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Homework Help: Volume of stock solution

  1. Apr 24, 2014 #1
    1. The problem statement, all variables and given/known data
    Whats the stock solution volume required to prepare 100ml of a NaHCO3 solution 5g/L using a stock solution of NaHCO3 30g/L.

    2. Relevant equations

    M1*V1 = M2*V2

    M = Molarity = mols/L

    3. The attempt at a solution

    NaHCO3 = 84g/mol
    5g NaHCO3 = 0.0595238095238095mol
    30g NaHCO3 = 0.3571428571428571mol

    M1*V1 = M2*V2 => 0.0595238095238095*0.1 = 0.3571428571428571*V2
    V2 = 0.01666L = 16,7mL

    But the answer is 3,33 mL
  2. jcsd
  3. Apr 25, 2014 #2


    User Avatar

    Staff: Mentor

    16.7 mL is the right answer.

    Note: there is no need to convert everything to moles and molar concentrations. Answer doesn't depend on the identity of the substance. Final solution must contain 0.5 g (0.1L*5g/L), so you need to start with 0.5g/30g liters of the stock solution and dilute it to 100 mL.
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