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    Please help with this question:
    3.88g of monoprotic acid was dissolved in water and the solution made up to 250cm3. 25cm3 of this solution was titrated with 0.095mol dm-3 NaOH solution, requiring 46.5cm3. Calculate the relative molecular mass of the acid.

    my attempt was:
    moles = (25/1000) x 0.095 mol dm3 = 2.38x10-3 moles
    molar mass = 3.88g/ 2.38x10-3 moles = 1634 Mr
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    (Original post by holderbolder)
    Please help with this question:
    3.88g of monoprotic acid was dissolved in water and the solution made up to 250cm3. 25cm3 of this solution was titrated with 0.095mol dm-3 NaOH solution, requiring 46.5cm3. Calculate the relative molecular mass of the acid.

    my attempt was:
    moles = (25/1000) x 0.095 mol dm3 = 2.38x10-3 moles
    molar mass = 3.88g/ 2.38x10-3 moles = 1634 Mr

    Take it a step at a time.
    -----------------------

    Moles of NaOH = molarity x volume (litres)

    Moles of acid = mol NaOH

    ... but this is in a 25 ml aliquot (sample of liquid)

    So, total moles of acid in 250 cm3 = mol NaOH x 10

    Relative mass = mass/moles = 3.88/(mol NaOH x 10)
    ------------------------------
    try again
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    Being a noob at this, lemme give it a try to see how good his instructions were

    Moles of NaOH = 0.095 mol dm-3 x (46.5/1000)

    = 0.0044175 mol

    Moles of HCL aliquot = Moles of NaOH

    however

    Moles of HCL aliquot (25cm3) x10 = Moles of HCL (250cm3)

    = 0.044175

    Relative molecular mass = 3.88g/0.044175mol

    = 87.8 (3sf)

    Rounded up to nearest integer = 88

    Hope I got that right
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    (Original post by kiLLthriLL)
    Being a noob at this, lemme give it a try to see how good his instructions were

    Moles of NaOH = 0.095 mol dm-3 x (46.5/1000)

    = 0.0044175 mol

    Moles of HCL aliquot = Moles of NaOH

    however

    Moles of HCL aliquot (25cm3) x10 = Moles of HCL (250cm3)

    = 0.044175

    Relative molecular mass = 3.88g/0.044175mol

    = 87.8 (3sf)

    Rounded up to nearest integer = 88

    Hope I got that right
    most certainly did :yep:
 
 
 
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