Map Sapling Learning macmillan learning A chemist uses atomic absorption spectro

Question

Map Sapling Learning macmillan learning A chemist uses atomic absorption spectroscopy to measure the amount of calcium in a urine sample. When g the sample for analysis, the chemist adds an excess of La3 to the sample. Why is La added to the urine sample? O La3* promotes the formation of CaSO4(s) which is readily atomized in the flame La+ binds to PO43 in the urine sample which prevents the formation of Cas(PO4)2(s) and frees the Ca2 in the sample to be atomized. O La3* is added to the urine sample as a way of suppressing the ionization of Ca2 La3* binds to SO4 in the urine sample which prevents the formation of CaSO4(s) and frees the Ca2+ in the sample to be atomized. O La3* promotes the formation of Ca3(PO4)2(s) which is readily atomized in the flame O La produces a hotter flame which increases the amount of Ca2 that is atomized.

Explanation / Answer

Ans. Lanthanum (La3+) acts as a releasing agent that produces free Ca2+ from phosphate, sulfates and other compound/ complexes containing Ca2+. So, La3+ treatment minimizes the interferences by freeing Ca2+. Free Ca2+ can be better analyzed by AAS than when in compound or complex form.

Option A. Incorrect. The treatment releases Ca2+ from CaSO4.

Option B. Correct. Li3+ facilitates formation of Ca2+ by complexing itself with phosphate, sulfates, and other anions.

Option C. incorrect. It enhances ionization of Ca2+.

Option D. Correct. See #B.

Option E. Incorrect. It promotes dissociation of calcium phosphate to form Ca2+.

Option F. Incorrect. Amount of Ca2+ is NOT increased by La3+ in flame. It is increased because La3+ frees up Ca2+ from its compounds and complexes.   

So, correct options are: B, D

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