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Calcium Hydroxide - , Toxicity, Properties, Structure, Uses, FAQs

Calcium Hydroxide - , Toxicity, Properties, Structure, Uses, FAQs

Team Careers360Updated on 02 Jul 2025, 04:51 PM IST

In chemistry, calcium hydroxide common name is called slaked lime. Calcium hydroxide is a colorless crystal or white powder. The question arises, “What is the formula of calcium hydroxide?”. The calcium hydroxide formula or chemical formula of calcium hydroxide is Ca(OH)2. It is given the name slaked lime because it is produced when quick lime is mixed with water. Ca(OH)2 chemical name Calcium hydroxide is also produced by the reaction of sodium hydroxide with calcium chloride that is dissolved in water.

This Story also Contains

  1. Properties of Calcium Hydroxide
  2. Toxicity of Calcium Hydroxide
  3. Calcium Hydroxide Uses or Slaked Lime Use
  4. Structure of Calcium Hydroxide
  5. The Acidity of Calcium Hydroxide

Calcium hydroxide also has some other names hydrated lime, builders lime, slaked lime, pickling lime, etc. The solubility of calcium hydroxide is low it is dissociated in water forming OH- ions which indicate that it is basic. The saturated solution or aqueous solution of calcium hydroxide is called lime water. The dissociation of calcium hydroxide in water is shown below.

Ca(OH)2+H2OCa2+(aq)+2 OH-

An appropriate temperature lime dissolves in water to make an alkaline solution with a pH of about 12.5. At high pH values, the hydroxide anion is already present in it so due to the common ion effect the solubility of calcium hydroxide is reduced. When lime is dissolved in water only a touch portion of it dissolves in water and forms lime water and therefore the remaining portion that is not dissolved remains as a suspension and is named as milk of lime. This lime water can also react with acids and thereby forming a salt of calcium hydroxide. Lime water also dissolves some metals like aluminum too. Calcium hydroxide contains two groups so it is a moderate base and its contact with the skin can cause burn also.

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Properties of Calcium Hydroxide

Calcium hydroxide is also known as slaked lime. Calcium hydroxide is a soft, crystalline, white powdery material with a bitter taste. The molecular weight of calcium hydroxide is 74.093 grams per mole with a density of 2.211 grams per centimeter cube. 853K is the melting point of calcium hydroxide. The solubility of calcium hydroxide with water is low and it also reduces on increasing temperature, the solubility product is 5.5×10-6. But its solubility with glycerol and acids is quite high. The reaction of calcium hydroxide with carbon dioxide is called carbonation and its results in the formation of calcium carbonate CaCO3.

Commonly Asked Questions

Q: How does the solubility of calcium hydroxide change with temperature?
A:
Unlike most substances, calcium hydroxide exhibits inverse solubility. Its solubility decreases as temperature increases. This unusual property is due to the exothermic nature of the dissolution process.
Q: How does calcium hydroxide react with carbon dioxide?
A:
Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water. This reaction is the basis for the limewater test for CO2: Ca(OH)2 + CO2 → CaCO3 + H2O. The solution turns cloudy due to the formation of insoluble calcium carbonate.
Q: How does calcium hydroxide interact with proteins?
A:
Calcium hydroxide can denature proteins by disrupting their hydrogen bonds and altering their structure. This property is utilized in some food processing techniques, such as the nixtamalization of corn, where it helps to break down the corn's protein matrix, improving digestibility and nutrient availability.
Q: How does calcium hydroxide compare to other common bases in terms of strength?
A:
Calcium hydroxide is a strong base, but not as strong as alkali metal hydroxides like sodium or potassium hydroxide. Its basicity is due to the complete dissociation of hydroxide ions in solution. However, its lower solubility compared to alkali metal hydroxides results in a slightly lower pH in saturated solutions.
Q: How does calcium hydroxide affect the taste and texture of food products?
A:
Calcium hydroxide can affect food products by:

Toxicity of Calcium Hydroxide

When calcium hydroxide contact with the eye and skin it will cause irritation and burn the skin and consequently eye damage will occurs. Breathing of calcium hydroxide cause irritation to the nose, throat, and lungs thereby causing coughing, wheezing, and breathing problems. When someone breaths calcium hydroxide it will cause problems such as heart disease, lung cancer, respiratory problems, and emphysema. So care must be given while handling with calcium hydroxide when it comes in contact with the skin washing immediately can reduce the effect of calcium hydroxide.

