Question

Lithium hydride (LiH) is a source of hydride ion, shown below. \(\mathrm{H}\) : As you can see, the hydride ion has a negative charge (it is an anion) and a lone pair of electrons. When thrown into water, the hydride ion makes the water strongly basic. Write a reaction that shows how the hydride ion reacts with water to make the water basic. Then explain in English what the hydride ion does to water molecules to make the resulting solution basic.

Short answer

The hydride ion (H-) reacts with water (H2O) to form hydrogen gas (H2) and hydroxide ion (OH-), as represented by the balanced equation: \(\mathrm{H^{-} + H_{2}O \rightarrow H_{2} + OH^{-}}\). In this reaction, the hydride ion donates an electron to a hydrogen atom in water, producing hydrogen gas and leaving the oxygen atom with a negative charge, creating the hydroxide ion. The increasing presence of hydroxide ions makes the water more basic.

Step-by-step solution

Write the balanced chemical equation for the reaction of hydride ion and water

First, we will write the chemical equation of the hydride ion (H-) reacting with water (H2O). The products of this reaction are hydrogen gas (H2) and hydroxide ion (OH-), which makes the water more basic. The balanced chemical equation for the reaction is: \( \mathrm{H^{-} + H_{2}O \rightarrow H_{2} + OH^{-}} \)

Explain the reaction in English

The hydride ion (H-) has a lone pair of electrons and a negative charge. When it reacts with water (H2O), it donates an electron to one of the hydrogen atoms in water, which forms a covalent bond between the two hydrogen atoms, creating hydrogen gas (H2). The remaining oxygen atom in water is now left with a negative charge and forms a hydroxide ion (OH-). The presence of hydroxide ions in the solution increases the pH, thus making the water more basic.

Key concepts

lithium hydride (LiH)

Lithium hydride (\( \text{LiH} \)) is a chemical compound composed of lithium and hydrogen. In this compound, lithium is bonded to a hydride ion (\( \text{H}^- \)), which is basically a hydrogen atom with an extra electron. This extra electron gives the hydride ion a negative charge.

LiH is often used as a reducing agent because the hydride ion can easily donate an electron. When lithium hydride comes into contact with water, it releases hydride ions, which then participate in chemical reactions. These reactions, particularly with water, are what largely contribute to making the solutions more basic. The interaction of LiH with water results in the production of hydrogen gas and hydroxide ions.

basic solutions

A solution is considered basic if it has a pH greater than 7. The pH scale measures how acidic or basic a solution is, ranging from 0 to 14.

Basic solutions have high concentrations of hydroxide ions (\( \text{OH}^- \)) compared to hydrogen ions (\( \text{H}^+ \)).

• At a molecular level, bases are substances that can accept hydrogen ions or donate electron pairs.
• They often feel slippery to the touch and can change the color of certain indicators (like litmus paper) from red to blue.
• Common examples include household cleaning agents, ammonia, and baking soda.

When the hydride ion reacts with water, it increases the concentration of hydroxide ions, thereby increasing the pH and making the solution more basic.

chemical equations

Chemical equations are symbolic representations of chemical reactions. They show how reactants transform into products. Each element is represented by its chemical symbol, and the compounds are shown with their correct formulae.

A balanced chemical equation has the same number of each type of atom on both sides. This reflects the law of conservation of mass, meaning that mass cannot be created or destroyed in a chemical reaction.

• In the equation \( \text{H}^- + \text{H}_2\text{O} \rightarrow \text{H}_2 + \text{OH}^- \), it illustrates how the hydride ion reacts with water.
• The equation shows that one molecule of hydride ion and one molecule of water yield one molecule of hydrogen gas and one hydroxide ion.

This equation helps understand the fundamental changes occurring during the reaction, showcasing both the physical substances involved and the energy dynamics.

hydroxide ion (OH-)

The hydroxide ion, denoted as \( \text{OH}^- \), is a diatomic anion consisting of an oxygen atom and a hydrogen atom. It carries a negative charge.

Hydroxide ions are crucial in determining the basicity of a solution.

• A higher concentration of these ions typically means a more basic solution.
• They are the main contributors to creating basic or alkaline solutions and are responsible for increasing the pH of a solution above 7.

When a hydride ion reacts with water, it produces hydroxide ions, which then raises the solution's pH level. This makes hydroxide ions a key player in many chemical reactions, especially those involving bases.

anion

An anion is a negatively charged ion, meaning it has more electrons than protons. These extra electrons give the anion its negative charge.

Anions are typically formed when an atom gains one or more electrons. Common examples include chloride (\( \text{Cl}^- \)), sulfate (\( \text{SO}_4^{2-} \)), and, most relevantly, the hydride ion (\( \text{H}^- \)).

• They play crucial roles in various chemical processes, often taking part in reactions as reactants or products.
• Anions can combine with cations (positively charged ions) to form neutral compounds, like tables of salt \( \text{NaCl} \).

In the context of lithium hydride reacting with water, the hydride ion (an anion) initiates the reaction which results in a basic solution by forming hydroxide ions, another important anion in chemistry.