Problem 75 - Chemistry Central Science

Question

A palladium complex formed from a solution containing bromide ion and pyridine, \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{~N}\) (a good electronpair donor), is found on elemental analysis to contain \(37.6 \%\) bromine, \(28.3 \%\) carbon, \(6.60 \%\) nitrogen, and \(2.37 \%\) hydrogen by mass. The compound is slightly soluble in several organic solvents; its solutions in water or alcohol do not conduct electricity. It is found experimentally to have a zero dipole moment. Write the chemical formula, and indicate its probable structure.

Step-by-Step Solution

Answer

The chemical formula of the palladium complex is \(\mathrm{PdBr_{2}(C_{5}H_{5}N)_{2}}\), and its probable structure is square planar, in which the palladium atom is coordinated to two bromine atoms and two pyridine ligands.

Step 1: Calculate the moles of each element

To determine the empirical formula of the complex, we need to find the moles of each element: bromine (Br), carbon (C), nitrogen (N), and hydrogen (H). Assume 100 g of the sample, so the mass percentages directly convert to grams. Moles of Br = \(\frac{37.6\,\text{g}}{79.904\,\text{g/mol}} = 0.471\) mol Moles of C = \(\frac{28.3\,\text{g}}{12.011\,\text{g/mol}} = 2.36\) mol Moles of N = \(\frac{6.60\,\text{g}}{14.007\,\text{g/mol}} = 0.471\) mol Moles of H = \(\frac{2.37\,\text{g}}{1.008\,\text{g/mol}} = 2.35\) mol

Step 2: Find the empirical formula

Now, we have to divide the moles of each element by the smallest value among them (0.471) to find the empirical formula. Moles of Br : \(\frac{0.471}{0.471} = 1\) Moles of C : \(\frac{2.36}{0.471} = 5\) Moles of N : \(\frac{0.471}{0.471} = 1\) Moles of H : \(\frac{2.35}{0.471} = 5\) Thus, the empirical formula is found to be: BrC₅H₅N

Step 3: Use the properties of the complex

Since the complex is non-conductive when dissolved in water or alcohol, it indicates that the complex is not ionic. The solubility in organic solvents further suggests that the complex has a covalent nature. Moreover, Pyridine (C₅H₅N) is known as a strong electron-pair donor.

Step 4: Consider the zero dipole moment

The zero dipole moment property suggests that the arrangement of atoms in the complex is likely symmetrical.

Step 5: Determine the probable structure

Given the empirical formula, BrC₅H₅N, and taking into account that Pyridine (C₅H₅N) is a strong electron-pair donor, we can determine that a probable structure for the palladium complex is PdBr₂(C₅H₅N)₂. In this structure, the palladium atom is coordinated to two bromine atoms and two pyridine ligands. The overall geometry of the complex is square planar, which is symmetrical, meeting the requirement of a zero dipole moment. Hence, the chemical formula of the palladium complex is \(\mathrm{PdBr_{2}(C_{5}H_{5}N)_{2}}\), and its probable structure is square planar, in which the palladium atom is coordinated to two bromine atoms and two pyridine ligands.