Chapter 8. Phosphorus
Answers to  Questions

1. 15.91 M

2.

P4 + O2(g)  P4O6 or P4O10 depending on the amount of O2

P4O10(s) + H2O(l) 4 H3PO4

PBr3 + Br2 PBr5

CH3CH2OH + P4S10 4 (CH3CH2O)2PSSH + H2S

K(s) + P4(s)  4 K3P

CH3CH2CH2Li + PCl3 P(CH2CH2CH3)3

CH3COOH + PCl3 CH3COCl + H3PO3


3.

PCl3 + D2O(s)  D3PO3 + 3 DCl
or
PCl3(s) + Cl2(s)  PCl5

PCl5 + D2O(s)  D3PO4+ 5 DCl


4.

P4O10 + 4 HNO3(s)  2 N2O5+ 4 HPO3
5.
8 P4 + 7 S8(s)  8 P4S7  (and other similar reactions!)


6.

orthophosphoric acid H3PO4

metaphosphoric acid HPO3

pyrophosphoric acid H4P2O7

sodium tripolyphosphate Na5P3O10

hydroxyapatite Ca10(OH)2(PO4)6

calcium phosphate Ca3(PO4)2

calcium dihydrogen phosphate Ca(H2PO4)2

calcium phosphide Ca3P2


7. This is the procedure:

two H3PO4 minus one H2O = H4P2O7

three H3PO4 minus two H2O = H5P3O10

four H3PO4 minus three H2O = H6P4O13

five H3PO4 minus four H2O = H7P5O16


8. The curves on the plot would not be as prominent.  The individual curves would intercept each other at the same pH values, however.

9. not balanced:

P4S3(s) + KClO3(s)  P4O6(s) + SO2(g) + KCl(s)
or
P4S3(s) + KClO3(s)  P4O10(s) + SO2(g) + KCl(s)


10.

(a) Ca3P4(s) + 6 H2O(l)  2 PH3(g) + 3 Ca(OH)2(s)

(b) 4 PH3(g) + 8 O2(g)  P4O10(s) + 6 H2O(l)

11.
SCa3(PO4)2 = 1.64 x 10-7 mol/L

Ksp = (3S)3(2S)2 = 108 S5 = 1.3 x 10-32

12. In P4, the theoretical tetrahedral angle (109o) is reduced to 60o angles.  This causes considerable stress which leads to a much more reactive species.

13. The triple point temperature must be above 417 oC and at a pressure greater than 1 atm.

14. N=N double bond is expected to be stronger than the P=P double bond.

15. 2.5%
 

16. PCl4+ is AB4, tetrahedral and PCl6- is AB6, octahedral

17.

(a) 21.4 %N
(b) 23.7 %P
(c) 54.2 %P