You measure 2.99 mL of a 50% NaOH solution by weight (its density is 1.53 g mL-1) and dilute it to 500 mL total volume. ?

You measure 2.99 mL of a 50% NaOH solution by weight (its density is 1.53 g mL-1) and dilute it to 500 mL total volume. What is the concentration of this NaOH solution? Write your answer to four decimal places

Can someone help me figure this out 

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  • Anonymous
    4 weeks ago

    Normally I would use the standard dilution equation, C1 * V1 = C2 * V2 but I don't think that's applicable because the density of the solution will change a lot.  I'll do it two ways.

    50% * 2.99 mL = C2 * 500 mL.  C2 = 0.299 wt%.

    Second check

    2.99 mL of 50% caustic = 4.575 g (volume * density).  50% of this is NaOH so 2.2874 g NaOH.

     

    2.2874 g / 500 mL = 0.5 m/v %.  This isn't the same basis as a pure wt% basis but it shows me the diluted solution is pretty much water (which is not true for the 50% solution) so I'm willing to assume the density of the diluted solution is the same as  water (you can look up densities of NaOH solutions but I don't need to). 

    500 mL of a solution with a density similar/equal to water = 500 g.

    mass % NaOH = 2.2874 g / 500 g * 100 = 0.46 wt%  Significantly greater than the 0.299% I got using the simple dilution formula which I suspected might be the case.

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