When the unknown was tested with silver nitrate a solid was produced, but also the color was a light yellow that is quite similar to the description of the product of sodium iodide added to silver nitrate (a dull but light yellow). This color was not exactly similar to the colors formed from other combinations as they were “slightly yellow” for the formula 2AgNO3(aq)+NaCO3(aq) →AgCO3(s)+2NaNO3(aq) , “white” for 2AgNO3(aq)+NaC2O4(aq) →AgC2O4(s)+2NaNO3(aq) , and “yellowish” for 3AgNO3(aq)+Na3PO4(aq) →Ag3PO4(s)+3NaNO3(aq). A solid was formed in both situations due to a cloudy substance that formed with the silver nitrate + sodium iodide and the unknown + silver nitrate. It makes sense that a solid was formed because:
AgNO3(aq)+NaI(aq) →AgI(s)+NaNO3(aq)
On the back of the periodic table it states that if the anion I- is part of the compound then cations like Ag+ and Pb2+ will form a solid with it. Since it is AgI, a solid is clearly formed.
When the unknown was tested with cobalt (II) nitrate a solid was not produced and there was no color change it was the same light pink as originally, similar to the description of the product of sodium iodide added to cobalt (II) nitrate which was same light pink as the original color of the mixture. A solid was not formed in both situations because:
Co(NO3)2(aq)+2NaI(aq) →CoI2(aq)+2NaNO3(aq)
According to the back of the periodic table it states that if the anion iodine is part of the compound then cations like Ag+, Pb2+, Hg22+, and Cu+ will form a solid with it, but iodine with all other cations form an aqueous solution. Therefore, since cobalt is not listed as one of the cations that iodine forms a solid with, no solid would be formed which is exactly what happened when sodium iodide was added to cobalt (II) nitrate and no other combination with cobalt (II) nitrate. Since sodium iodide in combination with cobalt (II) nitrate was the only one involving cobalt (II) nitrate that did not have a reaction it proves that the unknown is one of the two. But, since it has been proven that unknown is an anion, sodium iodide is our only option.
When the unknown was tested with copper (II) nitrate a solid was produced, but also the color was a dark orange-yellow that was not too cloudy. This description is basically the same as the description of the product of sodium iodide added to copper (II) nitrate which was "dark yellow/range tone, copper color, slightly cloudy". A solid was formed in both situations because it was slightly cloudy in both situations.
Cu(NO3)2 (aq)+2NaI(aq) → CuI2(s)+2NaNO3(aq)
According to the back of the periodic table it states that if the anion iodine is part of the compound then cations like Ag+, Pb2+, Hg22+, and Cu+ will form a solid with it. Therefore, since copper is listed as one of the cations that iodine forms a solid with, a solid would be formed which is exactly what happened when sodium iodide was added to copper (II) nitrate. Since sodium iodide in combination with copper (II) nitrate was the only combination to form a dark yellow/orange color of all 4 anions in combination with the cation copper (II) nitrate sodium iodide seems the only option for the unknown. It is also not probable that the unknown is copper (II) nitrate because if there is a precipitate and a color change, it would not be the same color because different formulas yield different reactions like the colors formed. They are all unique.
