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Chapter 20: Problem 47

A student in 1895 prepared three chromium coordination compounds having the same formulas of \(\mathrm{CrCl}_{3}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\) with these properties: Write modern formulas for these compounds and suggest a method for confirming the number of \(\mathrm{Cl}^{-}\) ions present in solution in each case. (Hint: Some of the compounds may exist as hydrates, which are compounds that have a specific number of water molecules attached to them. The \(\mathrm{Cr}\) has a coordination number of 6 in all three compounds.)

Short Answer

Expert verified
The modern formulas for the three different Chromium compounds are: \[ \mathrm{[Cr(H_2O)_6]Cl_3} \], \[ \mathrm{[Cr(H_2O)_5Cl]Cl_2 \cdot H_2O} \] and \[ \mathrm{[Cr(H_2O)_4Cl_2]Cl \cdot 2H_2O} \]. The number of Cl- ions can be confirmed by adding silver nitrate to the solution of these compounds, creating a white precipitate of AgCl, which can be measured to determine the amount of chloride ions.

Step by step solution

01

Understanding Chromium Coordination Compounds

The coordination compounds of chromium (III) in this question involve six ligands. Five out of these six ligands are water molecules and the sixth is chloride ion. The variance between these compounds is majorly due to different chloride ion locations.
02

Writing Modern Formulas

The modern formulas for these compounds can be given as follows: \n\n1. \[ \mathrm{[Cr(H_2O)_6]Cl_3} \] - In this compound, three chloride ions are not directly bonded to the chromium ion.\n2. \[ \mathrm{[Cr(H_2O)_5Cl]Cl_2 \cdot H_2O} \] - Here, one of the chloride ions is directly bonded to chromium, hence, a part of the coordination sphere. The other two chlorides and water molecule are outside the coordination sphere.\n3. \[ \mathrm{[Cr(H_2O)_4Cl_2]Cl \cdot 2H_2O} \] - In this third compound, two chloride ions are directly bonded to the chromium ion and the last chloride ion and two water molecules are outside the coordination sphere.
03

Confirming the number of Cl- ions

To confirm the number of \(\mathrm{Cl}^{-}\) ions in each compound, a simple precipitation reaction can be conducted. Once these compounds are dissolved in water, the \(\mathrm{Cl}^{-}\) ions separate and when silver nitrate (AgNO3) is added, it reacts with the chloride ions to create a white precipitate of silver chloride (AgCl). By comparing the amount of precipitate formed in each case, the number of \(\mathrm{Cl}^{-}\) ions can be identified. More the ions, more will be the precipitate.

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Most popular questions from this chapter

Give the oxidation numbers of the metals in these species: (a) \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) (b) \(\mathrm{K}_{3}\left[\mathrm{Cr}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]\) (c) \(\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}\)

Give the oxidation numbers of the metals in these species: (a) \(\mathrm{Na}_{2} \mathrm{MoO}_{4}\) (b) \(\mathrm{MgWO}_{4}\), (c) \(\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\)

Why do transition metals have more oxidation states than other elements? Give the highest oxidation states for scandium to copper.

Compounds containing the \(\mathrm{Sc}^{3+}\) ion are colorless, whereas those containing the \(\mathrm{Ti}^{3+}\) ion are colored. Explain.

Copper is also known to exist in +3 oxidation state, which is believed to be involved in some biological electron transfer reactions. (a) Would you expect this oxidation state of copper to be stable? Explain. (b) Name the compound \(\mathrm{K}_{3} \mathrm{CuF}_{6}\) and predict the geometry of the complex ion and its magnetic properties. (c) Most of the known Cu(III) compounds have square planar geometry. Are these compounds diamagnetic or paramagnetic?
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