Synthetic Inorganic Chemistry

APPENDIX 353

TENSION OF SATURATED AQUEOUS VAPOR

Temp.

0°

5

10

15

16

17

18

19

20

Pressure

4.6 mm.

6.5

9.2

12.7

13.5

14.4

15.4

16.3

17.4

Temp.

21°

22

23

24

25

26

27

28

29

Pressure

18.5 mm.

19.7

20.9

22.2

23.6

25.1

26.5

28.1

29.8

Temp.

30°

35

40

50

60

70

80

90

100

Pressure

31.5 mm.

41.9

55.0

92.2

149.2

233.8

355.5

526.0

760.0

ELECTROMOTIVE SERIES
When a metal is in contact with a solution containing its ions,
a difference in electrical potential arises due to the resultant effect
of two tendencies: of the metal on the one hand to throw off posi-
tive ions and thus charge the solution positively, and of the metal
ions on the other hand to deposit on the metal and impart their
charges to it.
The figures given in the table are for the potential of a solution,
normal in the ions of the given metal, measured against the metal
itself which dips in the solution. The potential of a normal
solution of hydrogen ions measured against a hydrogen electrode
(platinum electrode saturated with hydrogen gas under atmos-
pheric pressure) is taken as zero, and the other potentials are
measured from this arbitrary zero point.
The elements for which no figures are given are placed in ap-
proximately their correct position in the series.

K +2.9
Na + 2.7
Ba + 2.7
Ca +2.7
Mg + 1.8
Al + 1.3
Mn + 1.1
Zn + 0.8
Cr +0.5

METALS

Fe(Fe++) +0.44

Cd +0.40

Co +0.23

Ni +0.23

Sn(Sn++) + 0.13

Pb +0.12

H 2 +0.00

Cu(Cu++) -0.34

NON-METALS

As —

Bi —

Sb —

Hg(Hg+) -0.74

Ag -0.80

pa —

Pt —

Au ,. -1.3

2
Cli
O 2 (in 1 N H+ solution).
Br 2

— I 2 -0.53

-1.36 O 2 (in IN OH" solution)... -0.40

-1.24 S —

-1.08