Test: Cement & Calcium Ions - JAMB MCQ

The primary chemical composition of cement is calcium oxide (CaO). It is obtained from limestone, which is primarily composed of calcium carbonate (CaCO₃). During the manufacturing process of cement, limestone is heated, resulting in the decomposition of calcium carbonate to calcium oxide and carbon dioxide.

Tricalcium aluminate (Ca₃Al₂O₆) is responsible for the initial setting of cement. It reacts with water to form calcium aluminate hydrate compounds, which initiates the setting process by generating heat and forming a solid structure.

The setting of cement occurs through the process of hydration. When water is added to cement, it reacts with the compounds present in cement, such as tricalcium silicate (Ca₃SiO₅) and tricalcium aluminate (Ca₃Al₂O₆), forming calcium silicate hydrate and calcium aluminate hydrate compounds. This chemical reaction leads to the hardening and solidification of cement.

Gypsum (calcium sulfate dihydrate, CaSO₄ · 2H₂O) is added to cement during its manufacturing to regulate the setting time. Gypsum slows down the hydration process of cement, extending the setting time and allowing for better workability and handling of the cement before it hardens.

Tricalcium silicate (Ca₃SiO₅) contributes to the final strength of cement. It undergoes a chemical reaction with water during hydration, forming calcium silicate hydrate (C-S-H) gel. This gel structure provides the binding and strength characteristics of cement.

The test for Ca²⁺ ions involves the addition of silver nitrate (AgNO₃) as a reagent. When silver nitrate is added to a solution containing calcium ions, a white precipitate of calcium carbonate (CaCO₃) is formed, indicating the presence of calcium ions.

The chemical formula of calcium sulfate is CaSO₄. It is a compound that exists in different forms, such as anhydrous calcium sulfate (CaSO₄) and calcium sulfate dihydrate (CaSO₄ · 2H₂O), commonly known as gypsum.

When calcium ions (Ca2⁺) react with sodium carbonate (Na₂CO₃), the compound formed is calcium carbonate (CaCO₃). This reaction can be represented as follows: Ca²⁺ + CO₃^2- → CaCO₃.

The concentration of Ca²⁺ ions in a solution can be determined using various methods, including titration, gravimetric analysis, and spectrophotometry. Titration involves the use of a standardized solution to react with the calcium ions and determine their concentration. Gravimetric analysis involves the precipitation of calcium ions as a solid compound, which is then weighed to calculate the concentration. Spectrophotometry measures the absorption or emission of light by the calcium ions to determine their concentration.

The test for Ca²⁺ ions results in the formation of a white precipitate of calcium hydroxide (Ca(OH)₂). When calcium ions react with hydroxide ions, calcium hydroxide is formed and appears as a white precipitate, indicating the presence of calcium ions in the solution.