22.3.2 Phosphorus

Question 1

Phosphorus

Answer 1

• Phosphorus exists mostly as phosphate in rock.
• Phosphorus reacts with halogens to form several different compounds.
• Oxides of phosphorus react with water to form acids.
• Arsenic, antimony, and bismuth are the other three group 15 elements.

Question 2

note 1

Answer 2

• Phosphorus exists mostly as phosphate in rock. To form
  elemental phosphorus, phosphate salts (such as calcium
  phosphate) are reduced with silicon dioxide and carbon. The product of this reaction is white phosphorus (P 4 ).
• The 60° bond angles of white phosphorus are relatively
  unstable. Therefore, white phosphorus reacts violently with oxygen in air. White phosphorus can be converted to red phosphorus or black phosphorus by heating in the absence of air. White, red, and black phosphorus are allotropes of phosphorus.
• Phosphorus reacts with chlorine to form liquid phosphorus trichloride (PCl 3 ). If there is an excess of chlorine, solid phosphorus pentachloride (PCl 5 ) can form.
• Phosphorus reacts with fluorine to form solid phosphorus pentafluoride (PF 5 ).
• Hydroiodic acid (HI) is formed commercially by the
  hydrolysis of phosphorus triiodide (PI 3 ). Phosphorous acid (H 3 PO 3 ) is also formed in this reaction. Similarly, the hydrolysis of phosphorus pentiodide (PI 5 ) produces
  phosphoric acid (H 3 PO 4 ) in addition to hydroiodic acid (HI).
• Oxides of phosphorus react with water to form acids.
  Tetraphosphorus decoxide (P 4 O 10 ) reacts with water to form phosphoric acid (H 3 PO 4 ), while tetraphosphorus hexoxide (P 4 O 6 ) reacts with water to form phosphorous acid (H 3 PO 3 ).
• Strike anywhere matches use reactions of phosphorus
  compounds. The reaction of tetraphosphorus trisulfide (P 4 S 3 ) with potassium chlorite (KClO 3 ) and oxygen is very exothermic, and lights the match.

Question 3

note 2

Answer 3

• Phosphoric acid molecules can condense in water. The
  monomer (H 3 PO 4 ) is sometimes referred to as orthophosphoric acid, while the dimer (H 4 P 2 O 7 ) is called pyrophosphoric acid. Metaphosphoric acid is a polymer of phosphoric acid made from the condensation of many phosphoric acid molecules. In nature, organisms carry out a similar reaction, forming adenosine triphosphate (ATP). ATP acts as an energy currency in cells—breaking the phosphate bonds releases energy.
• Soaps become protonated at low pH, which reduces their effectiveness. Phosphate anions can be used in soaps as builders, which make the solution slightly more alkaline. However, phosphates cause algal blooms when they get into the water supply. Therefore, carbonates are now used, rather than phosphates.
• Arsenic, antimony, and bismuth are the other three group 15 elements.
• Arsenic (As) is used in gallium arsenide semiconductors. Gallium arsenide can also emit light, and is used in light emitting diodes (LEDs).
• Antimony (Sb) and bismuth (Bi) are components of pewter. Pewter was used extensively in the sixteenth and seventeenth centuries for household serving items.

Question 4

Which of the following applications of group 15 elements is not correctly matched to the appropriate element(s)?

Answer 4

light-emitting diode / bismuth

Question 5

Which of the following Group 15 (VA) elements is NEVER found uncombined in nature?

Answer 5

P

Question 6

Which of the reactions of phosphorus compounds below represents that of an unbalanced equation?

Answer 6

P4S3 + KClO3 + O2 → P4O10 + SO2 + KCl

Question 7

The formation and breaking of P–O bonds is used as energy currency in which of the following biological molecules?

Answer 7

ATP

Question 8

Many laundry detergents are labeled as being “phosphate free.” If phosphorus compounds such as TSP make good “builders”, why would these chemicals be removed from consumer products such as detergents?

Answer 8

They can cause algal blooms, rapidly depleting water of O2.

Question 9

Phosphorus is most commonly found in nature as:

Answer 9

Phosphate rock

Question 10

Which compound contains phosphorus in the +3 oxidation state?

Answer 10

H3PO3

Question 11

Which of the following best describes the role of trisodium phosphate (“TSP”) as an ingredient in laundry or dishwashing detergent?

Answer 11

Controls pH and precipitates calcium and magnesium ions out of solution

Question 12

Which of these phosphorus compounds is mismatched with its name?

Answer 12

C: Tripolyphosphoric acid

Question 13

Which of the following categories of phosphorus compounds contains a mistake?

Answer 13

phosphorus halides: PF3, PCl3, PBr3, PBr4, PCl5