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  • Calculation questions - need urgent response

    What mass of dextrose (g) is contained in 89ml of a 0.914%w/v solution.

    0.425g of dextrose was dissolved in sufficient water to produce 233ml. What volume of the resulting solution would contain 2mmol of dextrose.
    3rd yr pharmacy student - bath

  • #2
    Re: Calculation questions - need urgent response

    please be more polite! a 'please' wouldn't go amiss!

    and sorry asterix, but it's too late on a friday night - my calculation brain (which is tiny and atrophied anyway) has gone to sleep. The best answer i can come up with for you at the moment is "duuurrrrr...."
    “It's not worth doing something unless you were doing something that someone, somewhere, would much rather you weren't doing.”

    Terry Pratchett

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    • #3
      Re: Calculation questions - need urgent response

      What answers do you get Asterix?

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      • #4
        Re: Calculation questions - need urgent response

        it confuses me when long time forum posters change their usernames. I can't remember who asterix is now. Apart from him being that little Gaulish guy....

        “It's not worth doing something unless you were doing something that someone, somewhere, would much rather you weren't doing.”

        Terry Pratchett

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        • #5
          Re: Calculation questions - need urgent response

          sorry in urgency , i forgot to say please. I apologise.

          I can't do them, hence I am asking people to show me how to do them from scratch.
          3rd yr pharmacy student - bath

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          • #6
            Re: Calculation questions - need urgent response

            Q. What mass of dextrose (g) is contained in 89ml of a 0.914%w/v solution.

            A. A 0.914%w/v solution contains 0.914g in 100ml so mass of dextrose in 89ml is 89/100 x 0.914g = 0.81346g


            Q. 0.425g of dextrose was dissolved in sufficient water to produce 233ml. What volume of the resulting solution would contain 2mmol of dextrose

            A. 1 mol of dextrose is 180g so 1mmol = 0.18g

            2mmol of dextrose is 0.36g so volume which contains 2mmol is

            0.36/0.425 x 233 = 197.365ml


            It's been a while since i've done this sort of calc. so if anyone else can confirm I would be grateful!!

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            • #7
              Re: Calculation questions - need urgent response

              I find the easiest method is to divide down to find out how much in 1ml and multiply up to 89ml. I get the same answer as JonF if by a slightly different route.

              We were taught by the C1V1 = C2V2 method which works - just remember conversion of units.

              If you got some time on your hands over the weekend take a look at he chapter on calculations in Pharmaceutical Practice by Winfield and Richards or the Pharmaceutical Press' Calculation textbooks these are the ones I used for my exams last year.
              wake up and smell the 1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione

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              • #8
                Re: Calculation questions - need urgent response

                Originally posted by JonF View Post


                Q. 0.425g of dextrose was dissolved in sufficient water to produce 233ml. What volume of the resulting solution would contain 2mmol of dextrose

                A. 1 mol of dextrose is 180g so 1mmol = 0.18g

                2mmol of dextrose is 0.36g so volume which contains 2mmol is

                0.36/0.425 x 233 = 197.365ml


                It's been a while since i've done this sort of calc. so if anyone else can confirm I would be grateful!!
                how do we know 1 mol is 180g?
                3rd yr pharmacy student - bath

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                • #9
                  Re: Calculation questions - need urgent response

                  Number of moles = mass(g)/Mr

                  Rearrange to get mass: Mass (g) = Number of moles x Mr


                  Therefore 1 mole of dextrose (Mr of 180) weighs 1x180 g or 180g
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                  ”We are real. We are not glam sh*t or anything else. We are Guns N’ Roses.”

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                  • #10
                    Re: Calculation questions - need urgent response

                    isnt this in the first module of A-level chemistry???? 180 is the molecular mass of dextrose, which implies one mole of dextrose would weight 180g.
                    We are the music makers, We are the dreamers of dreams and God damn we are that good

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                    • #11
                      Re: Calculation questions - need urgent response

                      Originally posted by SolomonQ View Post
                      isnt this in the first module of A-level chemistry???? 180 is the molecular mass of dextrose, which implies one mole of dextrose would weight 180g.
                      Anhydrous or monohydrate?
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                      How times change.

                      If you find you have read something that has upset or offended you an anyway please unread it at once.

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                      • #12
                        Re: Calculation questions - need urgent response

                        Would assume that dextrose would apply to item of commerce , ie monohydrate. However, if I were answering this question would give two answers just to show how superior I was to the examiner!
                        johnep

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                        • #13
                          Re: Calculation questions - need urgent response

                          A manufacturer needs to prepare 500 metronidazole suppositories in a fatty base, using a 2g mould. The amount of metronidazole in each suppository base must be 500mg. What is the total amount (in g) of base that is required. The displacement value of metronidazole is 1.7.


                          tried a very long method and got the wrong answer, anyone care to help
                          3rd yr pharmacy student - bath

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                          • #14
                            Re: Calculation questions - need urgent response

                            Again refer to the Pharmaceutical Practice book or the FASTRAK Pharmaceutical Compounding and Dispensing ... but basically the formula is:

                            Weight Base = (No of Suppository x Total Supposity Mass) - (Mass Drug / Displacement Value of Drug)

                            If I recall correctly?
                            wake up and smell the 1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione

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                            • #15
                              Re: Calculation questions - need urgent response

                              Originally posted by Asterix View Post
                              how do we know 1 mol is 180g?
                              Google!

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