Four samples A, B, C and D change the colour of pH paper or solution to Green, Reddish-pink, Blue and Orange.

Question

(i) Four samples A, B, C and D change the colour of pH paper or solution to Green, Reddish-pink, Blue and Orange. Their pH was recorded as 7, 2, 10.5 & 6 respectively. Which of the samples has the highest amount of Hydrogen ion concentration? Arrange the four samples in the decreasing order of their pH. 

(ii) Rahul found that the Plaster of Paris, which he stored in a container, has become very hard and lost its binding nature. What is the reason for this? Also, write a chemical equation to represent the reaction taking place. 

(iii) Give any one use of Plaster of Paris other than for plastering or smoothening of walls.

Answer 1

(i) a) B 

b) C,A,D,B 

(ii) Due to moisture in the atmosphere it converted into Gypsum 

CaSO₄+\(1\frac{1}{2}\) H₂O \(\longrightarrow\) CaSO₄.2H₂O 

(iii) Making toys/dolls or statues /fixing broken limbs/making decorative materials.