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In an experiment, 13.88 g of potassium propionate, C2H5CO2K, were weighed in a beaker and dissolved in a small amount of distilled water. The mixture is transferred to a 100 mL volumetric flask, made up to the mark and shaken well. 50.0 mL of this standard solution is mixed with 50.0 mL of a standard solution of propionic acid, C2H5CO2H in order to prepare a buffer solution of pH 5.66. The molar mass of potassium propionate is 112 g mol-1 and the pKa of propionic acid is 4.87. (i) What is the concentration of the propionic acid used to make the buffer?  5.0 mL of 5.0 M nitric acid were added to 100.0 mL of the buffer. (ii) Give a chemical equation to show the effect of nitric acid on the buffer. (iii) Calculate the new concentration of the propionic acid in the mixture.

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Related questions

"A 0.1852-g sample of steel wasdissolved in dilute nitric acid, treated with ammoniumperoxidisulfate, transferred to a 50-mL volumetric flask, anddiluted to the mark with distilled water. Two 10.00 mL aliquots ofthe resulting unknown solution were placed in separate beakers towhich were added 5 mL of concentrated phosphoric acid and 0.40grams of potassium periodate. After the manganese was oxidized topermanganate, 5.00 mL of a standard potassium permanganate solutioncontaining 20.0 ppm Mn, was added to one of the beakers. Theresulting solutions were transferred to 50.0-mL volumetric flasksand diluted to the mark with distilled water. The absorbance of thesolutions were determined to be 0.118 and 0.327 at 525 nm.Calculate the %Mn in the steel."


This question is from an old exam,and included with this question was the answer key. The instructorcalculated the concentration of the solution to be 1.13 ppm, whileI calculated it to be x = 2.82 ppm. Did I do something wrong, ordid the instructor make a mistake? I'd hate to miss a similarquestion on my next exam simply because I missedsomething...thanks!

18. You are asked to prepare 500. mL of a 0.100 M acetate buffer at pH 5.10 using only pure acetic acid (MW=60.05 g/mol, pKa=4.76), 3.00 M NaOH, and water. Answer the following questions regarding the preparation of the buffer.

1. How many grams of acetic acid will you need to prepare the 500 mL buffer? Note that the given concentration of acetate refers to the concentration of all acetate species in solution.

2. What volume of 3.00 M NaOH must you add to the acetic acid to achieve a buffer with a pH of 5.10 at a final volume of 500 mL? (Ignore activity coefficients.)

3. Pour the beaker contents into a 500 mL volumetric flask. Rinse the beaker several times and add the rinses to the flask. Swirl the flask to mix the solution. Add water to the mark to make the volume 500 mL. Stopper the flask and invert how many times to ensure complete mixing? 1,2, or 20?

PHOSPHATE STANDARD CALCULATION HELP

Have one correct answer, stuck on where to go from ther. Urgent request, please help

1) Diluting Concentrated Nitric Acid
Calculate the volume of 15 M Nitric acid required to make 300 mL of 1.1 M nitric acid.

a) Volume of 15 M Nitric acid required _____22.0_________ mL

2) Making the Original Phosphate Solution
You weigh out pure NaH2PO4.

Weight of Sodium Dihydrogen phosphate used 0.4567 g

This is dissolved, quantitatively transfered, and diluted to 100 mL in a volumetric flask.
10 mL of this is pipetted and again diluted to 100.00 mL to make the original phosphate standard.
Calculate:

b) The phosphate concentration of this solution ______________ mM

3) Making a Standard for Measurement in the Spectrometer

Volume of original phosphate standard (problem 2) used 2.50 mL

The phosphate standard, 5 mL of molybdate solution and 10 mL of dilute Nitric acid were added to a 100 mL volumetric flask, diluted to volume and mixed thoroughly.
Calculate:

c) Phosphate concentration in this standard _______________ mM

4) Measuring the Absorbance of the Standard
The solution in 3) was put in a cuvet and the %T measured at 380 nm.

% T of solution 48.0 %
% T of blank 96.1 %

Calculate:

d) Absorbance of standard _______________

5) Analysis of an Unknown
This is a separate problem and does not depend on 1, 2, 3, or 4.
3.51 mL of "Unknown Solution" were pipetted into a 100 mL volumetric flask along with the molybdate and nitric acid solutions. This was diluted to volume, mixed and measured in the spectrometer.

The absorbance of this solution was 0.223
The concentration of this solution (from standard plot) was 0.0070 mM

Calculate:

e) Concentration of the unknown solution _______________ mM
f) Concentration of the unknown solution _______________ ppm P
g) Grams of "H3PO4" in 450 mL of unknown _______________ g

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