Question 1

What personal protective equipment is required before starting a melting point lab?

Accepted Answer

Before beginning a melting point experiment, wear a lab coat, chemical splash goggles, and gloves to protect yourself from potential hazards. These items are essential safety requirements for all students conducting this laboratory procedure. Ensure all equipment is properly fitted and in good condition before starting work.

Question 2

How do you prepare the urea and benzoic acid mixture for a melting point determination?

Accepted Answer

Prepare a mixture by combining urea and benzoic acid in a 4-to-1 mass ratio. Measure 0.48 g of urea using a tared weighing boat, then transfer it to a glass vial with a powder funnel. Add 0.12 g of benzoic acid to the vial and mix thoroughly by stirring with a spatula and shaking the closed vial.

Question 3

What is the purpose of the mineral oil bath in melting point experiments?

Accepted Answer

The mineral oil bath serves as a heating medium to uniformly heat samples during melting point determination. Approximately 150 mL of mineral oil is poured into a 250-mL beaker for each group. The oil provides consistent temperature control and allows accurate observation of sample melting behavior.

Question 4

What equipment should be set up at each student workstation for a melting point lab?

Accepted Answer

Each student pair requires a stir bar, stirring hotplate, lab stand, thermometer clamp, pre-calibrated digital thermometer (60–150°C), four melting point capillary tubes, three metal spatulas, three watch glasses, and a rubber band. These items enable students to safely heat samples and accurately measure melting temperatures during the experiment.

Question 5

How should the urea and benzoic acid mixture be labeled and stored before the lab?

Accepted Answer

Label the vial containing the mixed urea and benzoic acid as 'urea with unknown' before distributing it to student workstations. Store the labeled vial near the balance along with pure urea, naphthalene samples, and a designated solid waste beaker. This organization ensures students can quickly access materials at the start of the experiment.

Question 6

What quantity of naphthalene should be prepared for each student group?

Accepted Answer

Prepare approximately 1 mg of naphthalene for each student group conducting the melting point experiment. Obtain enough naphthalene in advance and store it near the balance with other prepared materials. This small quantity is sufficient for students to use during their melting point determination procedure.

Question 7

Why is a section of glass tubing placed on a communal bench during lab preparation?

Accepted Answer

A 2-foot section of glass tubing is set on a communal bench for students to access and use during the melting point experiment. This shared resource allows all student groups to utilize the same equipment without requiring individual tubes at each workstation, promoting efficient lab organization and resource management.

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