Introduction to Hydrogen Peroxide/Physical and Chemical Properties

NOTE: Care must be taken to ensure that the sample holder or prism is non-catalytic to H₂O₂ lest the oxygen bubbles formed through decomposition interfere with the measurements.

The refractive index for H₂O₂ is greater than that of water, and the curve relating to composition is slightly concave upward.

H₂O₂ Conc.	h _D
wt.%	25^oC	20^oC

0.0₀ 10.1₀ 19.9₈ 30.1₁ 40.0₃ 50.1₀	1.3325₁ 1.3388₁ 1.3452₁ 1.3520₃ 1.3588₅ 1.3661₁	1.3329₉ 1.3394₆ 1.3460₃ 1.3529₆ 1.3598₆ 1.3672₄

H₂O₂ Conc.	h _D
wt.%	25^oC	20^oC

60.6₆ 70.1₅ 79.8₆ 92.3₆ 96.2₆ 99.3₀	1.3738₉ 1.3815₁ 1.3892₇ 1.3999₈ 1.4033₃ 1.4060₇	1.3750₈ 1.3828₄ 1.3907₂ 1.4015₇ 1.4049₅ 1.4077₄

The temperature coefficient for the refractive index is also greater for H₂O₂ than it is for water:

Temp.	Approximate Concentration, wt.%
^oC	10	20	30	40	50	60	70	80	90	100

20 21 22 23 24	0.9 0.8 0.6 0.4 0.2	1.2 1.9 0.7 0.4 0.2	1.3 1.0 0.8 0.5 0.3	1.4 1.1 0.9 0.6 0.3	1.4 1.1 0.9 0.6 0.3	1.5 1.2 1.0 0.6 0.3	1.6 1.2 1.0 0.6 0.3	1.7 1.3 1.0 0.7 0.4	1.8 1.4 1.1 0.7 0.4	1.9 1.5 1.1 0.8 0.4

.			H₂O₂	Water
Specific refraction	r_D	cc/g, 25 ^oC	0.1705	0.2060
Molar refraction	[R]_D	cc/mole, 25 ^oC	5.801	3.712
Polarizability	a x 10²⁴	cc/molecule, 25 ^oC	2.30	1.47
Molar dispersion	[R]_G – [R]_c	cc/mole, 20 ^oC	1.3576	0.9285
Dispersion constant	a x 10^-30	sec^-2, 20 ^oC	8.479	6.532
Characteristic frequency	n ₀ x 10^-15	sec^-1, 20 ^oC	2.979	2.94

Ref: P.A. Giguere, Can. J. Res. 21B:156 (1943)
P.A. Giguere and P.Geoffrion, Can. J. Res., 27B:168 (1949)

H₂O₂ and its solutions are not optically active and there is no rotation of the plane of polarization on passing light through them. When placed in a magnetic field, however, rotation of the plane does occur – termed the Faraday effect, or magneto-optic rotation. This is described by the equation:

H₂O₂ Conc.	Refractive	Verdet Constant, V, min/gauss cm x 10³
wt.%	Index, h	5893	5780	5461	4358

0.0 18.1 38.1 50.9 62.0 78.5 96.0 100.0	1.3330 1.3447 1.3585 1.3680 1.3766 1.3899 1.4052 1.4112	13.09 12.91 12.69 12.53 12.30 11.98 11.60 11.48	13.64 13.38 13.15 12.98 12.80 12.45 12.03 11.90	15.40 15.13 14.86 14.60 14.43 14.07 13.64 13.32	25.21 25.00 24.47 24.22 24.11 23.45 22.70 22.65

Line	Frequency Mc/sec	Remarks

1	14,829.5 ą 0.2	quadratic Stark effect J ^* = 1
2	37,517.6 ą 0.2	quadratic Stark effect J ^* = 2
3	22,054.5 ą 0.2	quadratic Stark effect J ^*_min = 7, \|DJ\| = 1
4	27,639.6 ą 0.2	quadratic Stark effect J ^*_min = 7, \|DJ\| = 1
5	11,072.4 ą 0.5	quadratic Stark effect probably high J
6	35,916 ą 2	quadratic Stark effect high J, \|DJ\| = 1
7	39,0333 ą 2	probably high J
8	39,495 ą 2	probably high J
9	39,790 ą 2	probably high J

All lines are of medium or strong intensity, except 5, 6 and 7, which are relatively weak.

Ref: J.T. Massey and D.R. Bianco, Physical Rev., 85:717 (1952); J. Chem. Phys., 22:442 (1954)

Absorption of infrared radiation by H₂O₂ is relatively weak. For reference, the principal absorption bands for water are: 0.85, 0.98, 1.18, 1.46, 1.98, 2.97, and 6.1 m .

Wavelength m	Wave Number cm^-1	Intensity	Temp, ^oC

18.2 15.8 11.4 7.4 4.85 4.4 3.6 3.6 3.48 2.93 2.3 2.1 1.6 1.5 1.5 1.2 1.01 0.77	550 635 880 1350 2000 2300 2780 2796 2864 3418 4290 4720 6100 6700 6805 8040 9900 13000	very weak medium weak medium very weak very weak medium medium medium strong very weak very weak very weak weak very weak very weak weak weak	-- -30 -- -- -- -- -- -- -- -- 20 -- 20 -- 20 20 -- 12, 55

If a substance is illuminated with monochromatic light, the radiation scattered by the substance is composed not only of the exciting wavelength, but also one or more other wavelengths independent of the exciting wavelength. The spectrum of these scattered wavelengths is termed the Raman spectrum, which is in effect the opposite of an absorption spectrum.

For practical purposes, H₂O₂ solutions are transparent for radiation to which the eye is sensitive (i.e., between 4000 and 8000 Angstroms). In bulk solutions, however, H₂O₂ will appear slight pale blue with a nuance of green. The yellow to green tint is attributed to light scattering of entrained bubbles; whereas the blue note is similar to that seen in water.

Wavelength (Angstroms)	Molecular extinction coefficient e, liters/mole.cm

4000 3800 3600 3400 3200 3000 2800 2600 2537 2400 2200 2000	0.00066 0.0022 0.010 0.047 0.22 1.0 4.2 13 19.6 ą 0.3 35 76 140

NOTES:

1. The absorption coefficient for both liquid and vapor H₂O₂ is essentially the same.
2. The shape of the curve relating the extinction coefficient to the wavelength is slightly parabolic.

3. The absorption of ultraviolet radiation by H₂O₂ results in dissociation of the molecule into two hydroxyl radicals (HO^.), although other reactions are possible and may occur to some extent.

4. Beer’s law is not strictly obeyed by H₂O₂ solutions, as higher concentrations of H₂O₂ absorb to a greater extent than Beer’s law would predict (i.e., the molecular extinction coefficient decreases as H₂O₂ concentration increases > 50% wt.%).

5. The presence of alkali shifts the absorption curve toward the visible (i.e., increases the absorption coefficient). This is due to the dissociation of H₂O₂ into the perhydroxyl ion (HO₂^-) that absorbs more intensely than H₂O₂.