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Standard VIII

Chemistry

Characteristics of Chemical Reaction

Write an equa...

Question

Write an equation to show the reaction between Plaster of Paris and water?

C a S O_{4} . \frac{1}{2} H_{2} O P l a s t e r o f P a r i s + \frac{3}{2} H_{2} O W a t e r ⟶ C a S O_{4} .2 H_{2} O G y p s u m

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C a S O_{4} . H_{2} O P l a s t e r o f P a r i s + \frac{3}{2} H_{2} O W a t e r ⟶ C a S O_{4} . \frac{5}{2} H_{2} O G y p s u m

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C a S O_{4} . H_{2} O P l a s t e r o f P a r i s + H_{2} O W a t e r ⟶ C a S O_{4} .2 H_{2} O G y p s u m

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C a S O_{4} . \frac{1}{2} H_{2} O P l a s t e r o f P a r i s + \frac{1}{2} H_{2} O W a t e r ⟶ C a S O_{4} . H_{2} O G y p s u m

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Solution

The correct option is A $C a S O_{4} . \frac{1}{2} H_{2} O P l a s t e r o f P a r i s + \frac{3}{2} H_{2} O W a t e r ⟶ C a S O_{4} .2 H_{2} O G y p s u m$
Plaster of Paris when reacts with water liberating heat through crystallization. Gypsum is produced by heating plaster of paris to about 150-degree Celsius. When the dry plaster of paris powder is mixed with water it reforms into gypsum. Depending upon the temperature gypsum converts to hemihydrate or anhydrous form.
$C a S O_{4} . \frac{1}{2} H_{2} O P l a s t e r o f P a r i s + \frac{3}{2} H_{2} O W a t e r ⟶ C a S O_{4} .2 H_{2} O G y p s u m$

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Similar questions

Q. Match List - I with List - II for the compositions of substances and select the correct answer using the code given below the list:
List - I List - II
Substances Composition
(A) Plaster of paris (i)

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

(B) Epsomite (ii)

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

M a S O_{4} \cdot 7 H_{2} O

(D) Gypsum (iv)

M g S O_{4} \cdot H_{2} O

(v)

C a S O_{4}

$\begin{matrix} List I & List II 1. Plaster of Paris & a. C a S O_{4} .2 H_{2} O 2. Epsomite & b. C a S O_{4} .1 / 2 H_{2} O 3. Kieserite & c. M g S O_{4} .7 H_{2} O 4. Gypsum & d. M g S O_{4} . H_{2} O e. C a S O_{4} \end{matrix}$

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)

The

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)

are

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

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

and

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

respectively. The respective values of their standard entropies are

194.0

130.0

and

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}

) of

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

is equal to:

Q. Question 32
Match the important chemicals given in Column I with the chemical formulae given in Column II.

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