Which reactions are used for the preparation of the halogen acid?

Options

A. `2KBr+ underset((conc.))(H_(2)SO_(4)) to K_(2)SO_(4)+2HBr`
B. `CaF_(2)+underset((conc.))(H_(2)SO_(4)) to CaSO_(4)+2HF`
C. `NaCl+underset((conc.))(H_(2)SO_(4)) to NaHSO_(4)+HCl`
D. `2KI+underset((conc.))(H_(2)SO_(4)) to K_(2)SO_(4)+2HI`

Answer

To prepare halogen acids, we can utilize specific reactions involving concentrated sulfuric acid (H2SO4) with halide salts. Here’s a step-by-step breakdown of the reactions used for the preparation of halogen acids:

### Step 1: Understand Halogen Acids
Halogen acids are binary acids formed from hydrogen and halogens (F, Cl, Br, I). The common halogen acids include:
- Hydrofluoric acid (HF)
- Hydrochloric acid (HCl)
- Hydrobromic acid (HBr)
- Hydroiodic acid (HI)

### Step 2: Identify the Reactions
We will examine the reactions that can lead to the formation of these halogen acids using concentrated sulfuric acid.

### Step 3: Analyze Each Reaction
1. **Reaction with Calcium Fluoride (CaF2)**:
- **Reaction**: CaF2 + H2SO4 → CaSO4 + 2HF
- This reaction produces hydrofluoric acid (HF).

2. **Reaction with Sodium Chloride (NaCl)**:
- **Reaction**: NaCl + H2SO4 → NaHSO4 + HCl
- This reaction produces hydrochloric acid (HCl).

3. **Reactions with Bromides and Iodides**:
- Concentrated H2SO4 cannot be used to prepare HBr and HI because it acts as a strong oxidizing agent and can oxidize HBr to Br2 and HI to I2. Therefore, these reactions are not suitable for preparing HBr and HI.

### Step 4: Conclusion
From the analysis, the valid reactions for the preparation of halogen acids using concentrated sulfuric acid are:
- **B**: CaF2 + H2SO4 → CaSO4 + 2HF (produces HF)
- **C**: NaCl + H2SO4 → NaHSO4 + HCl (produces HCl)

### Final Answer
The reactions used for the preparation of halogen acids are:
- Option B: CaF2 + H2SO4 → CaSO4 + 2HF
- Option C: NaCl + H2SO4 → NaHSO4 + HCl

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