How many of the following pairs are conjugate acid/base pairs?
`HCl,Cl^(-)`
`KH,KCl`
`H_(2)SO_(4),Na_(2)SO_(4)`
`NaHS,Na_(2)S`
`CH_(3)COOH,CH_(3)COOH_(2)^(+)`
`Na_(2)CO_(3),NaHCO_(3)`
`NH_(3),NH_(4)Br`
`HCl,ClOH`
Aniline, anilinium

Answer

To determine how many of the given pairs are conjugate acid/base pairs, we need to understand the concept of conjugate acids and bases. According to the Brønsted-Lowry theory, an acid is a proton donor and a base is a proton acceptor. When an acid donates a proton (H⁺), it becomes its conjugate base, and when a base accepts a proton, it becomes its conjugate acid.

Let's analyze each pair:

1. **HCl, Cl⁻**:
- HCl donates a proton to become Cl⁻.
- **Conjugate pair**: Yes.

2. **KH, KCl**:
- KH is a salt that does not act as an acid or base in this context. KCl is a neutral salt and does not have a conjugate acid/base relationship.
- **Conjugate pair**: No.

3. **H₂SO₄, Na₂SO₄**:
- H₂SO₄ is a strong acid, while Na₂SO₄ is a salt. They do not have a direct acid/base relationship.
- **Conjugate pair**: No.

4. **NaHS, Na₂S**:
- NaHS can act as a weak acid (donating H⁺) to become Na₂S, which does not have a corresponding acid/base relationship.
- **Conjugate pair**: No.

5. **CH₃COOH, CH₃COOH₂⁺**:
- CH₃COOH (acetic acid) can donate a proton to become CH₃COO⁻ (its conjugate base), but CH₃COOH₂⁺ is not the conjugate base of CH₃COOH.
- **Conjugate pair**: No.

6. **Na₂CO₃, NaHCO₃**:
- Na₂CO₃ can donate a proton to become NaHCO₃. NaHCO₃ can accept a proton to become H₂CO₃.
- **Conjugate pair**: Yes.

7. **NH₃, NH₄Br**:
- NH₃ is a base that can accept a proton to become NH₄⁺ (ammonium ion). NH₄Br is a salt and does not represent a conjugate acid/base relationship.
- **Conjugate pair**: No.

8. **HCl, ClOH**:
- HCl donates a proton to become Cl⁻, while ClOH is not a direct conjugate of HCl.
- **Conjugate pair**: No.

9. **Aniline, Anilinium**:
- Aniline (C₆H₅NH₂) can accept a proton to become anilinium ion (C₆H₅NH₃⁺).
- **Conjugate pair**: Yes.

Now, let's summarize the results:

- Pairs that are conjugate acid/base pairs:
1. HCl, Cl⁻
2. Na₂CO₃, NaHCO₃
3. Aniline, Anilinium

Thus, there are **3 conjugate acid/base pairs** in total.