Potassium chloride (KCl) has molar masses of 39.10 g mol⁻¹ for K and 35.45 g mol⁻¹ for Cl
CHEMISTRY · Single correct · CBSE · Chemistry · Some Basic Concepts of Chemistry · Some Basic Concepts of Chemistry
Problem
Potassium chloride (KCl) has molar masses of 39.10 g mol⁻¹ for K and 35.45 g mol⁻¹ for Cl. Three student groups prepared what they believed was pure KCl and recorded the following data.
• Sample I: 1.00 g K and 0.91 g Cl
• Sample II: 2.00 g K and 1.85 g Cl
• Sample III: 1.50 g K and 1.10 g Cl
Assuming one sample may contain an impurity, which sample most clearly deviates from the expected composition, and therefore is least likely to be pure KCl?
(a) Sample II, because the masses of K and Cl in a 1:1 compound should be equal, and Sample II shows the largest difference.
(b) All three samples differ by less than 2% from one another, so they are all equally likely to be pure KCl.
(c) Sample III, because its chlorine-to-potassium mass ratio deviates the most from the theoretical value for pure KCl.
(d) Sample I, because its smaller total mass means any weighing error has the greatest relative impact on its composition.