CHM 1025C/CHM 1032C Lab

Experiment 5:  Physical and Chemical Properties

 

Objectives:

q             To determine the boiling points of methanol and an unknown liquid.

q             To determine whether a solid substance is soluble or insoluble in water.

q             To determine whether a liquid is miscible or immiscible with water.

q             To determine whether a substance is undergoing a physical or chemical change.

q             To observe sublimation of iodine

 

Discussion

 

One of the ways we classify matter is by its physical or chemical properties.  Matter can be classified as being homogeneous or heterogeneous.  Homogeneous matter has consistent physical and chemical properties throughout, regardless of the size of the sample being considered.  Examples of homogeneous matter include pure substances: elements and compounds, plus homogeneous mixture: solutions.

 

Heterogeneous matter is not consistent in terms of properties.  Sugar and salt mixed together may appear to be homogenous, but actually they form a heterogeneous mixture.  Their individual physical and chemical properties are quite different.  A heterogeneous mixture can be physically separated into two or more samples of homogenous matter.  Figure 5.1 illustrates the classification of matter, a modification of the Matter Chart in the Corwin text (Chapter 4).

 

 

Figure 5.1: Corwin’s Matter Chart modified with additional details

Table Sugar (Succrose) is an example of a homogeneous pure substance.  Upon heating, sugar decomposes into the element carbon and the compound water.  Furthermore, electricity decomposes water into the elements, hydrogen and oxygen.  Hydrogen and oxygen are both colorless gases under normal conditions, but they differ in their other physical and chemical properties.  Different elements may be identical in some properties but no two elements are identical in all properties.

 

Physical properties refer to those characteristics of a substance that can be measured or observed without the substance undergoing a change in composition.  The number of physical properties is quite extensive.

 

 A partial list of those that are usually considered important includes physical state (solid, liquid, gas), color, density, crystalline form, melting point, boiling point, electrical conductivity, heat conductivity, solubility, miscibility, malleability, ductility, hardness and a few others.

 

Chemical properties of matter can only be observed when a substance undergoes a change in composition.  That is a chemical reaction must take place.  Gasoline burning, copper metal turning green, and baking soda fizzing in water are all examples of a chemical change.  For every chemical change there is a change in energy.  If heat energy is released, the substance feels hot.  If heat is absorbed, it feels cool.

 

A chemical change is observed when:

1.         a gas is produced by mixing two chemicals (it doesn’t always have to bubble).

2.         an insoluble substance is formed (called a precipitate) or

3.         a permanent color change is noted.

 

In this experiment, we will record chemical changes if a permanent color change is noted, a gas is released, or an insoluble substance is formed after mixing two solutions.

 

Equipment and Chemicals

 

wire gauze

400 mL beaker                          

250 mL beaker

110º C thermometer

split cork or rubber stopper for thermometer

boiling chips

16 x 150 mm test tubes (6) and test tube rack

crucible tongs

evaporating dish

test tube brush

test tube holder

wash bottle with distilled water

ring stand and two rings

utility clamp to hold thermometer

methyl alcohol CH3OH

boiling point unknowns

iodine, solid crystals I2

sucrose, solid crystals C12H22O11

amyl alcohol, C5H11OH

copper wire, heavy gauge Cu

ammonium carbonate, solid (NH4)2CO3

sodium bicarbonate, solid NaHCO3

sodium carbonate solution, 0.5 M Na2CO3

dilute hydrochloric acid, 6 M HCl

sodium nitrate solution, 0.1 M NaNO3

lead (II) nitrate solution, 0.1 M Pb(NO3)2

potassium iodide solution, 0.1 M KI

 

 

 

 

 

 

 

Procedures

 

A.     Study of Physical properties

1.        Boiling point -

a.         Place a 400 mL beaker on a wire gauze and support it on a ring stand with a safety ring. Use a second ring as a safety ring  to protect the beaker from slipping off the ring stand Add 300 mL of water to the beaker, bring to a boil, and then shut off the burner.  Put about 2 mL of methyl alcohol into a test tube (1/10 full).  Add a boiling chip and place the test tube in the beaker of water.  Suspend a thermometer about 1 cm above the liquid. 

Figure 5.2

Allow the alcohol to boil in the water bath for a couple of minutes.  Record the temperature (± 0.5 ºC) after condensed vapor begins dripping from the tip of the thermometer (Figure 5.2)

 

Caution: Methyl alcohol is flammable and the vapors must not come near an open flame.

 

b. Record the number of an unknown liquid and determine the boiling point of the liquid

(± 0.5 ºC)  as above.

 

 

2.        Solubility -

            Add 5 mL of distilled water into two test tubes (1/4 full).  Place a small crystal of iodine in one and a crystal of sucrose (table sugar) in the other and shake the tubes for a couple of minutes.  State whether each substance is soluble or insoluble in water.

 

3.        Miscibility -

            Add 5 mL of distilled water into two test tubes.  Add a few drops of methyl

           alcohol to one test tube and amyl alcohol to the other.  Shake the test tubes

           briefly to mix the contents.  State whether each pair of liquids is miscible or

           immiscible.

 

       miscible: A term that refers to liquids that dissolve completely in one another.

 

       immiscible: A term that refers to liquids that do not dissolve in one another and separate into layers

 

 

 

B.     Study of Chemical Properties

 

1.                  Heating Elements

 

a.         Inspect a piece of copper wire.  Hold the wire with the crucible tongs and heat the wire until it glows red.  Allow the wire to cool and inspect once again.  State whether the change is physical or chemical.

 

Figure 5.3

b. Place a few small crystals of iodine in a dry 250 mL beaker.  Cover the beaker with an evaporating dish and place ice in the dish. (Figure 5.3). Support the beaker on a ring stand and heat the iodine slowly until all the vapor collects on the bottom of the evaporating dish.  State whether change is physical or chemical.

 

Caution:  When heating a test tube, the open end should be pointed in a safe direction.

              c. Cleaning the Evaporating Dish:

                   i. Scrape a few crystals off the evaporating dish into a test tube. Test the

                       crystals for water solubility.

 

              ii. Next use the Ethyl Alcohol (Ethanol) squeeze bottle and rinse the bottom

                 of the evaporating dish so that the drops of ethanol drip into the 600 mL

                 beaker on the front desk. Observe the color change as the purple iodine

                 crystals dissolve in the alcohol to make an iodine solution with Ethanol as

                 the solvent. (Solutions that use Ethyl Alcohol as the solvent are

                called Extracts in food chemistry and tinctures in medicine.)

 

2.                Heating Compounds

 

            Put a pea-sized portion of ammonium carbonate into one test tube and

          sodium bicarbonate into another.  Use a test tube holder and heat each test

          tube gently and note any odor.  State whether change is physical or chemical.

 

         3.       Solution Reactions

 

            a.         Put 2 mL of sodium carbonate into a test tube (1/10 full) and 2 mL of sodium sulfate into a separate test tube.  Add several drops of dilute hydrochloric acid to each test tube and record any changes.  Classify the change a physical or chemical.

 

                        Note:  No reaction is an example of physical change because the physical

                                 properties of mass and volume have increased.

 

            b.         Put 2 mL of sodium nitrate into a test tube and 2 mL lead (II) nitrate into a separate test tube.  Add a few drops of potassium iodide to each test tube and note any changes.  Classify the change as physical or chemical.