# To 150 solution with a mass fraction of magnesium nitrate 10% was added 15 grams of the same salt and 45 ml

To 150 solution with a mass fraction of magnesium nitrate 10% was added 15 grams of the same salt and 45 ml of water was evaporated. the mass fraction of salt in the solution is equal to.

Given:

m (Mg (NO3) 2 solution) = 150 g;

w% (Mg (NO3) 2) = 10%;

V (H2O) = 45 ml;

m (Mg (NO3) 2) = 15g;

To find:

w% (Mg (NO3) 2 in the final solution) -?

Decision:

1) Find the mass of magnesium nitrate in solution:

m (Mg (NO3) 2) = 150 g * 0.1 = 15 g;

2) Find the mass of evaporated water:

m (H2O) = p * V = 1 g / ml * 45 ml = 45 g;

3) Find the mass of the solution after adding a portion of salt and evaporating the water:

m (solution) = 150 g + 15 g – 45 g = 120 g;

4) Find the mass of salt after adding a portion:

m (Mg (NO3) 2) = 15 g + 15 g = 30 g

5) Find the mass fraction of magnesium nitrate in the final solution:

w% (Mg (NO3) 2) = m (Mg (NO3) 2): m (solution) * 100% = 30 g: 120 g * 100% = 25%.

Answer: w% (Mg (NO3) 2) = 25%.

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