Solubility and Electrical Conductivity of molecular and ionic solids | Sugar| Sodium Chloride| Iodine|

Solubility and Electrical Conductivity of molecular and ionic solids | Sugar| Sodium Chloride| Iodine|

Aim / Objective:

To investigate the solubility and electrical conductivity of molecular and ionic solids.

Introduction: 

Ionic solids are formed by ionic bonding where the particles in the solids are ions. These solids are crystals because of their structures. The regular structure of a crystal tells you that the ions are arranged in an orderly manner. This orderly arrangement is a crystal lattice.

Most substances that contain covalent bonds are also described as simple molecular substances, because they consist of separate molecules. Sugar is a molecular crystal which has a low melting and boiling point.

Sodium Chloride is an ionic compound which has a high melting and boiling point due to strong forces which exist between the ions.

Iodine, like sugar is described to be a molecular crystal for it consists of separate molecules.

Materials/ Apparatus:

Iodine and Sugar solid (molecular solids), sodium chloride (ionic solid), distilled water (polar solvent), tetrachloromethane (non-polar solvent), beaker, electrolytic cell, test tubes, measuring cylinder.

Method / Procedure:

  1. Label three test-tubes A, B and C. In test tube A put one crystal of iodine solid.
  2. In test-tube B, put a spatula full of sugar and finally in test-tube C put a spatula full of sodium chloride.
  3. Add 5cm3 of distilled water to the three test tubes. Record your observations.
  4. Repeat steps 1 and 2, then add 5cm3 of tetrachloromethane and record your observations.
  5. Tabulate results.
  6. Label three (3) beakers A, B and C. In beaker A, mix one crystal of iodine and 25cm3 of tetrachloromethane.
  7. In beaker B, mix three spatulas full of sugar and 25cm3 of water and in beaker C, mix three spatulas full of sodium chloride and 25cm3 of water.
  8. Place electrodes into the solutions and close the switch. Watch the ammeter for readings and record the registered reading to determine if the solution conducted an electric current.
  9. Tabulate results.

Suggested Results: 

Table showing the electrical conductivity of iodine, sugar and sodium chloride

Table showing the electrical conductivity of iodine, sugar and sodium chloride

Table showing the solubility of sugar, iodine and sodium chloride in water and solvent

Table showing the solubility of sugar, iodine and sodium chloride in water and solvent

Discussion/Answers:

1. State the reason(s) why sugar did not conduct electricity when dissolved in water

>>>This is due to the absence of ions, for when ions are set free they move to an oppositely charge electrode when a voltage is applied.

2. State the reason for the differences in solubility of sugar in water and tetrachloromethane

>>>The reason why sugar dissolves in water and not in tetrachloromethane is because sugar has polar hydroxyl groups and polar substances dissolve in polar solvent (water), whereas they do not dissolve in nonpolar organic solvent (tetrachloromethane).

3. Explain why sodium chloride was the only substance that conducts electricity

>>>The sodium chloride solutions conducts electricity because the ions are set free upon melting and these ions will furthermore move to an oppositely charge electrode when a voltage is applied.

4. State the reason for the differences in solubility of NaCl in water and tetrachloromethane

>>>The reason why sodium chloride dissolves in water and not in tetrachloromethane is because NaCl has polar hydroxyl groups and polar substances dissolve in polar solvent (water), whereas they do not dissolve in nonpolar organic solvent (tetrachloromethane).

5. Why did iodine not conduct electricity?

>>> Iodine did not conduct electricity when molten or dissolved due to the absence of ions from its structure.

6.  State the reason for the differences in solubility of iodine in water and tetrachloromethane

>>>Iodine consists of molecules and dissolves in tetrachloromethane and is insoluble in water. This is because tetrachloromethane is a non-polar organic solvent and water is a polar solvent, and with iodine being a non-polar molecular substance it will readily dissolve in solvents that are non-polar. This means essentially that the atoms of the element are identical and has the same attraction to the tetrachloromethane.

Source of Error/ Limitations/ Assumptions: 

–          Incorrect reading from the ammeter

–          Contamination of solids resulting in incorrect voltage readings

–          Parallax error

–          Incorrect measurement of solutions

–          Not dissolving solids completely

Remember to always consult your textbook for any other useful information that would really impress your teacher.

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