Problem 94 - General Chemistry: Principles and Modern Applications

Question

Write chemical equations to represent the following reactions. (a) Calcium phosphate is heated with silicon dioxide and carbon, producing calcium silicate \(\left(\mathrm{CaSiO}_{3}\right)\) phosphorus ( \(\mathrm{P}_{4}\) ), and carbon monoxide. The phosphorus and chlorine react to form phosphorus trichloride, and the phosphorus trichloride and water react to form phosphorous acid. (b) Copper metal reacts with gaseous oxygen, carbon dioxide, and water to form green basic copper carbonate, \(\mathrm{Cu}_{2}(\mathrm{OH})_{2} \mathrm{CO}_{3}\) (a reaction responsible for the formation of the green patina, or coating, often seen on outdoor bronze statues). (c) White phosphorus and oxygen gas react to form tetraphosphorus decoxide. The tetraphosphorus decoxide reacts with water to form an aqueous solution of phosphoric acid. (d) Calcium dihydrogen phosphate reacts with sodium hydrogen carbonate (bicarbonate), producing calcium phosphate, sodium hydrogen phosphate, carbon dioxide, and water (the principal reaction occurring when ordinary baking powder is added to cakes, bread, and biscuits).

Step-by-Step Solution

Answer

The chemical equations for the reactions discussed are represented as follows:\[(a)\, \text{Ca}_3(\text{PO}_4)_2 + \text{SiO}_2 + 3\text{C} \rightarrow \text{CaSiO}_3 + 2\text{P}_4 + 3\text{CO},\, \text{P}_4 + 6\text{Cl}_2 \rightarrow 4\text{PCl}_3,\, \text{PCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{H}_3\text{PO}_3 + 3\text{HCl}\] \[(b)\, 2\text{Cu}+ \text{O}_2 + \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{Cu}_2(\text{OH})_2\text{CO}_3\] \[(c)\, \text{P}_4+ 5\text{O}_2 \rightarrow \text{P}_4\text{O}_{10},\, \text{P}_4\text{O}_{10}+ 6\text{H}_2\text{O} \rightarrow 4\text{H}_3\text{PO}_4\] \[(d)\, \text{Ca(H}_2\text{PO}_4)_2 + 2\text{NaHCO}_3 \rightarrow \text{Ca}_3(\text{PO}_4)_2 + 2\text{NaH}_2\text{PO}_4 + 2\text{CO}_2 + 2\text{H}_2\text{O}\]

Step 1: Reaction of Calcium phosphate, Silicon dioxide, and Carbon

The chemical reaction can be written as: \[ \text{Ca}_3(\text{PO}_4)_2 + \text{SiO}_2 + 3\text{C} \rightarrow \text{CaSiO}_3 + 2\text{P}_4 + 3\text{CO} \] React the phosphorus with chlorine: \[ \text{P}_4 + 6\text{Cl}_2 \rightarrow 4\text{PCl}_3 \] React the phosphorus trichloride with water to form phosphorous acid and HCl: \[ \text{PCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{H}_3\text{PO}_3 + 3\text{HCl} \]

Step 2: Reaction of Copper, Oxygen, Carbon dioxide, and Water

The reaction can be described as: \[ 2\text{Cu}(s)+ \text{O}_2(g) + \text{CO}_2(g) + \text{H}_2\text{O}(l) \rightarrow \text{Cu}_2(\text{OH})_2\text{CO}_3(s) \] This is the reaction forming a green patina on bronze statues.

Step 3: Reaction of White phosphorus and Oxygen

The reaction can be described as: \[ \text{P}_4(s)+ 5\text{O}_2(g) \rightarrow \text{P}_4\text{O}_{10}(s) \] React the tetraphosphorus decoxide with water: \[ \text{P}_4\text{O}_{10}(s) + 6\text{H}_2\text{O}(l) \rightarrow 4\text{H}_3\text{PO}_4(aq) \] This forms an aqueous solution of phosphoric acid.

