10 g of potassium chloride with an admixture of potassium nitrate was dissolved in water and an excess of argentum nitrate solution was added, as a result of which a precipitate weighing 14.35 g was obtained. What is the mass fraction of impurities?
Let’s write down the reaction scheme: KCl + KNO3 (impurity) + AgNO3 = KNO3 + AgCl (precipitate)
As a result of the transformation, a precipitate of silver chloride and potassium nitrate were formed (as a reaction product and an impurity in the starting materials). Since the silver salt was in excess, knowing the amount of precipitate, you can calculate the mass of potassium chloride.
Find the amount of silver chloride substance n (AgCl) = m (AgCl) / M (AgCl), where m and M are the mass and molar mass of the component, respectively
n (AgCl) = 14.35 / 143.5 = 0.1 mol
It can be seen from the reaction equation that the amount of potassium chloride substance is n (KCl) = n (AgCl). Find the mass of potassium chloride in the original sample m (KCl) = n (KCl) * M (KCl) = 0.1 * 74.5 = 7.45 g
We calculate the mass of potassium nitrate impurity m (KNO3) = m (sample) – m (KCl) = 10 – 7.45 = 2.55 g
Determine the mass fraction of the impurity w = (m (KNO3) / m (sample)) * 100% = (2.55 / 10) * 100% = 25.5%
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