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Chemistry LibreTexts

5. Gold Nanoparticle Synthesis

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    1. Prepare 50 mL of 0.25 mM (millimolar) HAuCl4. A 2.5 mM stock solution is provided. What calculation do you need to perform to prepare the new solution? (Check with instructor!).
    2. Note the initial pH and Citrate to Auric Acid Ratio from the table below assigned to your group.
    3. Add your HAuCl4 solution to a 100 ml beaker with a magnetic stir bar and place it on a stir plate under mild stirring.
    4. Place a pH electrode in your solution, and add sufficient 0.02 M NaOH dropwise to achieve the desired pH. (What can you use to correct pH if you add too much NaOH? (Check with instructor!)

    Initial pH

    Citrate to Auric Acid Ratio






    Group 1

    Group 2

    Group 3


    Group 4

    Group 5

    Group 6


    Group 7

    Group 8


    1. Based on the 0.25 mM concentration of HAuCl4, how many moles of citrate will be needed to achieve the selected ratio? Perform the calculations and check with instructor! Now convert the number of moles into grams.
    2. Transfer your solution into a round bottom flask with a few boiling chips, place it in a heating mantle and connect it to a condenser column.
    3. Turn on the heating mantle to medium setting and bring the solution to gentle boiling, then add the calculated number of grams of sodium citrate to the solution.
    4. Continue boiling until the reaction is observed (an obvious color change will take place).
    5. Remove the solution from heat and allow it to cool back to room temperature (be careful of the hot glass).
    6. Once the solution is cooled, measure and record the final pH.
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