The chemical reaction that occurs when limestone is placed in water is one of the most important reactions in organic chemistry.
Here is what you should know regarding the reaction of limestone and water.
What Happens When Limestone Is Mixed With Water? (EXPLAINED)
What is limestone?
It is a sedimentary rock that comprises calcite (calcium carbonate) or magnesium (dolomite) and double carbonate of calcium.
It normally forms due to the accumulation of shell fragments, fecal, algae, coral, tiny fossils, and other fossilized debris.
It can also form through the chemical sedimentary processes, including precipitation of calcium carbonate from ocean or lake water.
On close examination, such fossils are visible to the unaided eye of the stone surface.
Limestone is normally gray, but it might also be brown, yellow, or white.
This mineral is a soft rock that you can easily scratch.
It readily effervesces when mixed with any common acid.
Limestones might vary in porosity and texture from coquina, a mixture of pieces of seashells cemented loosely by calcite.
What happens when a piece of limestone is placed in water?
When the limestone, CaCO₃, is placed in the water, carbon dioxide (CO₂) bubbles form.
That is because calcium ions (Ca²+) react with carbonate ions in limestone (CO₃²-) to create calcium carbonate (CaCo3).
The equation for this reaction is: 2 Ca + 2 CO 3 ↔ CaCO 3 + CO 2 ↑+ heat.
Since more hydroxide ions are present than hydrogen ions, the pH level should be greater than 7, making the solution basic.
As the water reaches equilibrium, many other reactions decrease the pH.
The result of these reactions is that the pH level decreases drastically.
Only carbon dioxide bubbles can be seen rising to the water’s surface.
The bubbles are formed when the drop in pH level causes the equilibrium to shift toward carbon dioxide molecules, leaving less room for water molecules.
That is an endothermic reaction, meaning that it absorbs energy, so the surrounding air will feel cool as this reaction occurs.
In summation, carbon dioxide bubbles form when a piece of limestone is placed in water.
The decrease in pH level leads to a reaction that further decreases the pH.
What happens differently if the limestone is powdered vs. in a larger solid piece?
When limestone is powdered, it can undergo a more rapid weathering process called carbonation.
Carbonation speeds up producing the weak carbonic acid by which carbon dioxide dissolves in water and forms bicarbonate and hydrogen ions (acid).
The dissolution of calcium hydroxide, the other calcination product (heating limestone until it turns into lime), also speeds up the process, but it reacts with the hydrogen ions produced by carbonic acid to form water and calcium carbonate.
Another reason why powdered limestone is more reactive than crushed limestone is that exposure to a greater surface area allows for more contact between water and limestone particles.
That exposure can either be achieved by using the coarser powdered form or applying much higher pressure to crushed limestone.
Powdered limestone is typically used when rapid carbonation is desired, such as neutralizing acidic hazardous wastes (such as sulfuric acid).
In contrast, when you place large pieces of limestone into the water, the surface tension of the water decreases.
Limestone comprises mostly calcium carbonate, meaning that placing it in water causes a reaction that releases carbon dioxide gas.
That reduces the surface tension because there are fewer water molecules between the calcium carbonate pieces which means they are further apart.
What happens if the water is warm, hot, vs. boiling?
Limestone is mostly made of calcium carbonate, with very low solubility in boiling water.
If the limestone were crushed into a fine powder, it would dissolve because more surface area would be exposed to the hot water.
If you put a piece of limestone (calcium carbonate) in hot water, it will dissolve similarly and dissolve in boiling water.
The high temperature causes an ionic reaction between the solid calcium carbonate and water to produce gaseous hydrogen and calcium hydroxide.
The calcium hydroxide then reacts with the water to produce calcium hydroxide and hydrogen, leaving excess hydroxide ions in the solution.
Since limestone is made of calcium carbonate, the result is that it disappears.
When you put limestone into warm water, the calcium carbonate slowly dissolves.
The water must become more acidic for precipitation of some solid calcium carbonate.
In other words, when you put limestone into warm water, then it becomes more acidic.
What happens if the limestone being placed in the water has been heated first?
If you place a piece of limestone in heated water, it will bubble and fizz as the gas escapes from the rock.
That is caused by the carbon dioxide that has been locked into the stone over thousands of years.
In reality, this reaction has been used for many years to carbonate water, thus creating effervescent drinks.
Carbon dioxide gas (CO) is slightly soluble in water, meaning that it will dissolve slightly in cold water over time.
However, this reaction is incredibly slow – the amount of CO that reacts with the water each year is minuscule.
When limestone is placed in heated water, it gives off carbon dioxide gas much more noticeably because the reaction occurs so quickly.
As CO dissolves into cold water, it turns carbonic acid (HCO).
In particular, when hot water is added, the heat energy breaks this weak bond and splits apart the CO and the H, and the carbon and hydrogen atoms recombine with oxygen to form CO gas.
That fast-moving reaction results in bubbles of CO forming, which rise to the surface and escape into the air.
A similar process happens when you open a bottle of fizzy drink – initially, flat soda water becomes effervescent because it releases CO.
When limestone is heated, the reaction with water will release more gas than breaking apart carbonic acid because carbon dioxide gas is less soluble in hot water.
You get more dissolved CO per liter of water at higher temperatures.
When limestone (calcium carbonate) comes into contact with water, a chemical reaction occurs.
The limestone dissolves to make a slightly basic solution, so it fizzes if exposed to air.
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