Soap, being basic in nature, reacts with the acidic components of the curry stain, resulting in neutralization. This reaction forms salts and water, which may have a reddish-brown color due to the presence of the remaining components of the stain along with the soap.
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The reddish-brown color seen when scrubbing a curry stain on white cloth with soap is due to the chemical reaction between the pigments in the curry and the soap. Many curries contain turmeric, a natural yellow-orange pigment. When this pigment comes into contact with soap, which is often alkaline, it undergoes a chemical reaction called saponification.
During saponification, the alkaline environment of the soap causes the turmeric pigment molecules to break down and rearrange. This rearrangement can lead to a change in color, often resulting in a reddish-brown hue. Additionally, the soap helps to emulsify and lift the oily components of the curry stain, aiding in its removal from the fabric.
Therefore, the combination of the alkalinity of the soap and the chemical properties of the turmeric pigment contribute to the reddish-brown color observed when scrubbing a curry stain with soap on white cloth.