Chemistry lab

Can you help me understand this Chemistry question?

In the United States, Customs and Border Patrol agents often need to know the alcohol content of declared beverages being brought back into the country from abroad. Sometimes, beverages are labeled improperly. The United States Federal Alcohol Administration Act states that wines must contain an alcohol content within the range of 7-24%; below this value and above 0.5% is considered a beer and above 24% is considered to be a spirit. Of course, time is of the essence because of the shear volume of people passing through Customs. Thus, an easy way to do this rapidly is to calculate the density of the alcohol and compare it to known values.

In this laboratory experiment, you will be required to generate a set of known densities for alcohols with a certain percentage. Your ultimate task will be to determine classify two unknown alcohols based on their percent alcohol composition based on the following table:

Percent Alcohol Concentration

Classification

<0.5%

Non-alcoholic

0.5-7%

Beer

7-24%

Wine

>24%

Spirit

There are several learning objectives of this lab:

  • Practice computing the densities of unknown solutions volumetrically and gravimetrically.
  • Practice recording data and taking notes from experimental procedures.
  • Analyze data to make valid scientific conclusions.

The procedure below is but one way to perform the following lab experiment. As you work through the experiments, consider other ways that you may possibly carry out each step or even propose a new lab procedure in your report. Record any necessary notes and data in the pages that follow the procedure below. Write your report using the guidelines in the “Laboratory Information” section of the course’s home page.

Supplies:

Reagents:

  • Distilled water
  • 70% alcohol solution
  • Unknown alcohol solution A
  • Unknown alcohol solution B

Instruments

  • 250 mL beaker
  • 25 mL graduated cylinder
  • 100 mL volumetric flask
  • Balance

Procedure:

Pre-Lab Calculations (Record in ‘Notes’ section)

  • Compute the required volume of a 70% (v/v) stock solution of alcohol needed to produce 100 mL of a 0.5% (v/v) stock solution.
  • Compute the required volume of a 70% (v/v) stock solution of alcohol needed to produce 100 mL of a 7% (v/v) stock solution.
  • Compute the required volume of a 70% (v/v) stock solution of alcohol needed to produce 100 mL of a 24% (v/v) stock solution.
  • From the course home page, click on the Virtual Lab Tutorial link to watch the overview of using the virtual lab.
  • From the course home page, access the lab environment by clicking on the Virtual Lab link.
  • After the lab environment loads, click ‘File’ then ‘Load an Assignment.’
  • Select the ‘Molarity and Density’ category.
  • Select the ‘Alcohol Density Problem’ assignment.
  • At this point, you have prepared the laboratory with the require supplies to complete your experiments.

Preparing the Lab

Determine the Densities of Standards and Unknowns

  • Select the ‘Solutions’ tab if it is not already selected. You should now see four items including the distilled water and the three unknown metals. If not, verify that you have selected the correct assignment by following the steps in the “Preparing the Lab” section again.
  • Determine the density of a 0.5% alcohol solution:
  • Determine the density of a 7% alcohol solution:
  • Determine the density of a 24% alcohol solution:
  • Tare the mass of an empty 250 mL beaker and then label it as ‘Unknown A.’
  • Add an aliquot of Unknown A to the beaker and records its mass.
  • Compute the density of Unknown A using the volume and mass data.
  • Repeat Steps 5-7 for Unknown B.
  • Classify the unknowns using the table in the introduction of the lab.

a.Fill a 250 mL beaker with distilled water.

b.Transfer a 100 mL volumetric flask to the scale and then tare the scale.

c.Add the previously computed amount of the 70% stock alcohol solution to the graduated cylinder using the ‘Precise’ option for pouring. Transfer this amount to the volumetric flask.

d.Dilute the aliquot by using the ‘Precise’ option for pouring. Record the final mass of the solution.

e.Compute and record the density of the solution.

a.Fill a 250 mL beaker with distilled water.

b.Transfer a 100 mL volumetric flask to the scale and then tare the scale.

c.Add the previously computed amount of the 70% stock alcohol solution to the graduated cylinder using the ‘Precise’ option for pouring. Transfer this amount to the volumetric flask.

d.Dilute the aliquot by using the ‘Precise’ option for pouring. Record the final mass of the solution.

e.Compute and record the density of the solution.

a.Fill a 250 mL beaker with distilled water.

b.Transfer a 100 mL volumetric flask to the scale and then tare the scale.

c.Add the previously computed amount of the 70% stock alcohol solution to the graduated cylinder using the ‘Precise’ option for pouring. Transfer this amount to the volumetric flask.

d.Dilute the aliquot by using the ‘Precise’ option for pouring. Record the final mass of the solution.

e.Compute and record the density of the solution.

f.Clear the workbench.

Notes

This section should include notes about any observations or data collected during the lab.


Data

This section will include all data collected during the lab.

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