Final answer:
To obtain 0.78 mol of C8H18, one would need to measure out 89.09 grams of it, using the molar mass of C8H18 which is 114.23 g/mol.
Step-by-step explanation:
The question asks us to calculate how many grams of C8H18 (octane) would be needed to have 0.78 mol of the substance. To find this, we need to know the molar mass of C8H18, which is the sum of the molar masses of carbon (C) and hydrogen (H) in the molecule. The molar mass of C is approximately 12.01 g/mol, and the molar mass of H is approximately 1.008 g/mol. Therefore, the molar mass of C8H18 is calculated as (8 moles of C)(12.01 g/mol) + (18 moles of H)(1.008 g/mol) = 114.23 g/mol.
Next, we multiply the molar mass of C8H18 by the number of moles we have:
0.78 mol C8H18 × 114.23 g/mol = 89.09 g of C8H18