General Chemistry self-directed lab

General Chemistry self-directed lab - Self-Directed...

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Self-Directed Research Problem Introduction Two unknown samples were recovered uncontaminated, one of which is a coordination compound, the other being a salt. This experiment was conducted in order to determine the identity of these two unknown samples, to evaluate the kinetics of the coordination compound, and to test photosensitivity in the coordination compound. The coordination compound possibilities have been revealed by preliminary analysis to include [V(NH 3 ) 3 (NCS) 3 ], K[Cr(NH 3 ) 2 (NCS) 4 ], or K 2 [Co(NH 3 )(NCS) 5 ]. A coordination compound is composed of several ligands, or chemical groups, bonded to a central metal atom. The salt is either NH 4 Br, Ca(CH 3 COO) 2 , or PbSO 4 . One test that can be used to distinguish between the container with the coordination compound and the one with the salt is absorbance spectroscopy. This test would be used to establish whether or not the compound is colored. Coordination compounds would be colored due to electronic transitions by the absorption of light, while salts would normally be clear or white. Running an absorbance spectrum in the visible wavelength (400 to 700nm) for each compound should distinguish between a colored compound and an uncolored one. The salt should have no peaks in the visible wavelength range while the coordination compound should have at least one peak. Another test that can be used to distinguish between the vial with the coordination compound and the one with the salt is to measure the pH. The coordination compound would be predicted to have a pH of 7, because it should be neither acidic nor basic. An ammonium bromide solution should have a pH below 7 because the weak acid NH 4 + releases some H + ions into the water. A calcium acetate solution should have a pH above 7 because the weak base CH 3 COO -1 causes hydroxide ions to ionize from water. If the salt is lead sulfate, it will not dissolve in water. The electrical conductivity of a compound refers to the number of ions that dissociate when in aqueous solution. This can be calculated using a reading from a conductance probe, and can then be compared to the theoretical conductivities of known substances. This test was performed on both the coordination compound and the salt. For the coordination compound, the vanadium compound will have no ions, the chromium compound will have two ions, and the cobalt compound will have three ions. For the salt, ammonium bromide will have two ions, calcium acetate will have three ions, and lead sulfate will have no ions.
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The magnetic susceptibility of a compound refers to the amount of unpaired electrons in the d orbitals. There are two levels of d orbitals called the e orbitals and the t orbitals. When electrons split between these orbitals, it is referred to as crystal field splitting. The lower energy orbitals include dxy, dxz, and dyz, while the higher energy orbitals include dz 2 and dx 2 -y 2 . If the magnetic susceptibility reading is positive, all the electrons in the compound are paired. Diamagnetism refers to the absence of unpaired electrons.
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General Chemistry self-directed lab - Self-Directed...

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