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In: Chemistry

In a lab experiment; the objective is to titrate NaOH solution into known KHP solution to...

In a lab experiment; the objective is to titrate NaOH solution into known KHP solution to determine NaOH solution concentration. Using the same NaOH solution we titrate an UKNOWN sample of KHP. I am having trouble calculating the % purity of my sample.

mol of NaOH USED TO TITRATE IN ALIQUOT: 0.001289mol (trial 1), 0.001289mol (trial 2), 0.001291mol (trial 3)

mol of KHP in aliquot: I calculated as 1:1 ratio THEREFORE 0.001289mol (trial 1), 0.001289mol (trial 2), 0.001291mol (trial 3) - is this correct?

mol of KHP per mL: I calculated as 6.445*10^-5 (trial 1), 6.445*10^-5 (trial 2), 6.455*10^-5 (trial 3)

average moles of KHP per mL: trial 1 + trial 2 + trial 3 = answer / 3 = 6.448*10^-5 average moles KHP per mL.

total moles of KHP in volumetric flask: volumetric flask is 100mL: I calculated as 0.006448mol

PLEASE CHECK MY CALCULATIONS TO MAKE SURE I AM ON THE RIGHT TRACK.

NEXT IS ASKING FOR "MASS OF PURE KHP," does this mean g/mol? or does this mean the mass of pure KHP if it were 0.006448mol of it in the volumetric flask?

LAST IS ASKING FOR % PURITY OF MY SAMPLE. I AM UNABLE TO FIGURE OUT HOW EXACTLY TO CALCULATE THIS WITH MY GIVEN DATA.

Please show how to derive answer. If you need further information please comment, I will reply ASAP. I WILL RATE YOU FOR YOUR ASSISTANCE. THANK YOU!

Expert Solution

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Some data you are giving is not very clear. The relation mol to mol in the titration is in fact 1:1. But if you are titrating unknown solution of NAOH the number of mol that you obtain are from the KHP solution which you than can relate 1:1 to NAOH unknown solution. More frequently you weight the KHP standard with analytical balance and then titrate with the unknown NAOH solution. If you did this then you do have 0.001289mol (trial 1), 0.001289mol (trial 2), 0.001291mol (trial 3) of NAOH from the same number of mol of KHP in your trial. This number of mol you have to relate with the volume that you measured of NaOH (in the buret) so you can calculate the unknown concentration of NaOH solution:

This concentration, in turn will be used to determine the purity of the unknown KHP sample. In this part I don´t understand the data because it is exactly the same numbers as before. But I can tell you the procedure. You weight a sample of unknown KHP dissolve into an Erlenmeyer flask. Next you titrate with the NAOH solution you just evaluate. Again, the number of mol you obtain from the NaOH solution are exactly the number of mol of pure KHP in your sample. Let’s say you got 0.006448 mol for a sample you worked on a 100 ml Erlenmeyer flask. KHP MW = 204.22 g/mol

Pure grams of KHP = 0.006448 mol x 204.22 g/mol = 1.3154 g of KHP (mass of pure KHP)

To calculate the % of purity you need the real weight of the sample. This is not in the data of your problem but let’s say you weighed 1.5 g

% of purity = 1.3154 g /1.5 x 100 = 87.68 %

queen_honey_blossom answered 2 years ago

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