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Experiment 6- Bonding and
Properties Title: Bonding and Properties
Purpose: To study the infrared spectra and physical properties of molecules to determine
what kinds of intra-molecular bonds are present within molecules and what kinds of inter-
molecular bonds are present between the molecules.
Procedure:
Water Solubility •Potassium Chloride
•Adding Potassium chloride (ionic substance) and it forms strong bonds with water
molecules
•White solid disappears as water is shaken to allow it to interact
•Potassium Chloride is soluble in water which indicates that it is either ionic polar or
hydrogen bonding compound
•Non polar molecules will NOT dissolve in water
•We can determine polar or non polar based on the boiling point
•Pentane
•Add pentane to water; you dont see a solid bc pentane is liquid; BUT there is a layer of liquid on top of the water
•Test tube is shake and the layer remains so
•Pentane is not water soluble so it must be nonpolar
•N-Propal Chloride
•Liquid layer on top of water
•Shaken and the layer is still ther
•Did NOT disolve in water so that indicates it is non polar or not very purple
•Ethyl Alcohol
•It sits at top of solution
•It is shaken and it dissolves; no layer on top or bottom
•N-Butyl Alcohol
•Mixed with water and there is a layer floating on top
•Shaken and it gets cloudy
•Somewhat soluble but not totally= partially soluable
•T- butyl alchol
•Small layer on top but it disappears very quickly and totally dissolves
•IS soluble in water
•Acetic Acid
•No layer bc it is already dissolved
•Very soluble in water so its polar, ionic, or hydrogen bonding
Boiling Point Study : Molecular bonding can often be determined from studying the physical properties of the molecules, especially the boiling points of liquid materials. We will measure the https://www.coursehero.com/file/76705416/chem-lab-6-donedocx/This study source was downloaded by 100000824189183 from CourseHero.com on 08-25-2021 02:39:58 GMT -05:00boiling points of some* of the materials listed in the chart on the next slide and compare all
boiling points to determine facts about intermolecular bonds present between molecules
Effect of Intermolecular Forces
The boiling points of substances are greatly affected by the inter-molecular forces between the molecule which are holding them together in aggregates causing them to exist in the liquid state.
The stronger these forces, the more energy will be required to separate the aggregates into individual gaseous molecules (the higher will be the boiling points of the molecules with greater
intra-molecular forces)
The relative strength of inter-molecular forces is:
Ionic>Hydrogen-bondng> dipole-dipole>Van der Waals
Effect of Molecular Weight
Maong substances with relatively similar intermolecular forces, the higher the molecular weight the greater the mass of the molecules and the greater their surface area. Greater surface area causes stronger attractions between the heavier molecules requiring more energy to separate the molecules into individual gaseous molecules, so the higher the molecular weight, molecules will have the higher boiling points Effect of Branching (Symmetry)
Among substances with relatively similar intermolecular forces and molecular weights, a greater
degree of branching causes those molecules to have greater symmetry. Greater symmetry results
in a lower surface area requiring less energy to separate the molecules into individual gaseous molecules, so the molecules with greater degree of branching will have lower boiling points. An ionic substance (like potassium chloride, KCl, in the previous list) since it has the strongest
inter-molecular forces, should have the highest boiling point.
A completely non-polar (like n-pentane, CH3CH2CH2CH2CH3, in the previous list) since it has the weakest inter-molecular forces, should have the lowest boiling point.
A polar (but non-hydrogen bonding) substance (like n-Propyl chloride, CH3CH2CH2Ck, in the
previous list) since it has the second weakest inter-molecular forces, should have the lowest boiling point.
Hydrogen bonding molecules (like acetic acid, ethyel alcohol, n-butyl alcohol and t-butyl alcohol, in the previous list) since they have the second strongest inter-molecular forces, should have the second highest set of boiling points.
Now that the boiling points have been determined by the distillation or from data tables, lets look
at the data ans see if it matches the predictions.
Infrared Spectrometry A Infrared spectrometer is an instrument that passes a beam of infrared light through a sample causing the bonds of the sample molecules to bend or stretch as IR energy of certain wavelengths are absorbed.
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