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Commonly Asked Questions

Q: What safety precautions should be taken when handling calcium hydroxide?
A:
When handling calcium hydroxide, one should:
Q: How does calcium hydroxide affect the human body if ingested?
A:
If ingested, calcium hydroxide can cause:
Q: What is the environmental impact of calcium hydroxide use?
A:
The environmental impact of calcium hydroxide includes:
Q: What is the significance of calcium hydroxide in dental applications?
A:
In dentistry, calcium hydroxide is used for:
Q: How does calcium hydroxide affect plant growth when used as a soil amendment?
A:
When used as a soil amendment, calcium hydroxide:

Calcium Hydroxide Uses or Slaked Lime Use

  • Calcium hydroxide is used in sewage treatment as a clarifying agent.

  • It is also used in the paper industry for the conversion of wood to wood pulp.

  • Calcium hydroxide is a very important component for the production of ammonia.

  • As calcium hydroxide is basic so it is used as a pH modifier.

  • For the production of plastics, calcium hydroxide is an important component.

  • It is also present in hair care products.

  • It is used in the production of pesticides and for the manufacture of ebonite.

  • In the processing of sugarcane, a carbonation reaction is used so it involves the use of calcium hydroxide.

  • It is used in the leather industry for the separation of hair or fur from animals.

  • It also has applications in the medical field mainly the dental field. That is the filings used for the process of root canal treatment contain calcium hydroxide.

  • Due to the high pH value of calcium hydroxide, it is used in fresh water treatment for raising the pH value. This is also due to its low toxicity in water and also self-regulating property and it will not raise the pH of water too much.

  • As calcium hydroxide is less toxic it has many applications in the food industry too. Mainly for the pickling of cucumber and other foods.

  • Due to the reaction of calcium hydroxide with carbon dioxide, it is used for the removal of carbon dioxide.

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Commonly Asked Questions

Q: What are the main industrial uses of calcium hydroxide?
A:
Calcium hydroxide has numerous industrial applications, including:
Q: How does calcium hydroxide contribute to the setting of cement?
A:
In cement, calcium hydroxide forms during the hydration of calcium silicates. It contributes to the initial setting and strength development of cement paste. Over time, it reacts with atmospheric CO2 in a process called carbonation, further strengthening the cement.
Q: What is the role of calcium hydroxide in the production of sodium hydroxide?
A:
Calcium hydroxide is used in the lime-soda process to produce sodium hydroxide. It reacts with sodium carbonate (soda ash) to form sodium hydroxide and calcium carbonate: Ca(OH)2 + Na2CO3 → 2NaOH + CaCO3. This process is an alternative to the more common chloralkali process.
Q: How does calcium hydroxide contribute to the Bayer process in aluminum production?
A:
In the Bayer process, calcium hydroxide is used to precipitate impurities from the sodium aluminate solution. It reacts with sodium carbonate and other impurities, forming insoluble calcium compounds that can be easily separated, thus purifying the aluminum-containing solution.
Q: What is the common name for a saturated solution of calcium hydroxide?
A:
A saturated solution of calcium hydroxide is commonly known as limewater. It is a clear, colorless solution used in various applications, including as a test for carbon dioxide in chemistry experiments.

Structure of Calcium Hydroxide

Just like all the metal hydroxide calcium hydroxide also adopts a polymeric structure. The structure of Calcium hydroxide is similar to that of magnesium hydroxide. The bond present in the Calcium hydroxide is ionic as the calcium and the hydroxide are existing in their ionic forms. Ionic bonds exist between Ca2+ and OH- ions. And the calcium metal ion is bonded to two hydroxide ions.

Since the valency of calcium is two plus that it requires two more electrons to complete its octet that is why it directly forms a bond with two hydroxide ions. Calcium hydroxide exists in its polymeric structure in the solid form and this polymeric structure is facilitated by the hydrogen bonding in between the molecules. The structure of calcium hydroxide is shown below.

Structure of calcium hydroxide

Calcium hydroxide reaction with water

Ca(OH)2+H2OCa2+(aq)+2 OH-

Preparation of calcium hydroxide

Calcium hydroxide is found naturally but it is not present in excess so the preparation of calcium hydroxide is necessary. Calcium hydroxide is mainly prepared commercially by the treatment of calcium oxide with water. The following is the reaction taking place on this.

CaO+H2O→Ca(OH)2

Calcium hydroxide is also prepared in the laboratory by the reaction of calcium chloride with sodium hydroxide with NaCl as a byproduct. The following is the reaction taking place on this.

CaCl2+NaOH→Ca(OH)2+NaCl

A white precipitate of Calcium hydroxide is obtained after the reaction.

