help with moles in solutions please?

Question

what mass of copper(II) oxide would be required to react with 20 cm3 of 2 M hydrochloric acid?

Answer 1

1 dm3 1M HCl contains 1 mol,
1 cm3 1M HCl contains 1*10^-3 mol,
20 cm3 1M HCl contains 2*10^-2 mol,
20 cm3 2M HCl contains 4*10^-2 mol.
The molar mass of Cu(II)O is 79.545 g/mol,
79.545 * (4*10^-2) = 3.1818 g required mass Cu(II)O /answer.