Question

Hydride ion: (a) Is a strong conjugate base of \(\mathrm{H}_{2}\) (b) Is a strong conjugate acid of \(\mathrm{H}_{2}\) (c) Is a strong conjugate base of \(\mathrm{H}^{-}\) (d) Is a strong conjugate acid of \(\mathrm{H}^{+}\)

Short answer

(a) Is a strong conjugate base of \( \mathrm{H}_{2} \).

Step-by-step solution

Understand the Context

Start by noting that the hydride ion is represented as \( \mathrm{H}^{-} \). A conjugate base is formed when an acid loses a proton, while a conjugate acid is formed when a base gains a proton. We're asked to identify what the hydride ion is a strong conjugate base or acid of.

Evaluate Each Option

Analyze each option:(a) The hydride ion \( \mathrm{H}^{-} \) is not a conjugate base of \( \mathrm{H}_{2} \), because \( \mathrm{H}_{2} \) is a neutral molecule and does not dissociate to produce \( \mathrm{H}^{-} \).(b) The hydride ion \( \mathrm{H}^{-} \) is also not a conjugate acid of \( \mathrm{H}_{2} \) because \( \mathrm{H}_{2} \) does not gain a proton.(c) The statement "is a strong conjugate base of \( \mathrm{H}^{-} \)" doesn't make chemical sense because a species cannot be a conjugate base of itself.(d) The hydride ion \( \mathrm{H}^{-} \) is indeed a strong conjugate base of \( \mathrm{H}_{2} \) or a very weak conjugate base of \( \mathrm{H}^{0} \), but not a conjugate acid of \( \mathrm{H}^{+} \), as it forms \( \mathrm{H}_{2} \) with a proton, not \( \mathrm{H}^{+} \). Thus hydride ion itself \( \mathrm{H}^{-} \) behaves as a base that gains a proton to form \( \mathrm{H}_{2} \).

Identify the Correct Answer

The correct option is (a). The hydride ion \( \mathrm{H}^{-} \) is a strong conjugate base of molecular hydrogen \( \mathrm{H}_{2} \), which means it can readily gain a proton to form \( \mathrm{H}_{2} \).

Key concepts

Conjugate base

When an acid donates a proton, the species that is left behind is known as its conjugate base. A conjugate base is essentially what remains of the acid after it has released its proton. This base can potentially gain a proton to convert back into the acid.
For instance, consider the molecule hydrogen ( \( \mathrm{H}_{2} \)). When a proton ( \( \mathrm{H}^{+} \)) is removed from \( \mathrm{H}_{2} \), what remains is the hydride ion ( \( \mathrm{H}^{-} \)). Thus, the hydride ion is the conjugate base of molecular hydrogen because it is left behind after \( \mathrm{H}_{2} \) donates a proton.
The strength of a conjugate base can be an indicator of the stability of the original acid. A strong conjugate base, like the hydride ion, implies that the acid was quite weak in holding onto its proton. Conversely, if the conjugate base is weak, the original acid is strong.

• A conjugate base forms when an acid loses a proton.
• The hydride ion ( \( \mathrm{H}^{-} \)) is a strong conjugate base of \( \mathrm{H}_{2} \).

Proton transfer

Proton transfer is a central concept in understanding acid-base reactions. It involves the movement of a proton ( \( \mathrm{H}^{+} \)) from one molecule to another. This transfer is what forms the basis of most acid-base reactions.
During proton transfer, acids donate protons while bases accept them. In the case of the hydride ion, when it interacts with an additional proton, it takes the proton up to form molecular hydrogen ( \( \mathrm{H}_{2} \)). The reverse process happens when \( \mathrm{H}_{2} \) donates a proton, producing the hydride ion.
Proton transfer reactions demonstrate how acids and bases react in a reversible manner.
This type of reaction is often fast and can occur many times, showing the dynamic nature of chemical processes.

• Protons are transferred from acids to bases in reactions.
• Hydride ions accept protons to form \( \mathrm{H}_{2} \).

Acid-base reaction

Acid-base reactions are chemical processes in which acids and bases interact, primarily through the transfer of protons. These reactions are essential for understanding how different compounds behave in various environments.
In an acid-base reaction, the acid donates a proton to the base. This leads to the formation of a conjugate base from the acid and a conjugate acid from the base. For example, the hydride ion as a base accepts a proton to become \( \mathrm{H}_{2} \), forming an acid-base pair.
This cycle of donating and accepting protons underpins a broad range of chemical reactions in both natural and industrial processes. It's crucial to realize that these reactions are reversible, and the equilibrium depends on the relative strengths of the acids and bases involved.

• Acid-base reactions involve the interaction of protons between reactions.
• The hydride ion ( \( \mathrm{H}^{-} \)) acts as a base in these reactions by accepting a proton.