NCERT Chemistry Notes:

Commonly Asked Questions

Q: What is the structure of solid calcium hydroxide?
A:
Solid calcium hydroxide has a hexagonal crystal structure. Each calcium ion is surrounded by six hydroxide ions in an octahedral arrangement. This structure contributes to its properties, including its relatively low solubility in water compared to other hydroxides.
Q: What is the difference between hydrated lime and calcium hydroxide?
A:
There is no chemical difference between hydrated lime and calcium hydroxide; they are the same compound. "Hydrated lime" is the commercial term for calcium hydroxide, emphasizing that it's the hydrated form of lime (calcium oxide). The term is commonly used in construction and agriculture.
Q: What is the relationship between calcium hydroxide and hardness in water?
A:
Calcium hydroxide can contribute to water hardness when it dissociates, releasing calcium ions. However, it's more commonly used to reduce water hardness through the lime softening process. In this process, calcium hydroxide precipitates dissolved calcium and magnesium ions as insoluble carbonates, effectively softening the water.
Q: How does calcium hydroxide react with acids?
A:
Calcium hydroxide reacts with acids in a neutralization reaction, forming water and a calcium salt. For example, with hydrochloric acid: Ca(OH)2 + 2HCl → CaCl2 + 2H2O. This reaction is exothermic and is the basis for using calcium hydroxide in antacid medications and for neutralizing acidic industrial waste.
Q: How does the presence of calcium hydroxide affect concrete durability?
A:
Calcium hydroxide in concrete:

The Acidity of Calcium Hydroxide

Calcium hydroxide is a compound containing two hydroxyl groups so it gives two hydroxyl ions per molecule upon dissociation it can be regarded as a di acidic molecule. Hence the acidity of Calcium hydroxide is 2. The dissociation of calcium hydroxide can be shown below.

Ca(OH)2Ca2++2OH-

This two hydroxyl group is responsible for the acidity of the medium.

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Commonly Asked Questions

Q: Why is calcium hydroxide considered a strong base?
A:
Calcium hydroxide is considered a strong base because it dissociates completely in water, releasing a high concentration of hydroxide (OH-) ions. This results in a high pH solution, typically around 12.5, making it strongly alkaline.
Q: How does calcium hydroxide affect soil pH?
A:
Calcium hydroxide is used as a soil amendment to increase soil pH, reducing acidity. When added to soil, it neutralizes hydrogen ions, raising the pH. This process, known as liming, improves soil structure and nutrient availability for plants.
Q: What is the difference between calcium hydroxide and calcium oxide?
A:
Calcium hydroxide (Ca(OH)2) is a hydrated form of calcium oxide (CaO). Calcium oxide, also known as quicklime, is anhydrous and reacts vigorously with water to form calcium hydroxide. Calcium hydroxide is less reactive and has different applications due to its alkaline properties in solution.
Q: What is calcium hydroxide and how is it formed?
A:
Calcium hydroxide, also known as slaked lime, is an inorganic compound with the chemical formula Ca(OH)2. It is formed when calcium oxide (quicklime) reacts with water in a process called slaking. The reaction is exothermic, releasing heat: CaO + H2O → Ca(OH)2.
Q: How does calcium hydroxide contribute to food preservation?
A:
Calcium hydroxide is used in food preservation due to its alkaline nature. It's used in processes like:

Frequently Asked Questions (FAQs)

Q: How does calcium hydroxide affect the properties of mortar?
A:
In mortar, calcium hydroxide:
Q: What is the significance of calcium hydroxide in the treatment of acid mine drainage?
A:
In treating acid mine drainage, calcium hydroxide:
Q: How does calcium hydroxide contribute to the Solvay process for sodium carbonate production?
A:
In the Solvay process, calcium hydroxide plays a role in the recovery of ammonia:
Q: What is the effect of calcium hydroxide on the germination of seeds?
A:
Calcium hydroxide can affect seed germination in several ways:
Q: How does calcium hydroxide contribute to the removal of phosphates in wastewater treatment?
A:
In wastewater treatment, calcium hydroxide removes phosphates through:
Q: What is the role of calcium hydroxide in the production of biodiesel?
A:
In biodiesel production, calcium hydroxide can be used as a heterogeneous catalyst for the transesterification reaction. Its benefits include:
Q: How does calcium hydroxide affect the corrosion of metals?
A:
Calcium hydroxide affects metal corrosion in several ways:
Q: What is the role of calcium hydroxide in wastewater treatment?
A:
In wastewater treatment, calcium hydroxide is used for:
Q: What is the role of calcium hydroxide in the pulp and paper industry?
A:
In the pulp and paper industry, calcium hydroxide is used in the Kraft process for:
Q: What is the role of calcium hydroxide in leather tanning?
A:
In leather tanning, calcium hydroxide is used in the liming process to:
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