Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

Physical Properties Experiment: Determining the Identity of Unknown Organic Compounds, Lecture notes of Organic Chemistry

An experiment aimed at determining the physical properties of unknown organic compounds, including their solubility, density, melting point, boiling point, and refractive index. The experiment involves using various solvents and techniques to measure these properties, which can help identify and determine the purity of the compounds. The document also includes a list of possible solids and their solubility in different solvents, as well as a procedure for conducting the experiment.

What you will learn

  • What physical properties are measured in this experiment?
  • What techniques are used to measure the melting point and boiling point of a substance?
  • How can the solubility of a substance be determined?

Typology: Lecture notes

2021/2022

Uploaded on 09/12/2022

hardcover
hardcover 🇺🇸

4.7

(7)

259 documents

1 / 5

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Experiment 1: Physical Properties of Organic Compounds
Introduction
Physical properties are defined as a property that can be measured without changing the
composition of the substance. The physical properties that will be measured during this
lab are solubility, density, melting point, boiling point and refractive index. These
physical properties can help elucidate the identity of an unknown substance. These same
properties can also be used to determine the purity of a particular compound. Let us look
at each of these properties individually.
Solubility is defined as the maximum mass of a substance that can be dissolved in a fixed
mass of a solvent at a given temperature. A substance will have a different solubility in
different solvents depending on polarity of both the substance and the solvent. The old
adage is that like dissolves like, hence a polar substance will be more soluble in a polar
solvent and vice versa. The solvents used in this experiment will be water, ethanol,
acetone and benzene.
Density is defined as the mass of a substance per a unit volume. In this experiment,
grams per milliliter will be the density units. A dense liquid such as mercury has a
density of 13.546 g/mL. In contrast, hexane has a density of only 0.659 g/mL. Hence,
one can use the density in determining the identity of an unknown substance.
The melting point is defined as the temperature at which a substance goes from a solid to
a liquid. For example, water (ice) changes from a solid to a liquid at 0 Celsius at STP.
Although the melting point is usually listed at a certain temperature, most substances melt
over a temperature range. The temperature range is defined as the temperature at which a
substance begins to melt to the temperature at which the whole sample is completely a
liquid. A smaller temperature range would indicate a purer substance.
The boiling point is defined as the temperature at which a substance goes from a liquid to
a gas. For example, water changes to steam at 100 Celsius at STP. However, unlike the
melting point, boiling points are significantly affected by atmospheric pressure.
The refractive index can also be used to determine the identity of an unknown substance.
Refraction is the changing in the direction of a ray of light passing from one medium to
another. You have probably observed this looking down into the water while standing in
it. The refraction of light causes you legs to look shorter. As with the other physical
properties, a substance has unique refractive index.
pf3
pf4
pf5

Partial preview of the text

Download Physical Properties Experiment: Determining the Identity of Unknown Organic Compounds and more Lecture notes Organic Chemistry in PDF only on Docsity!

Experiment 1: Physical Properties of Organic Compounds

Introduction

Physical properties are defined as a property that can be measured without changing the composition of the substance. The physical properties that will be measured during this lab are solubility, density, melting point, boiling point and refractive index. These physical properties can help elucidate the identity of an unknown substance. These same properties can also be used to determine the purity of a particular compound. Let us look at each of these properties individually.

Solubility is defined as the maximum mass of a substance that can be dissolved in a fixed mass of a solvent at a given temperature. A substance will have a different solubility in different solvents depending on polarity of both the substance and the solvent. The old adage is that like dissolves like, hence a polar substance will be more soluble in a polar solvent and vice versa. The solvents used in this experiment will be water, ethanol, acetone and benzene.

Density is defined as the mass of a substance per a unit volume. In this experiment, grams per milliliter will be the density units. A dense liquid such as mercury has a density of 13.546 g/mL. In contrast, hexane has a density of only 0.659 g/mL. Hence, one can use the density in determining the identity of an unknown substance.

