To solve the problem of how many cations will get precipitated when `Al^(3+)`, `Cu^(2+)`, `Ni^(2+)`, `Co^(2+)`, `Fe^(3+)`, `Ba^(2+)`, and `Zn^(2+)` are treated with concentrated HCl followed by `H2S`, we can follow these steps:
### Step 1: Understand the effect of concentrated HCl
When concentrated HCl is added to a solution containing cations, it primarily precipitates the cations of the first group. The first group cations typically include lead (Pb²⁺), silver (Ag⁺), and mercury (Hg²⁺). However, in this case, we do not have any of these cations present.
**Hint:** Concentrated HCl will precipitate cations that form insoluble chlorides. Identify which cations are affected.
### Step 2: Identify the cations present
The cations present in the solution are:
- `Al^(3+)`
- `Cu^(2+)`
- `Ni^(2+)`
- `Co^(2+)`
- `Fe^(3+)`
- `Ba^(2+)`
- `Zn^(2+)`
**Hint:** List all the cations and remember that not all will precipitate with HCl.
### Step 3: Determine the precipitation with HCl
Since none of the listed cations (Al³⁺, Cu²⁺, Ni²⁺, Co²⁺, Fe³⁺, Ba²⁺, Zn²⁺) form insoluble chlorides with concentrated HCl, there will be no precipitation from this step.
**Hint:** Check the solubility rules for chlorides to see which cations would precipitate.
### Step 4: Add H2S
After adding concentrated HCl, we then add `H2S`. The addition of H2S will precipitate the cations of the second group, which typically includes cations like Cu²⁺, Pb²⁺, and others that form insoluble sulfides.
**Hint:** Identify which cations can form insoluble sulfides when H2S is added.
### Step 5: Identify the cations that precipitate with H2S
From the list of cations:
- `Cu^(2+)` forms an insoluble sulfide (CuS).
- `Ni^(2+)`, `Co^(2+)`, and `Zn^(2+)` can also form sulfides, but they are not part of the second group in this context.
- `Al^(3+)`, `Fe^(3+)`, and `Ba^(2+)` do not precipitate with H2S.
Thus, only `Cu^(2+)` will precipitate as CuS.
**Hint:** Focus on the specific cations that are known to precipitate with H2S.
### Conclusion
In total, only **1 cation (Cu²⁺)** will precipitate when H2S is added after concentrated HCl.
**Final Answer:** 1 cation will get precipitated.
