Experiment 1 Identification of a Compound: Physical Properties I NTRODUCTION Gold is yellow, roses are often red, salt is white and crystalline, lead is "heavy," and water is a colorless, clear liquid that freezes at 0°C and boils at 100°C. These are physical properties of substances that are often used for their identification. The more common physical properties include color, odor, density, solubility, melting point, boiling point, and state of the substance (solid, liquid, or gas). Physical properties can be observed or measured without any knowledge of the chemical reactivity of the substance. Additional tests, tests that reveal more information about its chemical or physical properties, may be necessary to confirm the purity of the substance. The purpose of this experiment is to identify a substance based on its solubility, density, melting point, and/or boiling point, all of which are physical properties and intensive properties (a property independent of sample size) of a substance. In Experiment 2, the chemical properties of a substance are used for its identification. Solubility Solubility: the maximum mass (usually in grams) that dissolves in a fixed mass (usually 100 g) of solvent at a given temperature. A substance has different solubilities in different solvents, reflecting the differences in the molecular compositions and molecular structures of the substance and the solvent. For instance, some substances, such as table salt, are soluble in water but insoluble in gasoline. In this experiment, we examine the solubility of a substance in three different solvents: water, ethanol, C2H5OH, and acetone, (CH3)2CO. If further solubility tests are required then cyclohexane, C6HI2, is used as a solvent. Qualitatively each substance is recorded as being soluble (complete dissolution) or insoluble. Density Density: the ratio of the measured mass of the substance to its measured volume. A substance with a large density has a large mass occupying a small volume. We commonly say that lead is "heavy." What we really mean is that lead has a large density; the volume of a lead object need not be large for it to have a large mass. Melting Point Melting point: the specific temperature that a solid changes completely into a liquid . At the melting point the solid and liquid phases coexist; any lowering of the temperature results in the formation of only solid, and any raising of the temperature results in the existence of only the liquid phase. Boiling Point Boiling point: the temperature at which the vapor pressure (the pressure exerted by a vapor when it is in dynamic equilibrium with its liquid) of a liquid equals atmospheric pressure Atmospheric pressure: the force (or weigh) that a column of air exerts over an area of the earth's surface Intermolecular forces: interactive attractions and repulsions between molecules When a liquid is heated, there is a temperature at which bubbles form spontaneously and continue to form until all of the liquid has been converted to vapor. This constant temperature is called the boiling point of the liquid, a temperature at which the liquid and vapor phases coexist. The boiling point of a liquid depends on the prevailing atmospheric pressure. The boiling point values listed in Table 1.1 are measured at normal atmospheric pressure (defined as 1 atmosphere of pressure).

The melting and boiling points of a substance are characteristic of the magnitude of the forces acting between molecules, called intermolecular forces. The greater the magnitude of the intermolecular forces (i.e., the stronger the attraction between molecules), the higher the melting and boiling points of the substance. As the magnitude of the intermolecular forces is different for each substance, each has a characteristic melting point and boiling point. Table 1.1 Physical Properties of Some Common Laboratory Chemicals Compound Acetone Acetamide Acetanilide Anthracene Benzamide Benzoic acid Benzoin 2-Butanone Cyclohexane Cyclohexene Ethanol Ethyl acetate Heptane n-Hexane 1-Hexane Methanol Naphthalene 1-Propanol 2-Propanol Water

Density Melting 3 o (g/cm ) Point ( C) 0.79 -95 1.00 82.3 1.22 114 1.28 216 1.08 132 1.07 122 1.31 137 0.81 -86 0.79 6.5 0.81 -104 0.79 -117 0.90 -84 0.68 -91 0.66 -95 0.67 -140 0.79 -94 0.96 80.5 0.80 -127 0.79 -90 1.00 0

Boiling Water o Point ( C) 56 s (b) 221 s 304 290 249 344 80 81 83 79 77 98 69 63 65 218 97 82 100.0

s

s

s s

s s s -

Ethanol s s s s s s s s s s s s s s s s s s

Acetone

Cyclohexane

-

s

s s

s s s s

s s s s s s s s

s s s s s

s s s s s s s s s s

PROCEDURE Obtain an unknown listed in Table 1.1 from your instructor. A. Solubility 1. Solubility in Water. To a small test tube add a pinch (a sample about the size of a grain of rice) of your solid or 3 drops of your liquid unknown to 1 mL of water. Agitate the contents. Does your unknown dissolve? Record your observations. Describe the solubility of your unknown as soluble(s) or insoluble(i) in each solvent. 2. Solubility in Ethanol and Acetone. Repeat the test with ethanol and acetone as solvents. (Caution: Avoid breathing vapors; acetone is flammable--keep away from flames 3. Solubility in Cyclohexane. If the solubility of the unknown is still uncertain, repeat the solubility tests using cyclohexane as a solvent. B. Density of Liquid Unknown Complete two trials to determine the density of your liquid unknown. 1. Determine Mass and Volume. Determine the mass (∓0.001 g) of your smallest laboratory beaker. Pipet 2 mL of the liquid sample into the dry, clean beaker. Measure the combined mass of the liquid sample and beaker. (Note: Use a rubber pipet bulb in drawing the liquid into the pipet.) Calculate the density of the liquid.

