Pagel PRELAB QUESTIONS 1. Identify the @rna e i OHK1 NAME: five possible anions

Question

Pagel PRELAB QUESTIONS 1. Identify the @rna e i OHK1 NAME: five possible anions which are to be identified in this experiment ura,3o, naro, Hnue 2. How many of these five anions will appear in your unknown sample? cnly ore : noel 3. Four of the chemicals used to make the known How will this affect your results in this experiment? and unknown samples contain the sodium ion. 4. What purpose does the centrifuge have in this experiment? Sepvele tons om ore ondl 5. Four of positive tests for an unknown ion involve the formation of a precipitate. Which lon has a positive test that involves the formation of gas?

Explanation / Answer

Qualitative analysis of anions

1. Possible anions to be identified in this experiment would be,

Cl-, Br-, I-, SO4^2- and CO3^2- ions

2. In the unknown we expect to see only one anion of the five possible anions suggested in 1.

3. The chemicals used to prepare the known and the unknown contains sodium in it. Analysis of sodium is done separately. However, in the anion analysis we would not see any interference of the sodium present in the solution.

4. Centrifugation is done to separate the precipitate from the supernatant liquid.

5. CO3^2- ion forms CO2 gas and is a positive test for this anion in the experiment.

6. When an unknown sample was analyzed by the student with AgNO3 it gave a white precipitate. The precipitate formed would be of AgCl,

AgNO3 + Cl- ----> AgCl (white ppt) + NO3-

When ammonia is added to the precipitate, it dissolved as it forms a complex which is soluble

AgCl (ppt) + 2NH3 ----> [Ag(NH3)2]Cl (soluble)

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