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rubyserval482Lv1

6 Nov 2019

An unknown sample of Cu2+ gave an absorbance of 0.263 in an atomic absorption analysis. Then, 1.00 mL of solution containing 133.00 ppm Cu2+ was mixed with 91.00 mL of unknown, and the mixture was diluted to 100.00 mL in a volumetric flask. The absorbance of the new solution was 0.490. Find [Cu2+] (ppm units) in the unknown.

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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

A calibration curve was created using a solution made up of 0.08 g Pb(NO₃)₂ diluted in a 500 mL volumetric flask with 0.28% HNO₃ solution. Dilutions were made at 2.5, 5.0, 7.5, and 10.0 ppm to generate the curve. A 0.5 g brass sample was prepared by adding 5 mL HNO₃ and 5 mL HCl, then diluted with 0.28% HNO₃ solution in a 100 mL volumetric flask. A 3:200, 2:100, and 5:200 dilute solution was made (using 0.28% HNO₃) from the unknown sample and placed in a 100 mL volumetric flask. From the data below, what is the % Pb in the unknown brass sample?