Cement & Test for Calcium Ions | Chemistry for JAMB PDF Download

Chemical Composition of Cement and the Setting of Mortar

• Cement is a crucial component in construction materials, providing binding properties to hold structures together.
• The chemical composition of cement mainly consists of four primary compounds:
  • Tricalcium silicate (C₃S): It is the major compound and contributes to the early strength of cement.
  • Dicalcium silicate (C₂S): It is the second most abundant compound and contributes to the long-term strength of cement.
  • Tricalcium aluminate (C₃A): It is responsible for the initial setting of cement and contributes to its early strength development.
  • Tetracalcium aluminoferrite (C₄AF): It provides limited strength contribution and contributes to the color of cement.
• Cement may also contain small amounts of other compounds, such as gypsum, which regulates the setting time of cement.
• The setting of mortar occurs when cement is mixed with water, resulting in a chemical reaction known as hydration.
• During hydration, water reacts with the compounds in cement to form hydration products, including calcium silicate hydrate (C-S-H) gel, calcium hydroxide (Ca(OH)₂), and ettringite (hydrated calcium aluminum sulfate).
• The formation of hydration products leads to the hardening of mortar and the development of strength over time.

Test for Ca²⁺

Calcium ions (Ca²⁺) are commonly found in various compounds and play essential roles in biological, industrial, and environmental contexts.
To test for the presence of Ca²⁺ ions, the following methods can be employed:

• Flame Test: When a compound containing Ca2⁺ ions is heated in a flame, it imparts an orange-red color to the flame.
• Calcium Hydroxide Test: Addition of a few drops of calcium hydroxide (lime water) to a solution suspected to contain Ca²⁺ ions results in the formation of a white precipitate of calcium carbonate.
• EDTA Titration: Complexometric titration using ethylenediaminetetraacetic acid (EDTA) can quantitatively determine the concentration of Ca²⁺ ions in a solution. EDTA forms a stable complex with Ca2+ ions, and the endpoint is detected using a suitable indicator such as Eriochrome Black T.
• Atomic Absorption Spectroscopy (AAS): AAS is an instrumental technique used for the qualitative and quantitative analysis of metal ions, including Ca²⁺. It measures the absorption of light by the metal ions and provides accurate results.

Conclusion

In conclusion, the chemical composition of cement consists primarily of tricalcium silicate (C₃S), dicalcium silicate (C₂S), tricalcium aluminate (C₃A), and tetracalcium aluminoferrite (C₄AF). These compounds undergo hydration when mixed with water, resulting in the setting and hardening of mortar.