Problem 96 - Chemistry Matter and Change

Question

Complete the following chemical equations. $$\begin{array}{l}{\text { a. } \mathrm{Na}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(1) \rightarrow} \\ {\text { b. } \mathrm{K}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(1) \rightarrow}\end{array}$$

Step-by-Step Solution

Answer

a. \(2\mathrm{Na(s)} + 2\mathrm{H}_2\mathrm{O(l)} \rightarrow 2\mathrm{NaOH(aq)} + \mathrm{H}_2\mathrm{(g)}\) b. \(2\mathrm{K(s)} + 2\mathrm{H}_2\mathrm{O(l)} \rightarrow 2\mathrm{KOH(aq)} + \mathrm{H}_2\mathrm{(g)}\)

Step 1: Reactants Observation

In the first equation, we have sodium \( \text{(Na)} \) reacting with water \( \text{(H}_2\text{O}) \). In the second equation, we have potassium \( \text{(K)} \) reacting with water. Notice how both metals are alkali metals, which generally react with water to form a metal hydroxide and hydrogen gas.

Step 2: Na and Water Reaction

When sodium \( \text{(Na)} \) reacts with water, the reaction produces sodium hydroxide \( \text{(NaOH)} \) and hydrogen gas \( \text{(H}_2) \). The balanced chemical equation is: \[ \text{2Na(s)} + \text{2H}_2\text{O(l)} \rightarrow \text{2NaOH(aq)} + \text{H}_2\text{(g)} \] Each sodium atom donates an electron to water, resulting in the formation of sodium hydroxide and releasing hydrogen gas.

Step 3: K and Water Reaction

Potassium \( \text{(K)} \), similarly to sodium, reacts with water to form potassium hydroxide \( \text{(KOH)} \) and hydrogen gas. The balanced chemical equation is: \[ \text{2K(s)} + \text{2H}_2\text{O(l)} \rightarrow \text{2KOH(aq)} + \text{H}_2\text{(g)} \] Potassium is more reactive than sodium and follows a similar electron transfer process leading to the formation of potassium hydroxide and hydrogen gas.

Key Concepts

Alkali Metals

Alkali metals are an intriguing group of elements found in Group 1 of the periodic table. They share common characteristics, such as being highly reactive, especially with water. Let's consider some key aspects:

• Alkali metals from lithium (Li) to francium (Fr), have a single electron in their outermost shell. This makes them incredibly eager to give away that one electron, leading to their high reactivity.
• They are typically soft and can be cut with a knife. These metals also have low melting points compared to other metals.
• When engaging with chemical reactions, alkali metals tend to form positive ions, often denoted in chemical reactions as M⁺, where M stands for the metal.

Their reactions with other elements are vital for various chemical processes, especially when considering their interactions with water.

Metal-Water Reactions

When alkali metals react with water, a fascinating process occurs. Water, in its liquid form, has the molecular composition of H₂O. Here are some detailed processes:

• Upon contact with water, alkali metals such as sodium and potassium undergo a vigorous reaction. The metal donates its outer electron to the water's molecules.
• This electron transfer process results in the formation of metal hydroxides, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), depending on the metal involved.
• Additionally, hydrogen gas (H₂) is released as a by-product. It's often visible as bubbling and can even ignite due to the reaction's exothermic nature.

The balanced chemical equations, like the ones shown earlier, highlight these transformations and the specific ratios needed to balance the reactants and products.

Chemical Reactivity

Chemical reactivity refers to how readily a substance undergoes a chemical change. It's an essential concept in understanding why certain elements react more vigorously than others. For alkali metals, their reactivity increases as you move down the group in the periodic table.

• Potassium, for instance, is more reactive than sodium. This greater reactivity is due to potassium's outer electron being further from the nucleus, making it easier for the atom to lose it during a reaction.
• The exothermic nature of these reactions, with heat often released in the process, emphasizes the reactivity level. It's not uncommon for such reactions to cause flames when the hydrogen produced ignites.
• Alkali metals' reactivity is crucial in various applications, from energy production using hydrogen gas to manufacturing processes relying on metal hydroxides.

Understanding chemical reactivity gives insight into the behaviors and applications of different substances in science and industry.