Chemical Equilibrium Experimental Results

1838 Words Feb 2nd, 2013 8 Pages
Chemical Equilibrium



A. Iron-Silver Equilibrium

In studying equilibrium between iron and silver, 0.10 M FeSO4 and 0.10 M AgNO3 were used. The balanced equation for the reaction is:

FeSO4 (aq) + 2 AgNO3 (aq) ↔ Fe(NO3)2 (aq) + Ag2SO4 (s)

It has a net equation of:

Fe2+(aq) + Ag+(aq) ↔ Fe3+(aq) + Ag(s)

This part of the experiment required centrifugation of the solution. This was done to completely separate the precipitate from the supernate for easier decantation process.

In determining the presence of Fe2+ in the supernate, 0.10 M of K3Fe(CN)6 was used . The resulting
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This is because four (4) moles of NH3 are needed for every mole of Cu2+ present in the system in order to make the complex. Another reason is that as the complex is being formed by the four ligands that attach to the Cu2+ ion, the reaction simultaneously occur where the OH- ion is derived from the dissociation of NH3 into NH4+ and hydroxide and NH4+ does not attach to the Cu2+ ion. This makes the necessary amount of NH3 to be in excess in order to achieve the desired deep-blue copper-ammonia complex. The table below shows the number of drops of HCl and NH3 added:

Table 2. Data for copper-ammonia system

| Number of drops added | Color | Initial | | Pale blue | NH3 | 13 | Dark blue | HCl | 7 | Pale blue |

C. Chromate-Dichromate Equilibrium

For the Chromate-Dichromate part of the equilibrium experiment, K2CrO4 and K2Cr2O7 were used. At the beginning of the experiment, the chromate solution was yellow in color while the dichromate was orange.

When acid (H2SO4) was added, only the CrO42- species changed in color. While only Cr2O72- changed in color upon the addition of base (NaOH).

The chemical equation for the conversion of chromate to dichromate is:

2 K2CrO4(aq) + H2SO4(aq) ↔ K2Cr2O7(aq) + K2SO4(aq) + H2O(l) The conversion of dichromate to chromate solution is given in the equation:

K2Cr2O7(aq) + 2NaOH(aq) ↔ K2CrO4(aq) +
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