C. Melting Point of a Solid Unknown 1. Prepare the Sample. Fill a capillary melting point tube to a depth of 0.5 cm with the solid unknown. Compact the solid to the bottom of the tube by dropping it several times onto the lab bench through a glass tube at least 25 cm in length or by vibrating the sample with a triangular file. Attach the tube to a 360°C thermometer with a rubber band (or band of rubber tubing). Place the sample alongside the thermometer bulb. 2. Set up the Melting Point Apparatus. Obtain a 360°C thermometer. Assemble the melting point apparatus below. Note that cooking oil is the liquid that is heated in the 50mL beaker.

: 3. Determine the Melting Point. Slowly heat the oil bath (at a rate of about 5°C per minute) until the solid melts. (Caution: The oil bath may be at a temperature greater than 100°C---do not touch!) Cool the oil bath until the sample solidifies; very slowly (at a rate of about 1°C per minute) heat the bath until the solid again melts. Cycle the cooling and heating of the oil bath until the melting point of the solid has been accurately determined. Complete two measurements for the melting point of your unknown. *Disposal: Dispose of the capillary tube into the broken glass container and the pour the cooled oil back into the oil containers. D. Boiling Point of Liquid Unknown 1. Assemble the Boiling Point Apparatus. Place 10 drops (0.5 mL) of the liquid unknown into a "'small" (75-mm) test tube and a boiling stone. (Caution: The liquid may be flammable-extinguish all flames!) A piece of fire resistant wire gauze with a small hole is placed on a ring. Lower a thermometer (capable of measuring to at least 150 C) until the bulb is 0.5-1.0 cm above the surface of the liquid. Center the thermometer by adjusting the thermometer clamp so that the bulb does not contact the inner walls of the test tube. 2. Measure the Boiling Point Adjust your burner to a very low flame and manipulate it beneath the hole in the gauze until a gentle boiling of the liquid takes place. Gentle boiling is essential for the success of this determination. Violent boiling will result in a rapid loss of the

sample and possibly increase the danger of its becoming ignited by the burner flame. (Caution: If fire occurs, remove the burner and extinguish the flame by blowing across the opening of the test tube. Let it burn out if it doesn't blow out.) Record the boiling point of the liquid when the vapor condenses on the thermometer bulb and drips off in a series of steady drops and the temperature no longer rises. Complete two measurements for the boiling point of your unknown. 3. Extinguish the Bunsen flame before disassembling the apparatus. Allow plenty of time for the test tube to cool before disassembling and cleaning.• Disposal: Dispose of the leftover unknown substance in the "Waste Organics “container in the fume hood.

Name _____________________________ Identification of a Compound: Physical Properties Experiment1 : Prelab Assignment 1. What is the purpose of this lab?

2. From your general experiences, would you select water or gasoline to try dissolving the following? a. Table sugar (sucrose), used to satisfy your sweet tooth

b. Table salt (sodium chloride), thrown over your shoulder for good luck!

c. Motor oil that has dripped from your automobile onto the garage floor

d. Road tar on the side of your automobile

e. Fertilizer that has spilled from an overturned truck

f. Rubber from the tire marks left on your driveway

g. Blood from a "squished" mosquito

h. Adhesive from a pricing sticker that adheres to a glass vase

2. A student's liquid unknown boils at approximately 65°C and is soluble in water and ethanol. Its measured density is 0.80 g/ml. Which substance in Table 1.1 is the student's unknown?

3. What physical property, measurable in this experiment, distinguishes 1-propanol from 2-propanol? (Keep in mind the state of these compounds)

4. During the boiling point determination, when should the boiling point of a liquid be recorded?

5. Identify the essential steps for placing a solid sample in a capillary tube.

Name _______________________________ Identification of a Compound: Physical Properties Experiment1 : Prelab Assignment Data & Calculations Table: (Show work if applicable.) A. Solubility Unknown Number I. Solubility in water 2. Solubility in ethanol 3. Solubility in acetone 4. Solubility in cyclohexane, if necessary

B. Density of Liquid Unknown 1. Mass of beaker and liquid (g) 2. Mass of beaker (g) 3. Mass of liquid (g) 4. Volume of liquid (mL) 5. Density of liquid (g/mL) 6. Average density of liquid (g/mL)

C. Melting Point of Solid Unknown 1. Observed melting point (°C) 2. Average melting point (°C)

D. Boiling Point of Liquid Unknown 1. Observed boiling point (°C) 2. Average boiling point (°C) E. Name of Unknown . Please justify your answer.

Conclusion Questions: I. How does atmospheric pressure affect the boiling point of a liquid?

2. Suppose that in Part B, the liquid unknown remaining in the pipet is "blown out" after delivery. Will the reported density of the liquid be too high or too low? Explain.

3. Besides the physical properties used to identify a substance in this experiment, what other physical properties might be used to characteristically identify a substance?