Turmeric is a type of powder which belongs to ginger family and is called zingiberaceae. Turmeric is used both as spice and as a natural Dyce also. The yellow colour of turmeric is due to presence of compound cur cumin.
This compound which is present in
turmeric is due to hydroxyl groups. This compound does not undergo any change
in an acidic medium but it changes in basic medium.
In addition to this compound, there is
another compound called phenolphthalein which resembles this substance. This
phenolphthalein is colourless in nature. Both this substance does not change
its colour in acidic medium but in basic medium turmeric turns reddish brown
and phenolphthalein turns pink.
Another substance which does not changes
its colour in basic medium but changes its colour in acidic medium in methyl
orange. It turns pink in acidic medium. Thus, turmeric powder turns red because
slaked lime which is nothing but calcium hydroxide is added to it and it
becomes red. When any such substance will be added to red turmeric will turn
yellow. This is the reason why turmeric powder turns red when mixed with slaked
lime.