Here's how to calculate the mass of 4.55 moles of CH2O (formaldehyde):

1. Find the molar mass of CH2O:

* Carbon (C): 12.01 g/mol

* Hydrogen (H): 1.01 g/mol (x 2 = 2.02 g/mol)

* Oxygen (O): 16.00 g/mol

* Total molar mass: 12.01 + 2.02 + 16.00 = 30.03 g/mol

2. Use the formula: mass = moles x molar mass

* mass = 4.55 moles * 30.03 g/mol

* mass = 136.64 g

Therefore, the mass of 4.55 moles of CH2O is approximately 136.64 grams.