• Question: Why do alkalis clean better than acids? Why do the police use coke to clean away blood?

    Asked by 8hemy to MarkF, Mark, Michael, Panos, Sarah on 21 Jun 2010 in Categories: .
    • Photo: Sarah Burl

      Sarah Burl answered on 15 Jun 2010:

      Alkalies are good grease removers, because the alkalies form an emulsion, a mixture where oily or solid particles are held in suspension. The particles do not separate from the rest of the liquid; therefore, they are not redeposited on the surface being cleaned.
      Alkalies readily remove oily dirt. Alkaline cleaners also can remove oil from an oil-based paint, drying it and causing it to crack or peel.

      Acids are beneficial in removing hard-water deposits, discoloration from aluminum, brass, bronze, and copper and iron rust stains. Strong acids also eat away clothing, leather, and some metals. Very Mild — Vinegar is about 5 percent acetic acid and counteracts oven cleaners. Vinegar removes hard-water deposits from glassware. Lemon juice is a citric acid and works in much the same way as does vinegar.
      Coke is acidic but I haven’t heard of it being used to remove blood. Does it work?

    • Photo: Mark Travis

      Mark Travis answered on 15 Jun 2010:

      Ah, a chemistry question!! From what I can tell from looking this up on the internet, alkalis are better at cleaning grease and oily stains as they form an emulsion and keep the fat droplets from getting back on the surface being cleaned. Acids are better at cleaning things like metals.

      I had never heard of the police using coke to clean up blood (and my dad used to be, and my brother is a policeman!). I had a look on the internet, and this seems to be an urban myth….. Coke does contain phosphoric acid, and has been shown to clean things like pennies, and also to perhaps help with blood stains. But as for the police using it for blood stains? I don’t know…….

    • Photo: Panos Soultanas

      Panos Soultanas answered on 16 Jun 2010:

      Hi 8hemy,

      I am not really sure about this one. I think they foam better which somehow helps the cleaning process but I may be wrong on this one..

      I have not heard anywhere that police use coke to clean up blood. Is this true?

      🙁

    • Photo: Mark Fogg

      Mark Fogg answered on 16 Jun 2010:

      Isn’t the Coke business is an urban myth? 😉

      It really depends on what you are cleaning, acids are good for cleaning metals (coke and coins), alkalis in soap are good for removing grease (stains on clothes), by forming emulsions etc.

    • Photo: Michael Loughlin

      Michael Loughlin answered on 21 Jun 2010:

      I do not know..its triue as most detergents are alkaline and biological detergenst have to have microbial enzymes that will work in alkali conditions ( from salt plains and alkali lakes)
      I think alkali’s have a better action against fats and lipids but my chemfu is weak alas

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