After the precipitation of the Group I cations as chlorides by the reaction with HCl, nearly all of the precipitate dissolves in hot water. Which ion(s) are present? Which ion(s) are absent?
Group I is Ag, Hg(+1), Pb.
PbCl2 is soluble in hot water. AgCl and Hg2Cl2 are not.
So ???? must be the ppt.
After the precipitation of Group I cations as chlorides by the reaction with HCl, nearly all of the precipitate dissolves in hot water. To determine which ions are present and which are absent, we need to understand the reactions involved.
Group I cations refer to the first group of cations in qualitative inorganic analysis, which includes Ag+, Pb2+, and Hg2+.
When a chloride solution is added to a solution containing Group I cations, a precipitation reaction occurs, forming chlorides:
Ag+ (aq) + Cl- (aq) → AgCl (s)
Pb2+ (aq) + 2Cl- (aq) → PbCl2 (s)
Hg2+ (aq) + 2Cl- (aq) → Hg2Cl2 (s)
However, it is known that these chlorides are soluble in hot water. Therefore, when hot water is introduced, the precipitate dissolves, releasing the cations back into the solution:
AgCl (s) + H2O (hot) → Ag+ (aq) + Cl- (aq)
PbCl2 (s) + H2O (hot) → Pb2+ (aq) + 2Cl- (aq)
Hg2Cl2 (s) + H2O (hot) → Hg2 2+ (aq) + 2Cl- (aq)
From these reactions, we can conclude that in hot water, the Ag+, Pb2+, and Hg2+ ions are present as soluble cations.
The chloride ions (Cl-) are absent in the hot water solution as they are part of the original precipitate that dissolves.
To summarize, the ions present in the hot water solution are Ag+, Pb2+, and Hg2+, while the chloride ions are absent.
To determine which ion(s) are present and which ion(s) are absent after the precipitation of Group I cations as chlorides followed by dissolving the precipitate in hot water, we need to understand the properties of Group I cations and their respective chlorides.
Group I cations include silver (Ag+), lead (Pb2+), mercury(I) (Hg22+), and mercury(II) (Hg2+). These cations form insoluble chlorides when reacted with hydrochloric acid (HCl) in aqueous solution.
When the precipitate is dissolved in hot water, it is important to note that solubility can change with temperature. In this case, hot water is used because it increases the solubility of the chloride precipitate.
Here's a step-by-step explanation of how to determine the ions present and absent:
1. Start by considering the individual chlorides of the Group I cations and their solubility in water:
- Silver chloride (AgCl) is sparingly soluble in water.
- Lead chloride (PbCl2) is soluble in hot water.
- Mercury(I) chloride (Hg2Cl2) is insoluble in cold water but soluble in excess chloride ions (due to the formation of Hg2Cl42- complex) and slightly soluble in hot water.
- Mercury(II) chloride (HgCl2) is slightly soluble in cold water and soluble in hot water.
2. Based on the given information, we can conclude the following:
- The silver chloride precipitate dissolves in hot water, indicating the presence of Ag+ ions in the solution.
- The lead chloride precipitate does not dissolve in hot water, indicating the absence of Pb2+ ions in the solution.
- The mercury(I) chloride precipitate dissolves in hot water, indicating the presence of Hg22+ ions in the solution.
- The mercury(II) chloride precipitate slightly dissolves in hot water, indicating the presence of Hg2+ ions in the solution.
To summarize:
- Ag+ ions are present.
- Pb2+ ions are absent.
- Hg22+ ions are present.
- Hg2+ ions are present.
Remember, this explanation was based on the solubility properties of the chlorides at different temperatures. It is always good practice to refer to reliable sources and experimental data for accurate information.