Why is Plaster of Paris written as CaSO 4 . 1 2 H 2 O ? How is it possible to have half a water molecule attached to CaSO 4 ?

Plaster of Paris is prepared by heating gypsum at 373 K . The balanced equation is as follows: CaSO 4 . 2 H 2 O Gypsum → 373 k CaSO 4 . 1 2 H 2 O Plaster of paris + 3 2 H 2 O Water . It is not possible to have half a molecule of water. Therefore, actual formula must be 2 CaSO 4 . H 2 O . This means that, two molecules of calcium sulphate shares one molecule of water. Thus, the effective number of water molecules for one calcium sulphate is half. However, for the sake of simplicity, the plaster of Paris is shown as CaSO 4 . 1 2 H 2 O . That is, only half water molecule is shown as the water of crystallisation.

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What is the use of calcium sulphate?

Important Questions on Acids, Bases and Salts

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Write the chemical formulae for Washing-soda and Baking soda and give their uses.

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Why should a magnesium ribbon be cleaned before burning in air?

MEDIUM

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Why should a magnesium ribbon be cleaned before burning in the air?

HARD

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How is washing soda prepared from sodium carbonate? Give its chemical equation. State the type of this salt. Name the type of hardness of water which can be removed by it?

MEDIUM

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Baking soda is a mixture of:

HARD

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How is sodium hydroxide manufactured in industries? Name the process. In this process, a gas X is formed as a by-product. This gas reacts with lime water to give a compound Y, which is used as a bleaching agent in the chemical industry. Identify X and Y and write the chemical equation of the reaction involved.

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The chemical formula for plaster of Paris is:

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The

pH

of a salt used to make tasty and crispy pakoras is 14. Identify the salt and write a chemical equation for its formation. List its two uses.

HARD

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What happens when bleaching powder reacts with dilute sulphuric acid? Give equation of the reaction involved.

HARD

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Why is Plaster of Paris written as

{CaSO}_{4} . \frac{1}{2} H_{2} O

? How is it possible to have half a water molecule attached to

{CaSO}_{4}

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State two important uses of bleaching powder.

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What is Plaster of Paris? Write the chemical formula of Plaster of Paris.

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The blue colour of crystals of a substance changed to white on heating in a closed test tube but the colour was regained after sometime on cooling. Name the substance and write its chemical formula. Explain the phenomenon involved.

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How is Plaster of Paris prepared? Write chemical equation of the reaction involved.

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Name the sodium compound which is used for softening hard water.

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What is meant by 'hydrated' and 'anhydrous' salts? Explain with examples.

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