Question

Alkali metal hydrides react with water to give (1) acidic solution (2) basic solution (3) neutral solution (4) hydride ion

Short answer

Basic solution

Step-by-step solution

- Identify Alkali Metal Hydride

An alkali metal hydride is a compound formed between an alkali metal (Group 1 element) and hydrogen. Examples include sodium hydride (NaH), potassium hydride (KH), etc.

- React with Water

When an alkali metal hydride reacts with water, it forms the corresponding metal hydroxide and hydrogen gas. For example:NaH + H_2O -> NaOH + H_2

- Nature of the Solution

The resulting metal hydroxide, like NaOH, is a strong base. This means that the solution will be basic because metal hydroxides dissociate in water to produce hydroxide ions (OH^-).

- Conclude with the Product Type

Given the reaction, the product contains hydroxide ions which make the solution basic. Hence, the correct answer is a basic solution.

Key concepts

acidic solution

An acidic solution is created when a substance increases the concentration of hydrogen ions (H+) in water. These solutions have a pH level less than 7. Acids like hydrochloric acid (HCl) or sulfuric acid (H2SO4), when dissolved in water, release H+ ions and therefore make the solution acidic.

When alkali metal hydrides react with water, the substances they form do not release H+ ions. Instead, they release hydroxide ions (OH-), which makes the solution basic rather than acidic. It's important to understand that the nature of the products determines the type of solution we get.

basic solution

A basic solution is formed when a substance increases the concentration of hydroxide ions (OH-) in water. These solutions have a pH level greater than 7. Bases like sodium hydroxide (NaOH) or potassium hydroxide (KOH) dissociate in water to produce OH- ions, making the solution basic.

As seen in the reaction of alkali metal hydrides with water:\[ \text{NaH} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2 \]The resulting product is NaOH, which dissociates to provide OH- ions:

\[ \text{NaOH} \rightarrow \text{Na}^+ + \text{OH}^- \]These OH- ions are responsible for the basic nature of the solution. This property is why the reaction between alkali metal hydrides and water always produces a basic solution.

metal hydroxide

Metal hydroxides are compounds formed between metal ions and hydroxide ions (OH-). They are commonly produced in reactions involving metal oxides and water or metal hydrides and water. Typical metal hydroxides include sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2).

When alkali metal hydrides like sodium hydride (NaH) or potassium hydride (KH) react with water, they form the corresponding metal hydroxide:

\[ \text{NaH} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2 \]
\[ \text{KH} + \text{H}_2\text{O} \rightarrow \text{KOH} + \text{H}_2 \]
The metal hydroxides formed are strong bases, meaning they dissociate completely in water to release hydroxide ions (OH-). This dissociation is crucial because hydroxide ions are what make the solution basic.

Understanding the behavior of metal hydroxides helps in predicting the outcomes of their reactions and the nature of the resulting solutions.