Portland cement is a key ingredient in concrete and is widely used in the construction industry. A crucial component of Portland cement is gypsum, which is added for a specific reason related to the setting time of the cement.
Gypsum, chemically known as calcium sulfate dihydrate, is represented by the formula \(CaSO_4.2H_2O\). It plays a significant role in the hydration process of cement. Here's how:
Role in Setting Time: When water is added to Portland cement, highly reactive compounds like tricalcium aluminate (C3A) can lead to rapid setting of cement, which is undesirable. Gypsum slows down this setting process by reacting with C3A to form ettringite, allowing more working time.
Importance of Gypsum: Without gypsum, the cement would set very quickly after mixing with water, making it difficult to work with and reducing its strength and stability in the long run.
To conclude, in Portland cement, 'X' to enhance the setting time refers to \(CaSO_4.2H_2O\), which is gypsum. This component ensures the cement does not set too quickly, thereby improving its usability in construction.
Let's evaluate the options:
\(CaSO_4.\frac 12 H_2O\): This is not used to control the setting time of cement.
\(CaSO_4.2H_2O\): Correct! This is gypsum, which is used to regulate the setting time.
\(CaSO_4\): This form lacks the hydration that is important for setting control.
\(CaCO_3\): This is calcium carbonate, not relevant to setting time control.
Thus, the correct answer is \(CaSO_4.2H_2O\).
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When mixed with water, the setting of cement takes place to give a hard mass. This is due to the hydration of the molecule of the constituents and their rearrangement. The purpose of adding gypsum \((CaSO_4.2H_2O)\) is only to slow down the process of setting of the cement so that it gets sufficiently hardened.
S-block elements, also known as alkali and alkaline earth metals, constitute the first two groups of the periodic table.
Group 1 elements, including hydrogen, lithium, sodium, potassium, rubidium, cesium, and francium, are alkali metals characterized by low density, high reactivity, and the ability to form strong bases when combined with water. They showcase a single valence electron in their outermost shell, making them eager to lose it in chemical reactions.
Group 2 elements, beryllium, magnesium, calcium, strontium, barium, and radium, make up the alkaline earth metals in Group 2. These metals share similar properties, such as higher densities and melting points compared to alkali metals. They also have a tendency to form ionic compounds with nonmetals.
S-block elements play vital roles in various industrial and biological processes. Alkali metals find applications in batteries, while alkaline earth metals are crucial for construction materials and are essential nutrients for living organisms. Despite their importance, the reactivity of alkali metals requires careful handling, often stored in oil to prevent reactions with moisture or oxygen. Overall, s-block elements contribute significantly to the diverse applications of chemistry in our daily lives.
