Question

The pair of compounds which cannot exist together is: (a) \(\mathrm{NaHCO}_{3} \& \mathrm{NaOH}\) (b) \(\mathrm{Na}_{2} \mathrm{CO}_{3} \& \mathrm{NaHCO}_{3}\) (c) \(\mathrm{Na}_{2} \mathrm{CO}_{3} \& \mathrm{NaOH}\) (d) \(\mathrm{NaHCO}_{3} \& \mathrm{NaCl}\)

Short answer

The pair of compounds \(\mathrm{NaHCO}_{3} \& \mathrm{NaOH}\) cannot coexist.

Step-by-step solution

Understanding Compound Interaction

We are asked to identify a pair of compounds that cannot coexist due to a chemical reaction between them. One way to deduce this is by evaluating chemical reactions involving acid-base interactions or any possible decomposition or precipitation.

Pair (a) Analysis: \(\mathrm{NaHCO}_{3} \& \mathrm{NaOH}\)

Sodium bicarbonate (\(\mathrm{NaHCO}_3\)) can react with sodium hydroxide (\(\mathrm{NaOH}\)) in an acid-base neutralization reaction to form sodium carbonate (\(\mathrm{Na}_2\mathrm{CO}_3\)), water, and carbon dioxide: \[ \mathrm{NaOH} + \mathrm{NaHCO}_3 \rightarrow \mathrm{Na}_2\mathrm{CO}_3 + \mathrm{H}_2\mathrm{O} + \mathrm{CO}_2 \] Hence, these compounds react and cannot coexist.

Pair (b) Analysis: \(\mathrm{Na}_{2} \mathrm{CO}_{3} \& \mathrm{NaHCO}_{3}\)

\(\mathrm{Na}_2\mathrm{CO}_3\) and \(\mathrm{NaHCO}_3\) do not chemically react with each other, as \(\mathrm{NaHCO}_3\) can be formed from \(\mathrm{Na}_2\mathrm{CO}_3\) when dissolved in water, without any additional reaction under normal conditions.

Pair (c) Analysis: \(\mathrm{Na}_{2} \mathrm{CO}_{3} \& \mathrm{NaOH}\)

Sodium carbonate (\(\mathrm{Na}_2\mathrm{CO}_3\)) and sodium hydroxide (\(\mathrm{NaOH}\)) are both basic, and no reaction occurs between the two compounds. They can coexist in solution.

Pair (d) Analysis: \(\mathrm{NaHCO}_{3} \& \mathrm{NaCl}\)

\(\mathrm{NaHCO}_3\) and \(\mathrm{NaCl}\) do not react in an aqueous solution under normal conditions since \(\mathrm{NaCl}\) is a neutral salt and does not affect the bicarbonate ion in \(\mathrm{NaHCO}_3\) significantly.

Identify Non-coexisting Pair

Based on the analyses, the pair \(\mathrm{NaHCO}_{3} \& \mathrm{NaOH}\) undergoes a chemical reaction and cannot exist together, making option (a) the correct answer.

Key concepts

Acid-Base Reactions

Acid-base reactions are chemical processes where an acid and a base interact to form products, typically salt and water. These reactions are fundamental to many chemical processes in biology, industry, and chemistry. For instance, in our exercise, sodium bicarbonate \( (\mathrm{NaHCO}_3) \), which acts like a weak acid, reacts with sodium hydroxide \( (\mathrm{NaOH}) \), a strong base, in an acid-base reaction yielding sodium carbonate \((\mathrm{Na}_2\mathrm{CO}_3)\), water \((\mathrm{H}_2\mathrm{O})\), and carbon dioxide \((\mathrm{CO}_2)\):

• Acid: \(\mathrm{NaHCO}_3\) provides \(\mathrm{H}^+\) ions.
• Base: \(\mathrm{NaOH}\) provides \(\mathrm{OH}^-\) ions.
• Resulting products: \(\mathrm{Na}_2\mathrm{CO}_3\), \(\mathrm{H}_2\mathrm{O}\), and \(\mathrm{CO}_2\).

The acid-base interactions are crucial since they govern crucial principles like the pH level of solutions and the chemical form that compounds will take in different environments. By understanding these reactions, we can predict how substances will behave in varying conditions.

Compound Coexistence

Compound coexistence refers to the ability of different substances to exist together in a solution without undergoing a chemical change. The interaction of compounds in a mixture is determined by their chemical properties, which dictate whether or not they will react with one another. For example, in our exercise:

• \(\mathrm{Na}_2\mathrm{CO}_3\) and \(\mathrm{NaHCO}_3\): Both are stable together in a solution since no reaction occurs naturally under typical conditions.
• \(\mathrm{NaHCO}_3\) and \(\mathrm{NaCl}\): These compounds do not react as \(\mathrm{NaCl}\) is a neutral salt, not interfering with the bicarbonate within \(\mathrm{NaHCO}_3\).

Recognizing which compounds can coexist without reacting helps in understanding reaction dynamics and solution stability, laying a foundation for more complex chemistry applications. Avoiding unwanted reactions is crucial in processes such as formulating buffers, pharmaceuticals, and even culinary applications.

Chemical Reaction Analysis

Chemical reaction analysis involves reviewing the potential reactions between compounds to determine the outcomes and identify possible reactions. This practice is essential in predicting what compounds can be mixed safely without inducing a chemical transformation, which is critical in fields like chemical engineering and environmental science.

• Step-by-step analysis helps to establish which compounds can coexist, as highlighted in the exercise discussion.
• The evaluation often includes considering the reactivity, ion exchange, and thermodynamics involved in the potential chemical interaction.

For our example, the step-by-step process allowed identifying that \(\mathrm{NaHCO}_3\) and \(\mathrm{NaOH}\) react together due to an acid-base reaction, thus cannot coexist without interaction. Understanding such interactions allows chemists and students to manipulate conditions effectively for desired reactions to occur or be avoided.