Problem 5 - Basic Principles of Organic Chemistry

Question

Write balanced equations for the reactions of (a) metallic sodium with water, (b) metallic sodium with methanol, (c) sodium hydride with water, and (d) sodium hydride with ethanol.

Step-by-Step Solution

Answer

Write balanced equations for (a) 2Na + 2H₂O → 2NaOH + H₂, (b) 2Na + 2CH₃OH → 2CH₃ONa + H₂, (c) NaH + H₂O → NaOH + H₂, and (d) NaH + C₂H₅OH → C₂H₅ONa + H₂.

Step 1: Reaction of Metallic Sodium with Water

When sodium (Na) reacts with water (H₂O), it produces sodium hydroxide (NaOH) and hydrogen gas (H₂). The balanced chemical equation is:\[2 \, \text{Na} + 2 \, \text{H}_2\text{O} \rightarrow 2 \, \text{NaOH} + \text{H}_2 \uparrow\]

Step 2: Reaction of Metallic Sodium with Methanol

Sodium reacts with methanol (CH₃OH) to form sodium methoxide (CH₃ONa) and hydrogen gas (H₂). The balanced chemical equation is:\[2 \, \text{Na} + 2 \, \text{CH}_3\text{OH} \rightarrow 2 \, \text{CH}_3\text{ONa} + \text{H}_2 \uparrow\]

Step 3: Reaction of Sodium Hydride with Water

Sodium hydride (NaH) reacts with water to produce sodium hydroxide (NaOH) and hydrogen gas (H₂). The balanced chemical equation is:\[\text{NaH} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2 \uparrow\]

Step 4: Reaction of Sodium Hydride with Ethanol

Sodium hydride reacts with ethanol (C₂H₅OH) to produce sodium ethoxide (C₂H₅ONa) and hydrogen gas (H₂). The balanced chemical equation is:\[\text{NaH} + \text{C}_2\text{H}_5\text{OH} \rightarrow \text{C}_2\text{H}_5\text{ONa} + \text{H}_2 \uparrow\]

Key Concepts

Balancing Chemical Equations

Balancing chemical equations is an essential skill in chemistry that ensures the same number of atoms for each element are present on both sides of a reaction. This is crucial because it adheres to the law of conservation of mass, stating that matter cannot be created or destroyed. When balancing an equation, you adjust the coefficients (numbers before the molecules) to achieve balance, but the subscripts within a chemical formula must remain unchanged.

Here's a simple step-by-step approach to balance an equation:

• Identify each element present in the reactants and products.
• List the number of atoms of each element on both sides of the equation.
• Use coefficients to balance the elements, starting with the most complex molecule.
• Check your work to confirm that the number of atoms for each element is equal on both sides.

Using these steps allows chemists to accurately predict the amounts of substances consumed and produced in any given chemical reaction.

Sodium Reactions

Sodium, a highly reactive metal, is known for its vigorous reactions, especially with water and alcohols such as methanol. These reactions release hydrogen gas, which is highly flammable. When sodium interacts with water, for example:For the reaction of sodium with water:

• The balanced equation is: \[ 2 \, \text{Na} + 2 \, \text{H}_2\text{O} \rightarrow 2 \, \text{NaOH} + \text{H}_2 \, \uparrow \]
• Sodium hydroxide (NaOH) and hydrogen gas (\( \text{H}_2 \)) are formed.
• This reaction is exothermic, meaning it releases heat.

When sodium interacts with methanol, a similar process occurs:

• Sodium exchanges places with the hydrogen in methanol, creating sodium methoxide (\( \text{CH}_3\text{ONa} \)) and hydrogen gas.
• The balanced equation is: \[ 2 \, \text{Na} + 2 \, \text{CH}_3\text{OH} \rightarrow 2 \, \text{CH}_3\text{ONa} + \text{H}_2 \, \uparrow \]

These reactions showcase sodium's reactivity with different substances, which is important in many industrial processes.

Sodium Hydride Reactions

Sodium hydride (NaH) is an ionic compound, where sodium donates an electron to hydrogen. It's less reactive than metallic sodium but still capable of vigorous reactions, especially with water and alcohols.For sodium hydride reacting with water:

• The balanced chemical equation is: \[ \text{NaH} + \text{H}_2\text{O} \rightarrow \text{NaOH} + \text{H}_2 \, \uparrow \]
• Sodium hydroxide and hydrogen gas are produced, similar to the reaction of metallic sodium with water.
• The reaction releases hydrogen gas, which may require safety precautions due to its flammability.

In the case of sodium hydride reacting with ethanol:

• Sodium hydride reacts with ethanol to form sodium ethoxide (\( \text{C}_2\text{H}_5\text{ONa} \)) and hydrogen gas.
• Balanced equation: \[ \text{NaH} + \text{C}_2\text{H}_5\text{OH} \rightarrow \text{C}_2\text{H}_5\text{ONa} + \text{H}_2 \, \uparrow \]

These reactions are particularly useful in laboratory settings, where sodium hydride can act as a strong base or reducing agent.