With the complete dissociation of 8.55 g of the Xn (YO4) m salt, 0.05 mol of Xm (+) and 0.075 mol of (YO4) n (-) ions are formed.

With the complete dissociation of 8.55 g of the Xn (YO4) m salt, 0.05 mol of Xm (+) and 0.075 mol of (YO4) n (-) ions are formed. Determine the molar mass of this salt in g / mol.

Given:
m (Xn (YO4) m) = 8.55 g
n (Xm (+)) = 0.05 mol
n ((YO4) n (-)) = 0.075 mol

Find:
Mr (Xn (YO4) m) -?

Solution:
1) The ratio between the number of ions forming the Xn (YO4) m molecule is determined by the ratio of the chemical amount of each of the ions as a result of complete dissociation:
n: m = n (Xm (+)): n ((YO4) n (-)) = 0.05: 0.075 = 1: 1.5;
Since the number of ions must be an integer, then
n: m = 2: 3;

2) Find the amount of substance Xn (YO4) m (by definition):
n (Xn (YO4) m) = n (Xm (+)) / 2 = n ((YO4) n (-)) / 3 = 0.05 / 2 = 0.075 / 3 = 0.025 mol;

3) Find the molar mass of the substance Xn (YO4) m:
Mr (Xn (YO4) m) = m (Xn (YO4) m) / n (Xn (YO4) m) = 8.55 / 0.025 = 342 g / mol.

Answer: The molar mass of the substance Xn (YO4) m is 342 g / mol.