CHE 110: PRACTICAL INTRODUCTORY ORGANIC CHEMISTRY QUESTIONS AND ANSWERS

 PROBLEM

1. give Four safety rule to be observed when working in a chemistry

Laboratory.

2. List the apparel that constitute an appropriate clothing for chemistry laboartory?

3. How would you dispose of the following waste when working in a chemical

environment

a) Glass waste

b) Liquid and solid waste

c) Chemical spillage

d) Used filter paper

4. a)As a young chemist, you have been provided with an impure benzoic acid. Your

benzoic acid looks brownish in color with other contaminants. Pure benzoic acid looks

white crystalline solid. Outline seven basic steps in employing the method of

crystallization to help purify the benzoic acid.

b) Mention TWO(2) ways you can ascertain the purity of your recrystallized benzoic

acid.

C) Would you achieve a 100% recovery of the recrystallized benzoio acid? Give reasons

for your response.

d) Asantewaa a chemistry student at the University of Cape Coast determined the

melting point of Compound A to be 65°C- 66°C whilst her research team member

Addo, also a chemistry student at the Kwame Nkrumah University of Science

Technology determined the melting point of another compound B to be 65°C- 66°C.

I) Are the two compounds A&B the same?

II) Describe a method to justify whether the two compounds are the same or not.

III) Melting point measurement provides two pieces of information about a sample of a solid organic compound. What are they?

iv) Why is it necessary to carry out melting point on a finely powdered solid sample?

                                                  SOLUTION TO PROBLEM 1

1. Four safety rules to be observed when working in a chemistry laboratory:

   a) Always wear proper personal protective equipment (PPE), including safety goggles, gloves, and a lab coat.

   b) Never eat, drink, or smoke inside the laboratory to prevent contamination.

   c) Be familiar with the locations of safety equipment such as fire extinguishers, eyewash stations, and safety showers.

   d) Properly label and store chemicals, and make sure to follow proper procedures for the handling and disposal of hazardous materials.

2. Appropriate clothing for a chemistry laboratory includes:

   a) Closed-toe shoes to protect feet from spills and dropped objects.

   b) Long pants or a long skirt to protect legs from spills.

   c) A well-fitting lab coat or apron to protect clothing and skin.

   d) Safety goggles to protect eyes from chemical splashes and flying debris.

3. Disposal of waste in a chemical environment:

   a) Glass waste: Dispose of broken glass and other sharp objects in a designated glass waste container.

   b) Liquid and solid waste: Dispose of hazardous liquid and solid waste in appropriate containers following laboratory guidelines and regulations.

   c) Chemical spillage: Clean up spills immediately using proper safety equipment and techniques, and dispose of used materials in designated waste containers.

   d) Used filter paper: Place contaminated filter paper in the appropriate hazardous waste container based on the chemicals it was used with.

4. a) Seven basic steps for purifying impure benzoic acid using crystallization:

   i) Choose a suitable solvent for dissolving impure benzoic acid.

   ii) Heat the solvent to dissolve the benzoic acid.

   iii) Filter the hot solution to remove insoluble impurities.

   iv) Allow the filtered hot solution to cool slowly, enabling benzoic acid to form crystals.

   v) Filter the crystals to separate them from the remaining liquid.

   vi) Wash the crystals with a small amount of cold solvent to remove residual impurities.

   vii) Allow the crystals to dry, obtaining purified benzoic acid.

   b) Two ways to evaluate the purity of recrystallized benzoic acid:

   i) Determine its melting point and compare it to the known melting point of pure benzoic acid.

   ii) Perform a colorimetric analysis to assess the color of the purified crystals.

   c) 100% recovery of recrystallized benzoic acid is unlikely due to losses during the crystallization process, such as incomplete dissolution, removal of impurities, or during filtration and drying.

   d) Melting point analysis questions:

   i) Compounds A and B might be the same based on their melting points, but further analysis is required to confirm their identity.

   ii) A method for comparison is through mixed melting point analysis, in which small amounts of the two compounds are mixed together and the melting point is redetermined. If the melting point remains unchanged, the compounds are likely the same. If the melting point is lowered or broadened, the compounds are different.

   iii) Melting point measurement provides information about the compound's purity and its identity (by comparing it to known data).

   iv) It is necessary to carry out melting point measurements on finely powdered solid samples because it ensures uniform and consistent melting, allowing for accurate and consistent measurements.