Why doesn’t the presence of other metal ions from the dissolved brass sample interfere with the quantitative analysis of copper in this experiment?*

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  • 1. Why doesn’t the presence of other metal ions from the dissolved brass sample interfere with the quantitative analysis of copper in this experiment?*
  • Select the number for the answer that best answers the question.
  • * 1. The presence of any other dissolved ions does not interfere with the quantitative copper determination because all of the other ions are not soluble.

2. The presence of other dissolved ions does not interfere with the quantitative copper determination because the other ions form red-colored species when oxidized.

3. The presence of other dissolved ions does not interfere with the quantitative copper determination because none of the other ions form a colored species when oxidized.

4. The presence of other dissolved ions does not interfere with the quantitative copper determination because they are soluble in the final aqueous solution.

  • 2. Is it necessary to filter the solution of the dissolved brass sample, but not the solution of the dissolved copper sample, before you take the respective absorbance readings?*
  • Select the number for the answer that* best answers* the question.
  • * 1. It is not necessary to filter the solution of the dissolved brass sample because all of the components that make up the alloy form soluble compounds when they are oxidized.

2. It is necessary to filter the solution of the dissolved brass sample because the alloy may contain other elements that form insoluble compounds, which will interfere with the light as it passes through the solution. Pure copper wire does not contain any such elements.

3. It is necessary to filter the solution of the dissolved brass sample because the copper ions react with other metal ions in solution to form insoluble compounds, which will interfere with the quantitative analysis of copper.

4. It is not necessary to filter the solution of the dissolved brass sample because all of the components that make up the alloy, except for copper, form insoluble compounds when they are oxidized.

  • 3. Suppose your unknown brass sample consists of a piece of hardware, such as a screw, and your lab is tasked with determining the copper content of the sample. One screw is not large enough to give a sufficiently concentrated solution of copper(II) ion when dissolved and diluted to 250 mL. Which of the following solutions would you choose to solve the problem?*

· *You dissolve two or more pieces of the same type and dilute to 250 mL.* · *You dissolve one piece, but dilute to a smaller volume.*

[FORM: http://www2.chem21labs.com/student2/?mode=assign&assignment=211]

  • Explain*.
  • 4. Suppose there is another species in the sample that absorbs at the same wavelength as copper. Will this cause your* *calculated* *copper concentrations to be /too high/ or /too low/? Explain why.*
  • Select “too high” or “too low”.*

[FORM: http://www2.chem21labs.com/student2/?mode=assign&assignment=211]

  • Explain*.
  • A piece of copper wire is 13.5 cm in length and has a mass of 1.3186 g. Calculate the concentration of each of the five stock solutions that would be prepared from this sample according to Table 1.*
  • Table 1 /Beer’s Law data/*
  • /Solution/*
  • /Initial mL of Sol. A/*
  • /Final mL of sol’n/*
  • /Final Molarity of Solution/*
  • A*
  • undiluted*
  • 250.00*
  • B*
  • 75.00*
  • 100.00*
  • C*
  • 50.00*
  • 100.00*
  • D*
  • 25.00*
  • 100.00*
  • E*
  • 10.00*
  • 100.00*
  • 6. It is becoming increasingly important for scientists to examine the entire process when they work with chemicals. As the costs for chemical waste and solvents increase, chemists are rethinking every step of the manufacturing process to select better raw materials to not only increase the efficiency of a reaction but also to reduce the amount and the toxicity of the waste products. With increased awareness of the environmental impact of various chemicals, this process becomes even more important. Allowed concentrations of copper ions in waste water per EPA regulations are being lowered, thus directly impacting our lab facility. We must now collect all aqueous copper solutions in waste bottles rather than pouring them down the drain.*
  • a. If 23 sections of 24 students each perform exp. 357 per the procedure in the lab manual, how much liquid waste (aqueous copper solution), in liters, will be generated? Students work in pairs and each student does his/her own unknown.*
* *
  • b. Suggest a way to significantly reduce the amount of waste.*
  • 7. Use the Internet to find the MSDS for NO and NO[2]. Prepare a summary of the hazards associated with exposure to NO and NO[2] as listed in the MSDS. Be sure to include required safety equipment in your summary.

That’s all the question.*

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