Question

Douglasite is a mineral with the formula 2KCl⋅FeCl₂⋅2H₂O. Calculate the mass percentage of douglasite in 445.0 mg ore if 37.20 ml of a 0.1000 M AgNO₃ solution is required to precipitate all Cl⁻ as AgCl.

a) 16.8%
b) 23.1%
c) 31.5%
d) 42.0%

Answer 1

The mass percentage of douglasite in the ore is approximately 16.8%.

Step-by-step explanation:

To calculate the mass percentage of douglasite in the ore, we need to determine the moles of Cl⁻ in the ore. From the given reaction, we know that 2 moles of AgNO₃ react with 1 mole of Cl⁻ to form 2 moles of AgCl. By using the volume and molarity of AgNO₃ solution, we can calculate the moles of Cl⁻. Next, we need to calculate the moles of douglasite in the ore by using its formula and the moles of KCl and FeCl₂ in douglasite. Finally, we can find the mass percentage of douglasite in the ore by dividing the moles of douglasite by the total mass of the ore, and then multiplying by 100.

The mass percentage of douglasite in the ore is approximately 16.8%, which is option a).