The flask contains 25 mL of an unknown diprotic acid aqueous solution that react

Question

The flask contains 25 mL of an unknown diprotic acid aqueous solution that reacts in a 1:2 stochiometric ratio with NaOH. Titrate the solution with NaOH to determine the concentration of the acid.

Perform a titration by setting the concentration of the NaOH solution and adding it to the acid solution using the different Add Base buttons. The equilvalence point of the titration is passed when the indicator color changes.

The unknown sample can be titrated multiple times by pressing the Retitrate button and starting over.

Enter the concentration of the unknown acid solution.

To obtain accurate results, follow the following procedure:

switch the indicator to phenolphthalein

titrate 1 mL at a time until solution turns pink, make note of volume added

retitrate

add 1 mL at a time until 1 mL less than the first titration

add 0.05 mL at a time until the solution just turns pink

NaOH solution Add Base 1.00 mL 0.10 mL 0.05 mL Base Added 5.05 mL Experimental Settings Indicator O Methyl orange [NaOH] = 0.50 M Phenolphthalein Thymo!phthalein Set [NaOH], choose an indicator, and add base in increments using the buttons above. Retitrate Unknown acid solution 25 mL

Explanation / Answer

Titration data:

Volume of NaOH added = V(NaOH) = 5.05 ml

Molarity of NaOH = M(NaOH) = 0.50 M

Volume of acid taken = V(Acid) = 25 ml

Molarity of the acid = M

Now, since this is a diprotic acid:

Moles of NaOH added = 2 * Moles of acid

M(NaOH) * V(NaOH) = 2*(M * V(acid))

M = M(NaOH) *V(NaOH)/2*V(acid)

= 0.50 * 5.05/2*25

= 0.051 M

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