Practical Analytical Chemistry (1) Faculty of Pharmacy Practical Analytical Chemistry (1) Department of Pharmaceutical Chemistry Practical (6)

Techniques and measurement purpose The purpose of this experiment is to understand the meaning and significance of the density of a substance. Theory Density is a basic physical property of a homogeneous substance; it is an intensive property, which means it depends only on the substance's composition and does not vary with size or amount. The determination of density is a nondestructive physical process for distinguishing one substance from another. Density is the ratio of a substance's mass to its own volume. m mass d = _____ = _________ V Volume

unit of density In the metric system the unit of density for a liquid or solid is measured in g/mL or g/cm3. The cm3 volume unit used with solids is numerically equal to mL volume unit used with liquids. That is, 1 mL = 1 cm3. In this experiment you will determine the density of several liquids and compare the physical properties of those liquids.

Procedure (Part 1) Density of water: In any chemistry experiment, it is always advisable to calibrate your instruments and to practice any new technique. The density of water can be found in the CRC Handbook of Physics and Chemistry. You will learn the technique for measuring the density of any liquid by experimentally determining the density of water then comparing it to the actual value obtained from the CRC Handbook. You will need to pay close attention to the proper use of a graduated cylinder and a balance. 1-Weigh a clean dry 50-mL graduated cylinder. 2-Remove it from balance and add 15.0 mL of distilled water and read the volume to the nearest 0.1 mL (carefully observe the bottom of the meniscus). 3-Re-weigh the graduated cylinder now containing water.

(Part 2) Density of methanol : Obtain some methanol. You will probably find the density of methanol in the CRC Handbook. Weigh a dry 50mL graduated cylinder. Remove it from balance and add 10 mL of methanol and read the volume to the nearest 0.1 mL (carefully observe the bottom of the meniscus). Re-weigh the graduated cylinder now containing methanol. Record the weight of methanol

This experimental error is also known as percent error and it describes the percentage the experimental value is off from the actual value. actual value - experimental value % error = _________________________ x 100 actual value

Points for discussion (Part 1): Density of water Look up the actual density of water: __________ What are the units? __________ 2. Weight of a dry 50mL graduated cylinder = ________________ 3. Volume of water added to graduated cylinder= ________________ 4. Weight of graduated cylinder and water. = ________________ 5. Mass of water in the graduated cylinder = ________________ 6. Calculate the density of the water using the equation, d = m/V. Show your work here: density = ________________ 7. Calculate your experimental error. = _________________

(Part 2): Density of methanol 1. Look up the actual density of methanol: _____________ 2. Weight of a dry 50mL graduated cylinder = ________________ 3.Volume ofalcohol added to graduated cylinder= ________________ 4. Weight of graduated cylinder and methanol.= ________________ 5. Mass of methanol= ________________ 6. Calculate the density of the methanol using the equation, d = m/V. Show your work here: density= ________________ 7. Calculate your experimental error. = _________________