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Chapter 4: Problem 149

Phosphoric acid \(\left(\mathrm{H}_{3} \mathrm{PO}_{4}\right)\) is an important industrial chemical used in fertilizers, in detergents, and in the food industry. It is produced by two different methods. In the electric furnace method, elemental phosphorus \(\left(\mathrm{P}_{4}\right)\) is burned in air to form \(\mathrm{P}_{4} \mathrm{O}_{10},\) which is then reacted with water to give \(\mathrm{H}_{3} \mathrm{PO}_{4} .\) In the wet process, the mineral phosphate rock fluorapatite \(\left[\mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3} \mathrm{~F}\right]\) is reacted with sulfuric acid to give \(\mathrm{H}_{3} \mathrm{PO}_{4}\) (and \(\mathrm{HF}\) and \(\mathrm{CaSO}_{4}\) ). Write equations for these processes and classify each step as precipitation, acid-base, or redox reaction.

Short Answer

Expert verified
The two methods for producing phosphoric acid are classified as follows: the Electric Furnace method involves an acid-base reaction, and the Wet Process involves both a precipitation reaction and an acid-base reaction.

Step by step solution

01

Formulation of the Electric Furnace method reaction

In the electric furnace method, elemental phosphorus \(\mathrm{P}_{4}\) is burned in air to form \(\mathrm{P}_{4} \mathrm{O}_{10},\) and then reacted with water to give \(\mathrm{H}_{3} \mathrm{PO}_{4} .\) The reaction can be written as follows:\begin{align*} \mathrm{P}_{4} + 5 \mathrm{O}_{2} &\rightarrow \mathrm{P}_{4} \mathrm{O}_{10} \ \mathrm{P}_{4} \mathrm{O}_{10} + 6 \mathrm{H}_{2}\mathrm{O} &\rightarrow 4 \mathrm{H}_{3} \mathrm{PO}_{4}\end{align*}
02

Classify reaction of Electric Furnace method

Looking at the chemical reactions, since the oxidation states of all involved atoms do not change, these reactions are not redox reactions. Also, no solid forms that would precipitate out. So, these are not precipitate reactions. However, we see a base (water) and an acidic oxide (phosphoric oxide), which react to form acid (phosphoric acid). Therefore, these reactions are acid-base reactions.
03

Formulation of the Wet process reaction

In the wet process, the mineral phosphate rock fluorapatite \(\left[\mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3} \mathrm{~F}\right]\) is reacted with sulfuric acid to give \(\mathrm{H}_{3} \mathrm{PO}_{4},\) \(\mathrm{HF}\) and \(\mathrm{CaSO}_{4} .\) The reaction can be written as follows:\[\left[\mathrm{Ca}_{5}\left(\mathrm{PO}_{4}\right)_{3} \mathrm{~F}\right] + 5 \mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow 3 \mathrm{H}_{3} \mathrm{PO}_{4} + 5 \mathrm{CaSO}_{4} + \mathrm{HF}\]
04

Classify reaction of Wet Process

Looking at the chemical reaction, since the oxidation states of all involved atoms do not change, this reaction is not a redox reaction. However, a solid forms (calcium sulfate)—this is a precipitation reaction. Also, there is a reaction between a base (fluorapatite) and acid (Sulfuric acid) to form another acid (Phosphoric acid) and salt (Calcium sulfate). Therefore, this reaction is also an acid-base reaction.

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Most popular questions from this chapter

Which of the following are redox processes? (a) \(\mathrm{CO}_{2} \longrightarrow \mathrm{CO}_{3}^{2-}\) (b) \(\mathrm{VO}_{3} \longrightarrow \mathrm{VO}_{2}\) (c) \(\mathrm{SO}_{3} \longrightarrow \mathrm{SO}_{4}^{2-}\) (d) \(\mathrm{NO}_{2}^{-} \longrightarrow \mathrm{NO}_{3}^{-}\) (e) \(\mathrm{Cr}^{3+} \longrightarrow \mathrm{CrO}_{4}^{2-}\)

Nitric acid is a strong oxidizing agent. State which of the following species is least likely to be produced when nitric acid reacts with a strong reducing agent such as zinc metal, and explain why: \(\mathrm{N}_{2} \mathrm{O}\) \(\mathrm{NO}, \mathrm{NO}_{2}, \mathrm{~N}_{2} \mathrm{O}_{4}, \mathrm{~N}_{2} \mathrm{O}_{5}, \mathrm{NH}_{4}^{+}\).

Describe how you would prepare \(250 \mathrm{~mL}\) of a \(0.707 M \mathrm{NaNO}_{3}\) solution.

A useful application of oxalic acid is the removal of rust \(\left(\mathrm{Fe}_{2} \mathrm{O}_{3}\right)\) from, say, bathtub rings according to the reaction \(\begin{aligned} \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+& 6 \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(a q) \longrightarrow \\ & 2 \mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}^{3-}(a q)+3 \mathrm{H}_{2} \mathrm{O}+6 \mathrm{H}^{+}(a q) \end{aligned}\) Calculate the number of grams of rust that can be removed by \(5.00 \times 10^{2} \mathrm{~mL}\) of a \(0.100 \mathrm{M}\) solution of oxalic acid.

Hydrogen halides (HF, HCl, HBr, HI) are highly reactive compounds that have many industrial and laboratory uses. (a) In the laboratory, HF and \(\mathrm{HCl}\) can be generated by reacting \(\mathrm{CaF}_{2}\) and \(\mathrm{NaCl}\) with concentrated sulfuric acid. Write appropriate equations for the reactions. (Hint: These are not redox reactions.) (b) Why is it that HBr and HI cannot be prepared similarly-that is, by reacting NaBr and NaI with concentrated sulfuric acid? (Hint: \(\mathrm{H}_{2} \mathrm{SO}_{4}\) is a stronger oxidizing agent than both \(\mathrm{Br}_{2}\) and \(\mathrm{I}_{2} .\) ) (c) HBr can be prepared by reacting phosphorus tribromide \(\left(\mathrm{PBr}_{3}\right)\) with water. Write an equation for this reaction.
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