23 g/mol

Now, we can calculate the mass of 5.90 mole of C8H18 by multiplying the number of moles by the molar mass:

5.90 mole C8H18 x 114.23 g/mol = 674.087 g

Therefore, the mass of 5.90 mole of C8H18 is 674.087 grams.