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What is the role of gypsum, CaSo4.2H2O i...

What is the role of gypsum, `CaSo_4.2H_2O` in setting of cement? Identify the correct option from the following:

A

to fasten the setting process

B

to provide water molecules for hydration process

C

to help to remove water molecules

D

to slow down the setting process

Text Solution

Verified by Experts

The correct Answer is:
D
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Concrete is produced form a mixture of cement, water and small stones. Small amount of gypsum, CaSO_(4).2H_(2)O is added in cement production to improve the subsequent hardening of concrete. The elevated temperature during the production of cement may lead to the formation of unwanted hemihydrate CaSO_(4)(1)/(2)H_(2)O according to reaction. CaSO_(4)2H_(2)O(s) rarr CaSO_(4)(1)/(2)H_(2)O(s)+(3)/(2)H_(2)O(g) The Delta_(f)H^(Theta) of CaSO_(2).2H_(2)O(s),CaSO_(4)(1)/(2)H_(2)O(s),H_(2)O(g) are -2021.0 kJ mol^(-1), -1575.0 kJ mol^(-1) and -241.8 kJ mol^(-1) , respectively. The respective values of their standard entropies are 194.0, 130.0 and 188.0 J K^(-1)mol^(-1) . The values of R = 8.314JK^(-1)mol^(-1) = 0.0831L bar mol^(-1)K^(-1) . Answer the following questions on the basis of above information. Heat change occurring during conversion of 1kg of CaSO_(4).2H_(2)O(s) (molar mass 172g mol^(-1)) of CaSO_(4)(1)/(2)H_(2)O(s) is equal to

For real gases, van der Waals' equation is written as (P+(an^(2))/(V^(2))) (V-nb)= nRT where a and b are van der Waals' constants. Two sets of gases are: (I) O_(2), CO_(2), H_(2) and He(II) CH_(4), O_(2) and O_(2) and H_(2) The gases given in set I in increasing order of b and gases given in set II in decreasing order of a are arranged below. Select the correct order from the following:

For real gases, van der Waals' equation is written as (P+(an^(2))/(V^(2))) (V-nb)= nRT where a and b are van der Waals' constants. Two sets of gases are: (I) O_(2), CO_(2), H_(2) and He(II) CH_(4), O_(2) and O_(2) and H_(2) The gases given in set I in increasing order of b and gases given in set II in decreasing order of a are arranged below. Select the correct order from the following:

Hydrated calcium sulphate has the formula of CaSO_4 . 2H_2O . What is the name given to the water molecules present in the salt ?