The melting point is defined as the temperature at which a substance goes from a solid to a liquid. For example, water (ice) changes from a solid to a liquid at 0 Celsius at STP. Although the melting point is usually listed at a certain temperature, most substances melt over a temperature range. The temperature range is defined as the temperature at which a substance begins to melt to the temperature at which the whole sample is completely a liquid. A smaller temperature range would indicate a purer substance.

The boiling point is defined as the temperature at which a substance goes from a liquid to a gas. For example, water changes to steam at 100 Celsius at STP. However, unlike the melting point, boiling points are significantly affected by atmospheric pressure.

The refractive index can also be used to determine the identity of an unknown substance. Refraction is the changing in the direction of a ray of light passing from one medium to another. You have probably observed this looking down into the water while standing in it. The refraction of light causes you legs to look shorter. As with the other physical properties, a substance has unique refractive index.

List of possible solids and their solubility in certain solvents

Compound Water Ethanol Acetone Benzene

Acetamide soluble soluble Acetanilide soluble soluble soluble Anthracene soluble^ soluble Benzoic Acid soluble soluble soluble Benzoin soluble soluble

List of possible liquids 1-propanol 2-propanol 2-butanol 2-methyl-1-propanol 3-methyl-1-butanol ethyl acetate toluene

Procedure

Melting Point

Determine the melting point of your unknown solid

  1. Deposit approximately 0.01 grams of your unknown solid into a small pile on a piece of weigh paper.
  2. Insert a capillary tube, open end down, into the pile of unknown solid forcing some of the solid into the capillary tube.
  3. Tap your capillary tube, closed end down, on the bench top to force the solid to the bottom of the capillary tube.
  4. Repeat steps 2 and 3 until approximately 5 mm of sample are at the bottom of the capillary tube.
  5. Place your capillary tube, closed end down, into the melting point apparatus.
  6. Turn on the melting point apparatus and watch both the temperature display and your solid sample. (Heating your sample too quickly will result in an inaccurate melting point determination.)
  7. When your sample begins to melt, record the temperature.
  8. As soon as the entire sample is melted, once again record the temperature, this will give you the temperature range.
  9. Repeat steps 1 through 8 to confirm your melting point.

Solubility Determine the solubility of your unknown solid in water.

  1. Add a small amount of your unknown solid to one of your test tubes. The amount should be roughly equivalent to the size of grain of rice.
  2. Add 10 drops of water to your test tube containing the unknown solid and agitate.

Refractive Index

Determine the refractive index of your unknown liquid. Correct use of the refractometer will be demonstrated by your laboratory instructor.

  1. Open the two part prism assembly.
  2. Place one drop of your unknown liquid on the prism. Be sure not to touch the prism to avoid scratching it.
  3. Close the two part prism assembly.
  4. Turn on the refractometer.
  5. Look through the eyepiece and adjust the coarse adjusting wheel until the cross hairs are at the junction of the light and dark field.
  6. Use the drum to sharpen the junction of the light and dark fields if necessary.
  7. Push down the on and off switch on the back left side of the instrument.
  8. Read the scale to four decimal places while looking through the eye piece.
  9. Open the two part prism assembly and clean with a Kim wipe and ethanol.

With the data you have collected for the density, boiling point and refractive index determine the identity of your liquid unknown.

Data Name____________________

_Solid Unknown #_____________________

Solubility

Water observations:

Ethanol observations:

Acetone observations:

Benzene observations:

Melting Point

Temperature where solid begins to melt: ____________________

Temperature where solid is completed melted: ____________________

Identity of unknown solid: ____________________

_Liquid Unknown #_____________________

Density

Mass of 1 mL of unknown liquid: ____________________

Density of unknown liquid: ____________________ (Show calculation)

Boiling Point

Temperature of boiling point: ____________________

Refractive Index: ____________________

Identity of unknown liquid: ____________________