Problem 48 - Chemistry The Central Science In Si Units

Question

Write a balanced equation for each of the following reactions. (You may have to guess at one or more of the reaction products, but you should be able to make a reasonable guess, based on your study of this chapter.) (a) Hydrogen selenide can be prepared by reaction of an aqueous acid solution on aluminum selenide. \((\mathbf{b})\) Sodium thiosulfate is used to remove excess \(\mathrm{Cl}_{2}\) from chlorine-bleached fabrics. The thiosulfate ion forms \(\mathrm{SO}_{4}^{2-}\) and elemental sulfur, while \(\mathrm{Cl}_{2}\) is reduced to \(\mathrm{Cl}^{-}\).

Step-by-Step Solution

Answer

(a) \( \text{Al}_2\text{Se}_3 + 6\text{H}_2\text{O} \rightarrow 3\text{H}_2\text{Se} + 2\text{Al(OH)}_3 \); (b) \( 2\text{Na}_2\text{S}_2\text{O}_3 + \text{Cl}_2 \rightarrow 2\text{Na}_2\text{SO}_4 + \text{S}_2 + 2\text{NaCl} \).

Step 1: Identify reactants and products for reaction (a)

The reaction involves aluminum selenide (Al2Se3) reacting with an aqueous acid to produce hydrogen selenide (H2Se). The likely reaction involves water (H2O) providing hydrogen ions (H+) in a similar way as when acids react with metal salts.

Step 2: Write preliminary unbalanced equation for reaction (a)

Start by writing the unbalanced chemical equation: \[ \text{Al}_2\text{Se}_3 + 6\text{H}_2\text{O} \rightarrow 3\text{H}_2\text{Se} + 2\text{Al(OH)}_3 \] Here, aluminum ions react with hydroxide ions from water, forming aluminum hydroxide as a product.

Step 3: Balance the equation for reaction (a)

To balance the equation, ensure equal numbers of each atom on both sides:- Balance aluminum by ensuring there are 2 moles of Al on each side.- Balance selenium by ensuring there are 3 moles of Se on each side.- Ensure hydrogen and oxygen are balanced with the number of water molecules already accounted for with Al(OH)₃.The balanced equation is: \[ \text{Al}_2\text{Se}_3 + 6\text{H}_2\text{O} \rightarrow 3\text{H}_2\text{Se} + 2\text{Al(OH)}_3 \]

Step 4: Identify reactants and products for reaction (b)

In reaction (b), sodium thiosulfate (Na2S2O3) reacts with chlorine gas (Cl2). Sodium thiosulfate is converted to sulfate ions (SO4²⁻) and elemental sulfur (S), while Cl2 is reduced to chloride ions (Cl⁻).

Step 5: Write preliminary unbalanced equation for reaction (b)

Formulate the reaction as follows: \[ \text{Na}_2\text{S}_2\text{O}_3 + \text{Cl}_2 \rightarrow \text{Na}_2\text{SO}_4 + \text{S} + \text{NaCl} \] Elemental sulfur (S) and sodium sulfate (Na2SO4) are produced.

Step 6: Balance the equation for reaction (b)

Balance each element across the equation to balance the chemical reaction:- Balance sulfur and chlorine by ensuring 2 moles of thiosulfate yield 1 mole of sulfur and sufficient amounts of sulfur in sodium sulfate.- Balance sodium and chloride as needed.The balanced equation reads: \[ 2\text{Na}_2\text{S}_2\text{O}_3 + \text{Cl}_2 \rightarrow \text{2Na}_2\text{SO}_4 + \text{S}_2 + 2\text{NaCl} \]

Key Concepts

Balanced Chemical Equations

Balancing chemical equations is essential for accurately representing chemical reactions. An unbalanced equation can depict the reactants and products but does not show the conservation of mass. To balance a chemical equation, begin by writing down the unbalanced equation. This step identifies the reactants and products involved.
Next, check for each type of atom and ensure the equation has the same number of each atom on both sides. This often involves counting and comparing. Use coefficients to adjust the number of molecules or compounds.

• Balancing involves adjusting coefficients, not changing the chemical formula of the substances involved.
• Every balanced equation respects the law of conservation of mass.
• Each side of the equation should reflect the same total mass to ensure atoms are neither created nor destroyed.

By following these steps, you maintain the chemical identity and stoichiometric balance required for accurate predictions and understanding of the reactions.

Reaction Products

Understanding reaction products is crucial for predicting the outcome of a chemical reaction. Products are the substances formed from the reactants in a chemical reaction. A reaction may yield one or multiple products depending on the reactants and the reaction conditions.
For example, in reaction (a) from the original exercise, the products are hydrogen selenide ( H₂Se) and aluminum hydroxide ( Al(OH)₃). By identifying these, you can predict the type of reaction and its possible uses or implications.

• Reactions not only transform the substances but also involve energy changes.
• Knowing the reaction products allows for the prediction of reaction behavior and potential applications.
• The formation of by-products should always be considered, as they can impact the efficiency and safety of chemical processes.

This understanding equips you with the ability to derive reaction equations and anticipate industrial and lab-scale outcomes.

Sodium Thiosulfate Reactions

Sodium thiosulfate is a fascinating compound often used in various practical applications, including as a dechlorinator in chlorine-bleached fabrics. Understanding its reactions helps grasp their chemical implications and importance.
In exercise (b), sodium thiosulfate ( Na₂S₂O₃) reacts with chlorine ( Cl₂), leading to its conversion into sulfate ions ( SO₄²⁻) and elemental sulfur ( S) while reducing chlorine to chloride ions ( Cl⁻).

• Sodium thiosulfate works by providing sulfur atoms that react with chlorine to neutralize it.
• The reaction with sodium thiosulfate displays typical redox behavior, characterized by electron transfer.
• This reaction is not only integral in neutralizing chlorine but also showcases the versatility of thiosulfates in chemistry.

Through these reactions, sodium thiosulfate proves just how diverse and significant a role chemical agents can play in materials processing and environmental chemistry.