posted by nick .
assuming you have o.4g of Y(OH)3, calculate the mass of BaO2 required to react stoichiometrically to produce YBa2Cu3O7. Now calculate the mass of CuO.
Write the balanced equation. Then, calculate the moles of Y hydroxide from .4 g. Then, notice from the balanced equation how many moles of Barium oxide will be required, and convert that to grams.