ANAL 503: Nine Bottles: An Adventure in Chemical Identification Post-Laboratory

Question

ANAL 503: Nine Bottles: An Adventure in Chemical Identification Post-Laboratory Questions Use the spaces provided for the answers and additional paper it necessary, or write the answers in your laboratory notebook.) 1. State one or more reasons why it is necessary to 3. When performing this esxperiment, some students use clean pipets for this experiment tend to do less pre-laboratory preparation than others. What useful advice would you give to a student who has been asked to perform this experiment a few weeks from now? Defend or refute each of the following statements. (1) When reasonably dilute HCI and AgNOs so- lutions are mibxed, a white AgCI precipitate forms, with some heat evolving. When a Na2S203 solution is added to this reaction mixture, the white precipitate 2. disappears upon stirring. 4. Some of the reaction types occurring when al possible pairs of the nine solutions are mbed Include oxidation-reduction, hydrolysis, and acid-base. When a confirming solution is added to a mixed pair, possible reaction types include common-ion effect and complex formation. Which of these types did you observe dur- ing your identification of your nine unknown solutions? Did you observe any reactions types not listed here? (2) Some chemists say that the AgCl in (1) dis- solves. Others say that AgCl is prevented from precipi- tating further by the presence of S20,2 ion. date section

Explanation / Answer

Answer

1. Titrations are performed to find out the concentration of the chemical in the sample. So we should use the clean pipettes for that. Otherwise, the concentration of the chemical will be affected. There is a chance of adding impurities to the sample. This may affect the concentration of the chemical in the sample.  

2. 1. Yes. AgCl is prevented from precipitating further by adding sodiumthiosulfate.

2. It may be due to the formation of complex ion with thiosulfate.

3. Before performing an experiment, a student must performing the pre-laboratory preparation. Then only student will understand the concepts of the reactions and also about safety precautions if needed.

4. Most of the titrations involve neutralisation reactions, redox reactions and complex formation reactions.

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