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    Twain2009's Avatar
    Twain2009 Posts: 1, Reputation: 1
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    #1

    Mar 16, 2009, 12:24 PM
    lab work
    1. Prepare the NaOH solution by dissolving approximately 4g of solid NaOH in 200 mL of water. Calculate and record the approximate NaOH concentration (MW = 40.00).
    2. To prepare the primary standard, first calculate and record the expected mass of benzoic acid required to react in stoichiometric proportion with 20 mL of the NaOH solution (MW = 122.12). Record this amount.
    Perito's Avatar
    Perito Posts: 3,139, Reputation: 150
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    #2

    Mar 16, 2009, 08:54 PM

    1. Figure out the molecular weight (formula weight) of NaOH. You have 4 grams of NaOH. The molecular weight is in grams/mole so if you divide grams by grams/mole, you'll end up with moles. It's approximate because NaOH absorbs water and CO2 from the air and the weight is approximate -- not accurate.

    2. From #1, you know the approximate number of moles. Benzoic acid has only one hydrogen ion to react with the NaOH, so 1 mole reacts with 1 mole (I'll let you write down the equation and balance it). You have the number of moles from #1 so divide that by the 200 mL of solution to get moles/mL. Since you now know the number of moles you'll need, divide that by moles/mL to get mL.

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