To a solution weighing 10 grams with a mass fraction of hydrogen chloride 10% was added a solution weighing 4 grams

To a solution weighing 10 grams with a mass fraction of hydrogen chloride 10% was added a solution weighing 4 grams with a mass fraction of hydrogen chloride 25%. Determine the mass fraction of HCl in the resulting solution.

Given:
m1 (solution) = 10g
w1 (HCl) = 10%
m2 (solution) = 4g
w2 (HCl) = 25%
Find: w (HCl)
Decision
m1 (solution) = 10g
m1 (HCl) = m1 (solution) * w1 (HCl)
m1 = 10 * 10/100 = 1g
m2 (HCl) = 4 * 25/100 = 1g
m (solution) = m1 + m2 is the sum of the masses of the solution
m (solution) = 10 + 4 = 14 (g)
m (salt) = 1 + 1 = 2g
w (HCl) = m (salt) / m (solution)
m (HCl) = 2: 14 = 14.28%