Question

Which of the following statements is false? (1) Calcium oxide is also called quick lime or burnt lime. (2) Slaking is a process of dissolving quick lime in water. (3) Suspension of slaked lime in water is called milk of lime. (4) The clear solution of slaked lime in water is called lime water.

Short answer

Statement 2 is false.

Step-by-step solution

- Understanding Calcium Compounds

Identify the terms used in the context, such as quick lime (calcium oxide), slaked lime (calcium hydroxide), milk of lime, and lime water. Quick lime (CaO) reacts with water to form slaked lime (Ca(OH)2).

- Analyze Statement 1

Statement 1: Calcium oxide is also called quick lime or burnt lime. This is true as calcium oxide (CaO) is commonly known as quick lime or burnt lime.

- Examine Statement 2

Statement 2: Slaking is a process of dissolving quick lime in water. Actually, slaking (or slaking lime) refers to the process of adding water to quick lime to form slaked lime (Ca(OH)2). It is not just dissolving but a chemical reaction.

- Consider Statement 3

Statement 3: Suspension of slaked lime in water is called milk of lime. This is true, as milk of lime refers to a suspension of calcium hydroxide (slaked lime) in water.

- Evaluate Statement 4

Statement 4: The clear solution of slaked lime in water is called lime water. This is also true, as lime water is the clear, aqueous solution of calcium hydroxide.

- Identify the False Statement

Based on the analysis, the false statement is Statement 2. Slaking is not simply dissolving quick lime in water but involves a chemical reaction to form calcium hydroxide.

Key concepts

calcium oxide

Calcium oxide, also known as quick lime or burnt lime, is a chemical compound with the formula CaO. It is a white, caustic, alkaline, crystalline solid at room temperature. Quick lime is produced by heating calcium carbonate (such as limestone) in a kiln to a temperature above 900°C. This process is called calcination. Quick lime reacts with water in a vigorously exothermic reaction to form calcium hydroxide (slaked lime). This reaction releases a significant amount of heat and produces steam. Quick lime is widely used in various industries, including construction (for making cement and lime mortar), agriculture (for soil pH adjustment), and environmental management (for water and sewage treatment).

• Formula: CaO
• Also known as: Quick lime, burnt lime
• Production: By heating calcium carbonate
• Uses: Construction, agriculture, water treatment

slaking process

The slaking process refers to the addition of water to calcium oxide (quick lime) to produce calcium hydroxide (slaked lime). This is more than a simple dissolution; it is a chemical reaction known as hydration. When water is added to quick lime, a vigorous reaction ensues, producing calcium hydroxide, steam, and releasing a substantial amount of heat. The balanced chemical equation for this reaction is: \[ CaO + H_2O \rightarrow Ca(OH)_2 \ \]
The resulting calcium hydroxide can be in the form of a dry powder or a slurry, depending on the amount of water used. If a limited amount of water is added, the product is a dry solid; with excess water, a creamy slurry is formed. This slurry is referred to as milk of lime.

• Involves: Water and quick lime
• Produces: Calcium hydroxide
• Exothermic: Releases heat
• Equation: \[ CaO + H_2O \rightarrow Ca(OH)_2 \]

calcium hydroxide

Calcium hydroxide, also known as slaked lime, is a chemical compound with the formula Ca(OH)_2. It is formed by the reaction of calcium oxide with water in the highly exothermic slaking process. Calcium hydroxide appears as a white powder or in a suspension called milk of lime. In its solid form, it is slightly soluble in water. However, it forms a clear solution known as lime water. Calcium hydroxide finds applications in various fields, such as in construction for making plasters and mortars, in the food industry for processing sugarcane and maize tortillas, and in environmental management for neutralizing acidic soils and treating wastewater.

• Formula: Ca(OH)_2
• Also known as: Slaked lime
• Production: By slaking quick lime
• Uses: Construction, food industry, wastewater treatment

lime water

Lime water is the clear, aqueous solution of calcium hydroxide (slaked lime) in water. It is formed by dissolving calcium hydroxide in water to the point of saturation. Lime water has a slightly bitter taste and is alkaline in nature. It is used in various applications, including laboratory experiments to detect the presence of carbon dioxide gas. When carbon dioxide is passed through lime water, it turns milky due to the formation of calcium carbonate. The reaction is given by: \[ Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \ \]
Lime water also has applications in the food processing industry for the clarification of raw juice in sugar refining, and in the treatment of potable water and industrial wastes.

• Composition: Aqueous solution of calcium hydroxide
• Taste: Slightly bitter
• Nature: Alkaline
• Uses: Detecting CO_2, food processing, water treatment