Name: aluminum hydroxide; aluminium hydroxide
CAS Number: 21645-51-2
Chemical Formula: Al(OH)3
Molar Mass: 78.003558 g
Mass Percent: Al 34.590 %; O 61.533 %; H 3.8765 % 


• inorganic


• "Aluminum hydroxide is an effective antacid because it is chemically, a base. As such, it reacts with stomach acid (hydrochloric acid; HCl), to reduce the symptoms of heartburn, upset stomach, acid indigestion, and gastritis, an inflammation of the stomach lining. The compound can also be used to treat peptic ulcers on a long-term basis. A peptic ulcer is an open sore in the lining of the stomach or the first part of the small intestine.
Aluminum hydroxide also has a number of industrial applications, such as:
• A raw material for the preparation of other aluminum compounds;
• An additive for cosmetics, paper, plastics, and rubber to give the final product more bulk;
• In abrasives designed for use with plastics and brass;
• An additive for glass products that adds strength and resistance to attack by chemicals and weathering and to heat shock;
• As the world's most popular flame retardant." 1

• "Hydrangea colors ultimately depend on the availability of aluminum ions (Al3+) within the soil...But in neutral to basic soil, the ions combine with hydroxide ions (OH-) to form immobile aluminum hydroxide, Al(OH)3. Consequently, for the bluing of hydrangea blooms, one needs both aluminum ions and acidic soil. The best soil aadditive for bluing is one that combines both, such as commercially available aluminum sulfate, Al2(SO4)3. Conversely, if one wishes to change blue blooming hydrangea to red-blooming, adding lime (calcium hydroxide, Ca(OH)2) results in basic soil and the desired color transition." 2

Physical Properties

Density (g/cm3):
2.42 at room temperature/pressure 3
* - 1 atm pressure


insoluble:  3
soluble:  3



ΔHf° (s): -307 kcal/mol 4 = -1,284.49 kJ/mol
S° (s): 17 cal/(mol•K) 5 = 71.13 J/(mol•K)
ΔGf° (s): -312.1 kcal/mol 6 = -1,305.83 kJ/mol


Safety Information

NFPA 704 Ratings:
Health: 1 - Exposure would cause irritation with only minor residual injury.
Flammability: 0 - Will not burn.
Reactivity: 0 - Normally stable, even under fire exposure conditions, and is not reactive with water.

For More Information


(1) - Schlager, Neil, Weisblatt, Jayne, Newton, David E., and Montney, Charles B. Chemical Compounds Vol. 1; Thomson-Gale: Detroit, MI, 2006; pp 46-47.
(2) - Schreiber, Henry D. Curious Chemistry Guides Hydrangea Colors. American Scientist. 2014, 102, 444.
(3) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4-39.
(4) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(5) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(6) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(7) - Halka, Monica and Nordstrom, Brian. Metals & Metalloids; Infobase Publishing: New York, NY, 2011; p 8.
(8) - Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 89.
(9) - Kotz, John C., Treichel, Paul, and Weaver, Gabriela. Chemistry & Chemical Reactivity 6th ed.; Thomson Brooks/Cole: Belmont, CA, 2006; p 166.
(10) - Kotz, John C. and Treichel, Paul. Chemistry & Chemical Reactivity 4th ed.; Thomson Brooks/Cole: Belmont, CA, 1999; p 173.