Question

on adding a few drops of universal indicator in three colourless solution X Y and Z test tube a student observed the changes in colours green in X and red in Y and blue in Z
(a)X Y and Z in increasing order of their PH value
(b)which one of the three X Y and Z will change the colour of phenolphtalein ?why?​

Answer 1

a.   Y X Z .  ( INCREASING ORDER OF THEIR PH VALUE)

b.   Z will change the color of phenolphthalein to pink color  because it is basic in nature.

Answer 2

(a) X Y and Z in increasing order of their PH value are Y < X < Z.

- X shows green colour ⇒ X is neutral ⇒ its pH is 7

- Y shows red colour ⇒ Y is acidic ⇒ its pH is <7

- Z shows blue colour ⇒ Z is basic ⇒ its pH is >7

(b) Z will change the colour of phenolphtalein.

- Phenolphthalein is originally colourless.

- But in basic mediums in pH range of around 8.2-10, it turns pink.

- Since Z has a pH>7 and only it is basic among the three given solutions, so it will chane the colour of phenolphthalein