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Third level analytical chemistry

  • 26-04-2014 8:23pm
    #1
    Jennii.
    Closed Accounts Posts: 173 ✭✭


    Hey everybody,

    I'm having a tonne of trouble with analytical chemistry. I do not understand all the calculations involved to figure out how many moles in whatever and how to find the percentage of (say Aspiring/ Fe) in a sample. It's been 12 weeks and my exams are in 3, I really need to pass. I'm flying it otherwise and I appreciate I don't NEED it for exams but I really want to understand it..

    Can anyone help me? Just tips/ tricks/ sample answers/ bits of the whole calculation? Thank you in advance!


Comments

  • #2
    wishmaster200
    Registered Users, Registered Users 2 Posts: 54 ✭✭wishmaster200


    f**k anal ytical chemistry head down to empty pockets and get **** faced


  • #3
    Jennii.
    Closed Accounts Posts: 173 ✭✭Jennii.


    LOL, I wish :D Good answer though.


  • #4
    wishmaster200
    Registered Users, Registered Users 2 Posts: 54 ✭✭wishmaster200


    calculation involving amounts

    We use two units to describe how much of something we need to use: the gram and the mole. To these we add the prefixes of kilo-(103), milli-(10-3), micro-(10-6), and nano-(10-9). If you need to weigh something on the analytical balance, you will need the amount in grams. If you need to do a chemical calculation, the amount will almost always need to be in moles. To convert from one form to the other, just remember that

    the Gram Formula Weight (GFW) has units of grams/mole

    Example:
    You are told to weigh out 0.40 millimoles of MgSO4 to use in an EDTA titration. The GFW (found on the label of the reagent bottle) for the solid is 120.37 grams/mole. When solving problems, always write the units down.

    0.40 x 10-3 moles

    120.37 grams

    mole
    = 0.04815 grams
    Remember to check your calculation by cancelling out the units. To test yourself, convert the 0.04815 grams back into moles of magnesium sulfate.


  • #5
    Jennii.
    Closed Accounts Posts: 173 ✭✭Jennii.


    Wow, thank you :) And we're en route to understanding :D


  • #6
    wishmaster200
    Registered Users, Registered Users 2 Posts: 54 ✭✭wishmaster200


    calculations involving chemical reactions

    First you must have a balanced chemical reaction. Precipitation, acid-base, and complex formation reactions can be balanced by inspection. Oxidation-Reduction reactions are best balanced by the half-reaction method. All calculations are done with moles. If you are given amounts in grams, convert to moles first. If you are asked for grams, do the calculation with moles, then convert back to grams at the end. The chemical reaction tells you how to convert from moles of one chemical to moles of another.

    Example: How many grams of silver chromate can you get by complete precipitation of 0.1273 g of silver nitrate?

    2 AgNO3 + K2CrO4 = Ag2CrO4(s) + 2 KNO3
    0.1273 g AgNO3

    mole AgNO3
    1 mole Ag2CrO4
    331.73 g Ag2CrO4

    169.87 g AgNO3
    2 mole AgNO3
    mole Ag2CrO4
    = 0.1243 g Ag2CrO4


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