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Module 1: Técnicas espectroscópicas

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Técnicas espectroscópicas - actividad 5

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XSIQ
*

Chemistry - Spectroscopic techniques - activity 5

Spectroscopic techniques - activity 5

The nickel content of a sample of iron ore was determined by atomic
absorption spectroscopy. A 1.000 g sample of the iron ore was dissolved in
20 mL of concentrated hydrochloric acid and the solution diluted to 100.0
mL in a volumetric flask.

In order to obtain a calibration curve relating absorbance and the
concentration of nickel, a number of standards of known nickel
concentration were prepared. The absorbance of each standard and the
prepared iron ore solution were determined using the sample instrument
conditions.

The following experimental data were recorded.

STANDARDS
ABSORBANCE

blank 0 mg L-1 NIL
0.0009

1. 50.0 mg L-1 NIL
0.2711

2. 100.0 mg L-1 NIL
0.5255

3. 150.0 mg L-1 NIL
0.7038

4. 200.0 mg L-1 NIL
0.8850

ORE SAMPLES

Sample 1
0.6580

Sample 2
0.6570

(a) Use the experimental data to construct a calibration curve showing the
relationship between absorbance and the concentration of nickel.

(b) Use the calibration curve to determine the concentration of nickel in
the iron ore solution.

(c) Determine the percentage, by mass, of nickel in the iron ore.

(d) The experimental data show that the blank solution, which has no added
nickel, does absorb a small amount of the incident light. Given that the
wavelengths selected are only absorbed by nickel atoms, why does the blank
register an absorbance?

Common uses of AAS include:

* mining and metallurgy: for quality control of alloys, steels etc and
monitoring metal levels in effluent going into waterways

* food analysis: high metal levels can be toxic to people and cause 'off'
tastes

* pharmaceuticals: to determine metal content of drugs, vitamins etc.

Answer - part a

Answer - parts b - d

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