EXPERIMENT NO : 3

TYPES OF BONDS

All matter is held together by force. The force between atoms within a molecule is a chemical or intramolecular force. The atoms of a compound are held together by chemical bonds formed by the interaction of electrons from each atom.

Types of Chemical Bonds

While the intramolecular forces keep the atoms in a molecule together and are the basis for the chemical properties, the intermolecular forces are those that keep the molecules themselves together and are virtually responsible for all the physical properties of a material. The intermolecular forces are weaker than the intramolecular forces. The forces that are responsible for physical properties of substances increase in strength according to the following:

London dispersion < dipole-dipole < H-bonding < ion-ion

Now, as these things increase in strength it becomes harder to remove the molecules from each other. Therefore, one would expect the melting and boiling points to be higher for those substances, which have strong intermolecular forces.

The dissolving process involves a consideration of type of forces betweensolute-solute moleculesandsolvent-solvent molecules. A solute will dissolve in a solvent if the solute-solvent forces of attraction are great enough to overcome the solute-solute and solvent-solvent forces of attraction. A solute will not dissolve if the solute-solvent forces of attraction are weaker than individual solute and solvent intermolecular attractions. Generally,

LIKES DISSOLVE LIKES.

This means that ionic or polar solutes dissolve in polar solvents.
Non-polar solutes dissolve in non-polar solvents.

Polar and ionic solutes DO NOT dissolve in non-polar solvents and vice versa.

Remember that when applying the solubility rule: "Likes Dissolve Likes", that there are no absolutes and there are exceptions with a small amount of solubility possible.

Solutions that contain electrolytes conduct an electric current, indicating the presence of mobile ions. A substance that dissociates completely in water (e.g. KCl or HCl) is said to be a strong electrolyte and will generally be a good electrical conductor whereas a substance that dissociates only to a small extent (e.g. CH3CO2H, which is only 1% to 5% dissociated in water) is called a weak electrolyte, and conducts to a much more limited extent. A substance that does not dissociate at all when dissolved in water (e.g. C2H5OH) is called a nonelectrolyte.

In this experiment you will

  • compare melting points of different chemicals to arrange the chemicals in order of decreasing strength of intermolecular forces.
  • look at the solubility of different chemicals in two solvents: water and vegetable oil and identify the chemicals as polar or nonpolar.
  • build a conductivity tester to determine whether any of the resulting solutions contain electrolytes.

ENVIRONMENTAL CARE:Use very small quantities of chemicals to minimise both cost and damage to the environment.

SAFETY: Exposure to iodine can irritate the nose and throat. Iodine can affect you when inhaled and may be absorbed through the skin. While heating iodine, use a very smallamount of it andclose the test tubewith a stopper and do NOT remove the stopper until the very end of the experiment.Iodine is not combustible, but strong OXIDIZER.

CCl4 is TOXIC, harmful by inhalation, in contact with skin, and ingestion. Always handle CCl4 inside a chemical fume hood. Do NOT breathe the vapor. Use only with adequate ventilation.

Make sure all the bottles of chemicals are well closed when not in use.All chemicals used in this experiment are severely corrosive to eyes, skin, and other tissue. Wear lab coat at all times. Avoid skin contact with chemicals and do notinhale them. Wash the chemicals immediately from skin and clothes. You must wear safety goggles at all times.In case of eye contact, immediately flush with large amounts of water for at least 15 minutes, lifting upper and lower lids. Remove contact lenses, if worn, while rinsing.

Remember that hot and cold glass have the same appearance.

ASSESSMENTCRITERIA:None.

PROCEDURE:

PART A: What Order do they Melt?

  1. Put about 1/4th of a spatula of Iodine into a pyrex test tube. Close the test tube with a stopper.
  2. Heat up the test tube directly in the middle layer of the flame and record the time needed to start first melting or change in the solid (Warning! Do NOT remove the stopper from the tube). If there is no change in the solid after 2 minutes, stop heating the solid and say “no melting” in the related section of the data table.
  3. Repeat the steps 1 and 2 by substituting Iodine with the following chemicals respectively:

Sucrose, NaCl, Oxalic acid, NiCl2, and Starch

PART B: Polar vs. Nonpolar Solvents

Figure 1.Two burettes filled up with water and vegetable oil.

