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  • Sodium chloride dilution

    I am writing an account on how to make a 0.45% solution of 500mls from a stock solution of 0.9%. I am a bit unsure of the help my pharmacist gave me. It's measure 250mls of stock solution and then add 250mls of purified water straight.
    I originally had 500mls of stock but am I right in thinking that this may not be the way it should be properly made up?!
    Any ideas on what literature I can have a look at for the formula and expiry? I have no books in the pharmacy to help me out!

  • #2
    Sounds ok to me.

    It looks like your pharmacist thinks of it from a practical perspective. If you're halving the concentration, you double the dilution.

    Another way to explain is in pure w/v.

    You have 500ml 0.9g/100ml solution.

    Therefore 4.5g/500ml

    You want 0.45g/100ml. So 2.25g/500ml.

    So you need half of your original solution to have 2.25g total then dilute it up to 500ml.

    Apologies if this doesn't entirely make sense as I'm trying to verbalise my thought process.
    I remember when a blog was an individual boot.

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    • #3
      Edit:

      Apologies I just realised this wasn't for a registration exam.

      The BP may have expiry dates?
      I remember when a blog was an individual boot.

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      • #4
        Your pharmacist is right.

        your original solution is 0.9%

        you want a 0.45% solution. 0.9 divided in half is 0.45, so your stock solution is TWICE as strong as what you want to make, so you need to dilute it by half.

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