Why don’t we keep sour substances in brass and copper vessels?  Rain water conducts electricity but distilled water does not. Why?  Why do acids not show acidic behavior in the absence of water?   Why does a milkman add a small amount of baking soda to fresh milk to shift the pH of fresh milk from 6 to slightly alkaline?  Mention two uses of baking soda and washing soda.  (2 marks)