A chemistry student needs to determine the composition of a sample that contains an unknown mixture of sodium chloride (NaCl) and potassium chloride (KCl). The student weighs 2.00 g of the mixture and dissolves it in water to obtain a solution. The student then precipitates the chloride ions from the solution with excess silver nitrate (AgNO3) to obtain 6.50 g of silver chloride (AgCl). Using mass balance calculations, determine the mass and percentage composition of the sodium chloride and potassium chloride in the mixture.

Question

A chemistry student needs to determine the composition of a sample that contains an unknown mixture of sodium chloride (NaCl) and potassium chloride (KCl). The student weighs 2.00 g of the mixture and dissolves it in water to obtain a solution. The student then precipitates the

Answer 1

To solve this problem, we can use the concept of mass balance and stoichiometry. First, we need to find the moles of chloride ions  Cl-  in the sample using the mass of silver chloride  AgCl  obtained.The molar mass of AgCl = 107.87  Ag  + 35.45  Cl  = 143.32 g/molNow, we can find the moles of AgCl:moles of AgCl = mass of AgCl / molar mass of AgClmoles of AgCl = 6.50 g / 143.32 g/mol = 0.0453 molSince the reaction between chloride ions and silver nitrate is a 1:1 ratio, the moles of Cl- ions in the sample are also 0.0453 mol.Now, let's assume that the mass of NaCl in the sample is x grams and the mass of KCl is  2.00 - x  grams.The molar mass of NaCl = 22.99  Na  + 35.45  Cl  = 58.44 g/molThe molar mass of KCl = 39.10  K  + 35.45  Cl  = 74.55 g/molWe can now find the moles of Cl- ions from NaCl and KCl:moles of Cl- from NaCl = x g / 58.44 g/molmoles of Cl- from KCl =  2.00 - x  g / 74.55 g/molSince the total moles of Cl- ions in the sample are 0.0453 mol, we can write the equation:moles of Cl- from NaCl + moles of Cl- from KCl = 0.0453 molSubstituting the expressions for moles of Cl- from NaCl and KCl, we get: x / 58.44  +   2.00 - x  / 74.55  = 0.0453Now, we can solve for x:x  1.22 gSo, the mass of NaCl in the sample is approximately 1.22 g, and the mass of KCl is:2.00 g - 1.22 g  0.78 gNow, we can find the percentage composition of NaCl and KCl in the mixture:% NaCl =  mass of NaCl / total mass of the mixture   100% NaCl   1.22 g / 2.00 g   100  61%% KCl =  mass of KCl / total mass of the mixture   100% KCl   0.78 g / 2.00 g   100  39%Therefore, the composition of the mixture is approximately 61% sodium chloride  NaCl  and 39% potassium chloride  KCl .