Step 4: Reaction of Calcium dihydrogen phosphate with Sodium bicarbonate

The chemical reaction can be described as: \[ \text{Ca(H}_2\text{PO}_4)_2(s) + 2\text{NaHCO}_3(s) \rightarrow \text{Ca}_3(\text{PO}_4)_2(s) + 2\text{NaH}_2\text{PO}_4(s) + 2\text{CO}_2(g) + 2\text{H}_2\text{O}(l) \] It's the principal reaction that occurs when baking powder is added to dough.

Key Concepts

Calcium Phosphate Reactions

Calcium phosphate, when heated with silicon dioxide (also known as silica) and carbon, undergoes a fascinating chemical transformation. The reaction produces calcium silicate, phosphorus in the form of tetraphosphorus, and carbon monoxide. This chemical equation can be represented as follows: \[ \text{Ca}_3(\text{PO}_4)_2 + \text{SiO}_2 + 3\text{C} \rightarrow \text{CaSiO}_3 + 2\text{P}_4 + 3\text{CO} \] In this process, phosphorus generated from the reaction can further react with chlorine gas to form phosphorus trichloride: \[ \text{P}_4 + 6\text{Cl}_2 \rightarrow 4\text{PCl}_3 \] When phosphorus trichloride reacts with water, it produces phosphorous acid and hydrochloric acid: \[ \text{PCl}_3 + 3\text{H}_2\text{O} \rightarrow \text{H}_3\text{PO}_3 + 3\text{HCl} \] These reactions highlight the complex interplay of elements and compounds in chemical processes.

Copper Patina Formation

Copper metal, renowned for its distinctive reddish-brown color, can react with oxygen, carbon dioxide, and water to form a green compound known as basic copper carbonate. This is the process that gives copper statues their characteristic green patina, often seen on structures such as the Statue of Liberty. The reaction is known as: \[ 2\text{Cu}(s) + \text{O}_2(g) + \text{CO}_2(g) + \text{H}_2\text{O}(l) \rightarrow \text{Cu}_2(\text{OH})_2\text{CO}_3(s) \] The resulting patina is not merely aesthetic; it also serves as a protective layer that safeguards the copper underneath from further corrosion. This transformation showcases how metals interact with environmental factors to undergo chemical changes.

Phosphorus Oxygen Reaction

White phosphorus is a highly reactive form of phosphorus known for its ability to glow in the dark and release smoke upon contact with air. When it combines with oxygen gas, it forms tetraphosphorus decoxide: \[ \text{P}_4(s) + 5\text{O}_2(g) \rightarrow \text{P}_4\text{O}_{10}(s) \] Subsequent interaction of tetraphosphorus decoxide with water results in the formation of phosphoric acid, a key ingredient in various industrial and consumer products: \[ \text{P}_4\text{O}_{10}(s) + 6\text{H}_2\text{O}(l) \rightarrow 4\text{H}_3\text{PO}_4(aq) \] These reactions exemplify how reactive phosphorus can transform into useful compounds, reflecting the dynamic nature of chemical behavior.

Baking Powder Chemical Reaction

Baking powder, a staple in kitchens around the world, plays a critical role in making baked goods rise. This is achieved through an intriguing reaction between calcium dihydrogen phosphate and sodium bicarbonate (more commonly known as baking soda). The reaction can be shown as: \[ \text{Ca(H}_2\text{PO}_4)_2(s) + 2\text{NaHCO}_3(s) \rightarrow \text{Ca}_3(\text{PO}_4)_2(s) + 2\text{NaH}_2\text{PO}_4(s) + 2\text{CO}_2(g) + 2\text{H}_2\text{O}(l) \] The carbon dioxide (\(\text{CO}_2\) gas produced causes the dough to expand, creating the light and airy texture of cakes, breads, and biscuits. This reaction demonstrates how a simple chemical process can significantly impact food texture and quality.