Calculate the mass of the acid obtained by reacting 37.5 g of a 40% formaldehyde solution with 120 g of copper hydroxide 2.

1) Let’s write the reaction equation and arrange the coefficients:
CH2O + Cu (OH) 2 = HCOOH + CuO + 2H2O
2) Find the mass of the dissolved substance (formaldehyde)
= 40% * 37.5g / 100% = 15g
3) Find the amount of substances (formaldehyde) (M = 30 g / mol)
n = 15/30 = 0.5 mol
4) Find the amount of substances (copper hydroxide 2) (M = 98 g / mol)
n = 120/98 = 1.22 mol – in excess, because 1.22 is more than 1 (we look at the coefficient)
5) Amount of formic acid = amount of formaldehyde = 0.5 mol
6) Mass of acid: m = M * n = 0.5 mol * 46 g / mol = 23 g (M = 46 g / mol)
Answer: 23 g.