  1. Fill two burettes up with water and vegetable oil as shown in Figure 1.
  2. Charge a glass rod using pieces of silk or fur. Make asmall stream to exit each burette and hold the charged rod next to the streams of the burettes.
  3. Write your observations down.

PART C: Solubility in Water and Vegetable Oil

  1. Put about 1/4th of a spatula of each of the following chemicals into separate beakers of 100 mL.

Iodine, Sucrose, NaCl, Oxalic acid, NiCl2, and Starch

  1. Add 40 mL of distilled water into each of the test tubes.
  2. Stir each mixture with a stir rod for about one minute. Record your observations as “soluble or insoluble” in the data table. Do NOT dispose the mixtures of chemicals in water since they are going to be used in part D.
  3. Repeat the steps 1-3 by substituting water with vegetable oil. The mixtures with oil will not be used in part C.

PART D: Electrical Conductivity

  1. Set up the apparatus given in Figure 2 below with the aqueous mixtures that were prepared in part C to test the conductivity of the mixtures. Use about 6V in the generator.
  2. Test the conductivity of each of the mixtures by dipping the ends of the two Cu electrodes into each mixture. Bring the Cu electrodes closer to each other in the mixture but do NOT make them touch each other in the mixture. In the data sheet, indicate the result as electrolyte or nonelectrolyte.

Figure 2. Experimental setup of the circuit to test the electrical conductivity of the mixture.

PART E: Solubility, “Like Dissolves Like” (Demonstration)

  1. Prepare the setup given in Figure 1 below.
  2. Add about half a spatula of I2crystals to the first funnel shown in Figure 3 below.
  3. Add about half a spatula of KMnO4crystals to the second funnel.
  4. Write your observations down about the solubility of the two chemicals.

Figure 3. The setup showing the chemicals used in part D.

REFERENCES:

  1. Intermolecular forces. Retrieved on 10.12.2013 from the web
  2. Intermolecular forces. Retrieved on 10.12.2013 from the web
  3. Intermolecular forces. Retrieved on 10.12.2013 from the web
  4. Solubility and Electrical Conductivity. Retrieved on 10.12.2013 from the web
  5. Working with I2. Retrieved on 10.12.2013 from the web
  6. Working with CCl4.Retrieved on 10.12.2013

Date ______Name ______IB 1

Partner’s name(s) ______

DATA:

PART A:What Order do they Melt?

  1. Observations:
  1. Prediction about the melting order:

Iodine / Sucrose / NaCl / Oxalic Acid / NiCl2 / Starch

Your reasoning about the prediction:

  1. Experimental results about the melting order

Iodine / Sucrose / NaCl / Oxalic Acid / NiCl2 / Starch
  1. Decreasing order according to the strength of intermolecular forces based on the experimental results

Iodine / Sucrose / NaCl / Oxalic Acid / NiCl2 / Starch

PARTB:Polar vs. Nonpolar Solvents

Observations:

Conclusion about the polarity of the solvents based on observations:

PART C: Solubility in Water and Vegetable Oil

  1. Prediction about the solubility in water:

(Label each as soluble or insoluble)

Iodine / Sucrose / NaCl / Oxalic Acid / NiCl2 / Starch

Your reasoning about the prediction:

  1. Experimental results about the solubility in water:

Iodine / Sucrose / NaCl / Oxalic Acid / NiCl2 / Starch
  1. Prediction about the solubility in oil:

(Label each as soluble or insoluble)

Iodine / Sucrose / NaCl / Oxalic Acid / NiCl2 / Starch

Your reasoning about the prediction:

  1. Experimental results about the solubility in oil:

Iodine / Sucrose / NaCl / Oxalic Acid / NiCl2 / Starch

PART D: Electrical Conductivity

Identify the substances as electrolyte or nonelectrolyte based on your observations.

Iodine / Sucrose / NaCl / Oxalic Acid / NiCl2 / Starch

PART E: Solubility, “Like Dissolves Like” (Demonstration)

  1. Observations:
  1. Reasoning behind different solubility of Iodine and KMnO4 in different solvents.