Case Study: The Golden Drain Conversation Transсrіpt. Boss: Please sit down, Fred. I understand that you have been preparing our gold(III) hydroxide. Is that correct? Fred: Yes, Ma’am. Is there a problem with the product? Boss: No, the product is fine but our supply of gold(III) chloride has run low. Fred: (nervously) Maybe that’s because I’m working harder than the last person in this position. Boss: (seriously) Maybe. Fred, please describe how you are making the gold(III) hydroxide. Fred: I mix the sodium hydroxide with the gold(III) chloride and our catalyst, then let it settle for about an hour and remove the clear liquid from the top. Then I centrifuge the sludge. I remove the rest of the liquid; finally, I let the material dry in the oven overnight. Boss: That’s not a very precise desсrіption. How much gold(III) chloride and how much sodium hydroxide do you mix? Fred: The first time I used 280.0 grams of gold(III) chloride and 12.0 grams of sodium hydroxide. Boss: Why did you use those amounts? Fred: Those were the numbers I remember from my first day of work. Boss: So, I’d expect you should have made about 200.0 grams of gold (III) hydroxide in this reaction. Fred: Well actually, I only got about 22.0 grams of gold(III) hydroxide. So, I increased the amount of all reagents by 10 times. Boss: (in a surprised voice) Everything? Fred: (nervously)Yes. Boss: Do you have a copy of the laboratory notebook for the reaction specification from your first day at work? Fred: (sheepishly) No, I don′t. It was easy to remember, so I didn′t write it down. Boss: (frowning) You must write down detailed notes on all reactions. Boss: So you added 2800.0 grams of gold(III) chloride and 120.0 grams of sodium hydroxide? Fred: That’s right, (pleased with himself) and I got about 232 grams of gold(III) hydroxide, which is significantly higher than 200 grams. Boss: And what happened to the liquid portion of each reaction? Fred: I dumped it down the drain; since I had already isolated the product. Boss: (heavy sigh) How many batches of product have you made? Fred: Five batches a week for a month. Boss: As you know gold (III) chloride is very expensive at about $112.00 per gram*. And you made 20 batches. This meeting is over. I have a suspicion that something is not right, but I don’t have the time to figure it out. I will hire ChemDetectives to investigate this matter. We will resume production only after we have their report. You may take the next 2 days as casual leave. Someone will get in touch with you after we have seen the report from ChemDetectives. *Sigma Aldrich 2021 Background: Table 1: molar mass of relevant compounds AuCl3(aq) + 3NaOH(aq) → Au(OH)3(s) + 3NaCl(aq) Equation 1 ANALYSIS QUESTIONS First Attempt 1. Which reagent is limiting (the limiting reagent is the one that is used up) in the first reaction? (Fred used 280.0 grams AuCl3 and 12.0 grams of NaOH) (SHOW YOUR WORK) 2. Based on the limiting reactant, what is the maximum number of grams of gold(III) hydroxide that can be made from the amounts that Fred mixed in the first reaction? (SHOW YOUR WORK) 3. Calculate the percent yield to show how the amount calculated in the previous question (theoretical yield) compares to the amount of gold (III) hydroxide that Fred actually made (as mentioned in the transсrіpt)? (SHOW YOUR WORK) 4. Calculate the percent yield again, but this time use Fred’s boss’s expected amount as the theoretical yield (see the transсrіpt for this value). (SHOW YOUR WORK). Second Attempt (after Fred increased everything by 10 times) 5. Which reagent is limiting in the second reaction? (Fred used 2800.0 grams AuCl3 and 120.0 grams of NaOH) (SHOW YOUR WORK) 6. In the previous question, what reagent was in excess? Calculate the amount of remaining excess reagent after the reaction goes to competition. Conclusions and Recommendations 7. What happened to the excess reagent? 8. Did Fred cause a loss to the company? If yes, calculate the loss caused to the company. HINT: first, calculate the total mass of gold (III) chloride (excess reagent) that was dumped down the drain (remember that he made 20 batches) and then multiply by the cost/gram. 9. Your service charge is 5% of the amount calculated in #3, how much did you earn for this investigation? 10. What is your recommendation about Fred to his employer?
