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Question 1 of 3

Strong Cetrimide Solution BP 1988 comes as a 40 % w/v solution. How many millilitres of this solution do you need to prepare 500 millilitres of 1 in 100 solution? Answer to 1 decimal place.

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millilitres
You need 12.5 ml of Strong Cetrimide Solution BP.
  1. Express the concentration needed as a percent weight in volume.
    1 in 100 means that 100 ml of solution contains 1 g of Cetrimide.
    Thus the concentration needed is 1 g/100 ml ie 1 % w/v.
  2. Find the volume of Strong Cetrimide needed by using the equation:
    Concentration1 x Quantity1 = Concentration2 x Quantity2
            40        x Quantity1 =                 1           x   500
    Quantity1 =   500   ml
    40
    Quantity1 = 12.5 ml
    You need 12.5 ml of the Strong Cetrimide Solution.
    Formula:
    12.5 ml Strong Cetrimide Solution BP to      500 ml Water

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Question 2 of 3

Potassium Permanganate is supplied as a solution with concentration 1 in 1000. How many millilitres of this solution do you need to prepare 750 ml of a 0.0125 % solution of Potassium Permanganate? Answer to 2 decimal places.

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millilitres
You need 93.75 ml of the stock Potassium Permanganate solution.
  1. Express the concentration of the supplied solution as a percent weight in volume.
    1 in 1000 means that 1000 ml of solution contains 1 g of Potassium Permanganate.
    Thus 100 ml of solution contains 0.1 g of Potassium Permanganate.
    Thus the concentration of the supplied solution is 0.1 g/100 ml ie 0.1 % w/v.
  2. Find the volume of 0.1 % Potassium Permanganate needed by using the equation:
    Concentration1 x Quantity1 = Concentration2 x Quantity2
              0.1       x Quantity1 =           0.0125     x       750
    Quantity1 =   9.375   ml
    0.1
    Quantity1 = 93.75 ml
    You need 93.5 ml of the stock solution of Potassium Permanganate.

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Question 3 of 3

You need to prepare 300 ml of a 10 % solution of Formalin. How much Formaldehyde Solution BP (34-38 %, density 1.08 g/ml) do you need?

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ml
You need 30 ml of Formaldehyde Solution BP.
  1. A 10 % solution of Formalin is the same as a 10 % v/v solution of Formaldehyde
    Solution BP 1988.
  2. Find the volume of Formaldehyde Solution needed.
    Concentration1 x Quantity1 = Concentration2 x Quantity2
    Since you are diluting Formaldeyde Solution BP itself, Concentration1 is 100 %.
       100           x Quantity1 =           10           x      300
    Quantity1 =   3000   ml
    100
    Quantity1 = 30 ml
    Formula:
    30 ml   Formaldehyde Solution BP to      300 ml Water

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