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Uses of Slaked Lime

What is the p...

Question

What is the product formed when hydrated $C a S O_{4}$ is heated to $125^{o} C$ instead of $200^{o} C$ ?

A

(C a S O_{4}) \frac{1}{2} H_{2} O

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B

C a S O_{4} \frac{3}{4} H_{2} O

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C

C a S O_{4}

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D

C a O + S O_{3}

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Solution

The correct option is A $(C a S O_{4}) \frac{1}{2} H_{2} O$
Then plaster of paris $(C a S O_{4}) . \frac{1}{2} H_{2} O$ forms.
Reaction is:
$(C a S O_{4}) .2 H_{2} O \to (C a S O_{4}) . \frac{1}{2} H_{2} O$

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Similar questions

Q. Concrete is produced from a mixture of cement, water and small stones. A small amount of gypsum,

C a S O_{4} \cdot 2 H_{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

C a S O_{4} \cdot \frac{1}{2} H_{2} O

according to reaction.

C a S O_{4} \cdot 2 H_{2} O (s) \to C a S O_{4} \cdot \frac{1}{2} H_{2} O (s) + \frac{3}{2} H_{2} O (g)

Δ_{f} H^{⊖}

C a S O_{4} \cdot 2 H_{2} O (s), C a S O_{4} \frac{1}{2} H_{2} O (s), H_{2} O (g)

- 2021.0 k J m o l^{- 1}

- 1575.0 k J m o l^{- 1}

- 241.8 k J m o l^{- 1}

respectively. The respective values of their standard entropies are

194.0

130.0

188.0 J K^{- 1} m o l^{- 1} .

R = 8.314 J K^{- 1} m o l^{- 1} = 0.0831 L b a r m o l^{- 1} K^{- 1}

Answer the follwoing questions on the basis of above information.

Heat change occuring during conversion of

1 K g

C a S O_{4} \cdot 2 H_{2} O (s)

(molar mass 172 g mol

^{- 1}

C a S O_{4} \cdot \frac{1}{2} H_{2} O (s)

Q. Concrete is produced from a mixture of cement, water and small stones. Small amount of gypsum,

C a S O_{4} \cdot 2 H_{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

C a S O_{4} \cdot \frac{1}{2} H_{2} O

according to reaction.

C a S O_{4} \cdot 2 H_{2} O (s) \to C a S O_{4} \cdot \frac{1}{2} H_{2} O (s) + \frac{3}{2} H_{2} O (g)

Δ_{f} H^{⊖}

C a S O_{4} \cdot 2 H_{2} O (s), C a S O_{4} \frac{1}{2} H_{2} O (s), H_{2} O (g)

- 2021.0 k J m o l^{- 1}

- 1575.0 k J m o l^{- 1}

- 241.8 k J m o l^{- 1}

respectively. The respective values of their standard entropies are

194.0

130.0

188.0 J K^{- 1} m o l^{- 1} .

R = 8.314 J K^{- 1} m o l^{- 1} = 0.0831 L b a r m o l^{- 1} K^{- 1}

Answer the follwoing questions on the basis of above information.

The value of equilibrium constant for reaction is:

$C a S O_{4} .2 H_{2} O Δ 120^{\circ} C - ----- \to A - - + 3 H_{2} O . A$ is

Q. When gypsum is heated to

393 K

Q. 0.5 moles of

H_{2} S O_{4}

is mixed with 0.2 moles of

C a (O H)_{2} .

The maximum number of moles of

C a S O_{4}

formed is:
Reaction:

H_{2} S O_{4} + C a (O H)_{2} \to C a S O_{4} + 2 H_{2} O

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