Calculate the mass of the salt that is formed by the interaction of magnesium with 20% nitric acid weighing 250 grams.

Given:

m (HNO3) = 250 g

w% (HNO3) = 20%

To find:

m (salt) -?

Decision:

2HNO3 + Mg = H2 + Mg (NO3) 2, – we solve the problem, relying on the composed reaction equation:

1) Find the mass of the acid in the solution that has reacted:

m (HNO3) = 250 g * 0.2 = 50 g

2) Find the amount of acid:

n (HNO3) = m: M = 50 g: 63 g / mol = 0.8 mol

3) We compose a logical expression:

If 2 mol of HNO3 gives 1 mol of Mg (NO3) 2,

then 0.8 mol of HNO3 will give x mol of Mg (NO3) 2,

then x = 0.4 mol.

4) Find the mass of magnesium nitrate formed during the reaction:

m (Mg (NO3) 2) = n * M = 0.4 mol * 148 g / mol = 59.2 g.

Answer: m (Mg (NO3) 2) = 59.2 g.