When 34.5 g of the higher oxide of a group V element were dissolved in water, 42.6 g of a tribasic acid were formed.

When 34.5 g of the higher oxide of a group V element were dissolved in water, 42.6 g of a tribasic acid were formed. Set the oxide formula.

m (H2O) = 42.6 – 34.5 = 8.1 g
X2O5 + 3H2O = 2H3XO4
M = 18 g / mol
n = 8.1 / 18 = 0.45 mol
According to the reaction equation, oxide reacts 3 times less than water
n (X2O5) = n (H2O) / 3 = 0.45 / 3 = 0.15 mol
M (X2O5) = m / n = 34.5 / 0.15 = 230 g / mol, hence
M = 2 x + 80 g / mol
2 x + 80 = 230
x = 75 g / mol
As2O5