Limestone

The Best Source of Hydroxide


 

AQUA OH!TM ROCKS… Literally!!

 
The hydroxide found in AQUA OH!™ is sourced from limestone so AQUA OH!™ is literally rock. This article seeks to explain the natural phenomenon that is limestone and the secrets hidden within.

The Circle

canyon-imgWater is the source of all life on earth. Water also brings into being and transforms many inorganic substances. Limestone is a chief example of this. Although not living and therefore inorganic, limestone is still classified as an organic sedimentary rock because it is made up of skeletal and shell fragments from coral and other lifeforms that existed in water eons ago. These collected at the bottom of bodies of water and then were transformed over millions of years. So from the remnants of life that existed in water comes the elements that constitute limestone.

The life cycle of water and limestone does not end with its formation. They continue their dance and create some of the most beautiful sights in nature. Bryce Canyon in Utah would be a prime example of this. Wind and rain have combined to paint a panoramic picture of vivid colors with limestone as the canvas.

But an even more impressive interplay between water and limestone are caves. Most caves in the world are formed in limestone. Rainwater picks up carbon dioxide as it falls and also in the soil itself. It then becomes a weak acid as it percolates through the soil. Over time this acid eats away at the limestone, enlarging fissures, joints, and fractures found in the stone. Water always seeks to find the water table and will use whatever means necessary to get there. As caves are formed, water plays a secondary role in the system.

Besides enlarging and altering the current cave system, it also transforms the already developed cave rooms. As the now acidified water travels through bedrock it dissolves the limestone, taking calcium carbonate with it. As it enters the cave room the carbon dioxide is released as a gas and the calcium carbonate is left behind to form Stalactites, stalagmites, and other formations. While a cave is still undergoing this process of change in the presence of water, it is said to be living because the rock formations are continuously growing and transforming. When a cave dries out it is said to die because these processes stop. So the combination of water, carbon dioxide, and calcium carbonate are the main ingredients that produce living caves. These three ingredients play a large role in limestone and its many uses. But the dance between water and limestone does not end there and a new partner joins the dance – heat.

cave-imgIn the most basic terms limestone is made up of three elements calcium, carbon, and oxygen in the form of calcite, a crystalline form of calcium carbonate. When heat is applied, limestone releases carbon dioxide and transforms into burnt lime which is calcium and oxygen in the form of calcium oxide. Burnt lime is very reactive and will return to calcium carbonate if it comes into contact with carbon dioxide. There is a very circular relationship between calcium carbonate, carbon dioxide, and calcium oxide with heat being the major catalyst.

Another circular relationship exists between burnt lime and water. When burnt lime is partially hydrated it produces heat by an exothermic reaction. The result of this reaction is not only heat but also a new product called hydrated lime. Hydrated lime is a white powdery substance made up of three elements: calcium, oxygen, and hydrogen in the form of calcium hydroxide. Hydrated lime is more stable than burnt lime but will still react with carbon dioxide. The result will be calcium carbonate suspended in water. Hydrated lime can also be turned back into burnt lime by heating which will remove the water but leave the calcium oxide.

Although hydrated lime is a white powdery substance, it is also relatively soluble in water. When hydrated lime is added to water it suspends in the water. The result is a substance called limewater. If more calcium hydroxide is added until a fully saturated solution is formed then it is called milk of lime. Several factors are necessary to get a fully saturated solution.

First, the saturation level of calcium hydroxide is temperature dependent meaning it may be more or less depending on the temperature. We use ambient temperature so that no heating or cooling of the solution is necessary.

Second, the water dissolves the calcium hydroxide molecules by breaking them down into calcium ions and hydroxide ions. For every one calcium ion there are two hydroxide ions because calcium hydroxide is divalent. Divalent means each calcium ion has two extra protons for the hydroxide ions to bind with. Since each hydroxide ion only has one extra electron, it takes two to combine with one calcium to gain balance. Water dissolves this bond releasing the ions in a one to two ratio.

Third, for full saturation to take place there must be solubility equilibrium. This means there must be an equal amount of undissolved calcium hydroxide molecules in proportion to the released calcium and hydroxide ions. This equilibrium is also called dynamic equilibrium since the ions and molecules freely combine and break apart in the solution.

Finally, points two and three above demonstrate there are two separate balancing acts taking place in the saturated solution: one between the calcium and hydroxide ions and one between the dissolved ions and undissolved calcium hydroxide molecules.

Let me illustrate with an example. The specific numbers are not relevant rather the ratio between each is. At room temperature 10 calcium hydroxide molecules are added to 20 water molecules. The water dissolves 5 of these calcium hydroxide molecules breaking them down into 5 calcium ions and 10 hydroxide ions. In order to maintain equilibrium, 5 of the calcium hydroxide molecules remain suspended in the water but are undissolved. Therefore we end up with a saturated solution made up of 20 water molecules within which are suspended 5 calcium ions, 10 hydroxide ions, and 5 calcium hydroxide molecules.

It is at this point that we begin our natural processes that allow us to remove most of the calcium ions and the calcium hydroxide molecules while still leaving the hydroxide ions suspended in the water. It is the hydroxide that is the transformative component in calcium hydroxide and it is water that unlocks its potential. So from the dance between limestone, water, and heat comes a powerful acid hunter that can neutralize acid by merely creating water. And so the journey ends where it began with water.

For a detailed explanation of the chemistry involved in the manufacture of AQUA OH!™ visit The Chemistry Behind Hydroxide Alkaline Water.