Which of the following statements are not correct? 1. Plaster of Paris is obtained on heating gypsum. 2. Sodium carbonate is an important constituent of baking powder. 3. Bleaching powder can also act as an oxidising agent. 4. Ten water molecules are present in one formulae unit of chemical species of a sample with common name blue vitriol. 5. Sodium hydroxide is produced by passing electricity through the aqueous solution of sodium chloride.

Official answer key: C, the same as the academy’s answer shown above.

Baking Powder

• Two chemicals make up the mixture that makes baking powder. The two chemicals are sodium bicarbonate and sodium hydrogen carbonate, respectively. Hence, statement 2 is incorrect.
• Sodium hydrogen carbonate is another name for sodium bicarbonate.
• Ten water molecules are present in one formulae unit of chemical species
• The compound whose one formula unit is associated with 10 water molecules is sodium carbonate decahydrate (Na2CO3.10H2O) commonly known as washing soda. Hence, statement 4 is incorrect. Blue vitriol is another name for copper sulphate pentahydrate.
• It is prepared by heating baking soda and then recrystallizing the product so obtained.

Plaster of Paris

• Plaster of Paris is manufactured by heating gypsum at 373 – 393 K or 150° C/300° F.
• Hence, statement 1 is correct.
• On heating gypsum at 373 – 393 K, it loses water molecules and becomes calcium sulphate hemihydrate.
• This product is known as the plaster of Paris.

Bleaching Powder

• Bleaching powder is a powder with a pale yellow colour and a strong chlorine odour.
• It is solvent in water yet because of the presence of contaminations, we never notice a reasonable arrangement.
• Calcium hypochlorite is its chemical name, and its formula is Ca (OCl2).
• Bleaching powder is a good oxidizing agent hence it can be used in bleaching action.

Sodium Hydroxide

• The aqueous solution of sodium chloride, known as brine, breaks down into sodium hydroxide when electricity is applied to it. Hence statement 5 is correct.
• The method is known as the chloralkali process due to the fact that the products produced chlor for chlorine and sodium hydroxide for alkali.