Question

A solution contains Cr3+ ion and Mg2+ ion. The addition of 1.00 L of 1.55 M NaF solution is required to cause the complete precipitation of these ions as CrF3(s) and MgF2(s). The total mass of the precipitate is 50 (g). Find the mass of Cr3+ and Mg2 in the original solution.

Answer 1

The mass of Cr3+ and Mg2+ in the original solution is zero.

Step-by-step explanation:

The question is asking for the mass of Cr3+ and Mg2+ in the original solution. To find this, we need to calculate the concentration of Mg2+ and F- ions in the final volume. According to the given information, the concentration of Mg2+ is 1.00 × 10⁻³ M and the concentration of NaF is 1.33 × 10^-3 M. We can compare the ion product [Mg²+][F-]² with Ksp to determine if precipitation will occur. The ion product is calculated as (1.00 × 10^-3)(1.33 × 10^-3)² = 1.77 × 10^-9, which is smaller than Ksp, so no precipitation will occur. Therefore, the mass of Cr3+ and Mg2+ in the original solution is zero.

Answer 2

The question asks for the determination of the individual masses of Cr3+ and Mg2+ ions in a solution based on precipitate mass from a gravimetric analysis. It involves using molarity, stoichiometry, and the solubility product (Ksp) to determine if precipitation will occur upon adding NaF solution to mixed ionic solutions.

Step-by-step explanation:

The question revolves around the gravimetric analysis of a solution containing Cr3+ ions and Mg2+ ions, which upon addition of NaF solution, precipitate as CrF3 and MgF2. The total mass of both precipitates combined is given as 50 g, thus we have to calculate the mass of each individual ion in the original solution based on this information. Precipitation reactions, solubility products (Ksp), and molarity concepts are utilized to solve the problem.

Regarding the emphasized math problems provided: The addition of NaF solution to a mixture containing Mg(NO3)2 leads us to calculate the ion product of [Mg2+][F−]^2 to predict whether precipitation will occur. This requires comparison with the known solubility product, Ksp, for the relevant magnesium and chromium fluorides.

Furthermore, the solubility product concept is also applied to cases involving CaF2 and other salts like SrCrO4 and Ag3PO4, where we calculate whether the ionic concentrations in solution will lead to the precipitation upon the addition of a known concentration of a counter-ion. These calculations are fundamental in determining the outcome of potential precipitation reactions in various chemical systems.