APPENDIX 363
holds them together. The formulas of methane, carbon tetra-
chloride, sulphate ion, perchlorate ion, are shown as follows, it
being remembered that the kernel charges are: 1 for hydrogen,
4 for carbon, 6 for oxygen, and 7 for chlorine; and that the
completed sheath of hydrogen contains but two electrons.
H:
H
C:
H
H : Cl:
Cl:
C :
Cl:
Cl:
*
: 0:
.
0:
S :
0 :
0:
*
: 0:
0 :
Cl:
0 :
0:
If one counts the positive and negative charges of these formulas it
is noted that CH 4 and CC1 4 are electrically neutral, but that the
sulphate ion has a net of 2 negative charges, S0 4 ~~, and the
perchlorate ion has a net of one negative charge, C104~.
SOLUBILITIES
A substance is classified as soluble if as much as 2 parts by
weight dissolves in 100 parts of water. There is no sharp dividing
line between soluble and insoluble, but in general a substance is
classified as insoluble if less than 1 part by weight dissolves in 100
parts of water. It is advisable to learn the following general
statements of solubilities.
SOLUBLE IN WATER
- All simple salts of sodium, potassium, and ammonium.
- Acetates and nitrates, except some basic acetates and ni-
trates.
- Chlorides, except AgCl, HgCl, CuCl, PbCl 2.
- Sulphates, except BaSO 4 , SrSO 4 , CaSO 4 , PbSO 4.
INSOLUBLE IN WATER
- Oxides and hydroxides
- Carbonates
- Phosphates
- Sulphides and ammonium.
except those of
sodium, potassium,
