Experiment#1: Boiling Point
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Enumerate the 4 Factors Affecting BP
• Atmospheric Pressure • IMFA • Molecular Structures • Impurities (added during post-lab discussion)
IONIC vs. COVALENT In comparing Ionic and Covalent compounds, which ones would have a lower BP, and which ones would have a higher BP?
Ionic - HIGH BP Covalent - LOW BP
ATMOSPHERIC PRESSURE [ATM] Above sea level, ATM ____ and BP ____.
ABOVE SEA LEVEL: ATM decreases, BP decreases.
ATMOSPHERIC PRESSURE [ATM] Below sea level, ATM ____ and BP ____.
BELOW SEA LEVEL: ATM increases, BP increases.
ATMOSPHERIC PRESSURE [ATM] Being that the BP of water is 100 °C at sea level, what then would be the (hypothetical) BP of water should you boil it at the top of Mount Everest? A) 300 °C B) 120 °C C) 68 °C D) 250 °C
C) 68 °C, because ATM decreases above sea level, therefore BP also decreases. Mount Everest is at a high altitude, well above sea level.
ATMOSPHERIC PRESSURE [ATM] Being that the BP of dodecane is 213 °C at sea level, what then would be the (hypothetical) BP of dodecane should you boil it at the bottom of the Mariana Trench? A) 200 °C B) 374 °C C) 118 °C D) 95 °C
B) 374 °C, because ATM increases below sea level, therefore BP also increases. The bottom of the Mariana Trench is well below sea level.
INTERMOLECULAR FORCES OF ATTRACTION [IMFA] If a compound has strong IMFA, its BP therefore is ____.
HIGH | The stronger the IMFA, the higher the BP
INTERMOLECULAR FORCES OF ATTRACTION [IMFA] If a compound has weak IMFA, its BP therefore is ____.
LOW | The weaker the IMFA, the lower the BP
TRUE or FALSE | EFFECT OF SURFACE AREA Molecules with larger surface area have stronger IMFA therefore higher BP.
TRUE
EFFECT OF BRANCHING If a molecule has branches (meaning: chains of other molecules attached to the parent molecule), it therefore has a ______ surface area, meaning a ______ BP.
DECREASED surface area = DECREASED BP
POLAR vs NONPOLAR In comparing Polar and Non-Polar molecules, which ones would have a higher BP?
Polar - HIGHER | Because they have stronger IMFA compared to Non-Polar molecules. A molecule having stronger Intermolecular Forces of Attraction means it requires a higher amount of energy for said forces to be broken down.
TRUE or FALSE | EFFECT OF POLARIZABILITY An increase in polarizability means a decrease in IMFA and therefore a decrease in BP.
FALSE, increased polarizability = increased IMFA = increased BP
INTERMOLECULAR FORCES OF ATTRACTION [IMFA] CH₃CH₂OH (Ethanol) vs CH4 (Methane) Ethanol is a polar molecule. Methane is a non-polar molecule with the existence of only London Dispersion Forces in its IMFA. Identify the FF: A) What IMFA does Ethanol contain? B) Now knowing the IMFAs of both compounds, which of the two, therefore, has the lower BP?
A) Ethanol contains Hydrogen Bonding forces because its chemical formula contains an H bonded to an O. B) Methane. Because Ethanol is both polar and contains the strongest IMFA as compared to Methane, which contains only the weakest IMFA (London Dispersion Forces)
CHANGE OF STATE: The transition from a solid to a liquid to a gas, and the reversal, represent ______ ___ - meaning there is only a change in the form or state of the substance.
Physical Change
CHANGE OF STATE: The following are examples of changes of states that require energy. What is this term called? • Melting [Solid to Liquid] • Vaporization [Liquid to Gas] • Sublimation [Solid to Gas]
Endothermic
CHANGE OF STATE: The following are examples of changes of states that release energy. What is this term called? • Freezing [Liquid to Solid] • Condensation [Gas to Liquid] • Deposition [Gas to Solid]
Exothermic
The temperature at which the vapor pressure of a liquid equals the external/atmospheric pressure.
Boiling Point
Occurs when bubbles of the liquid’s vapor form from the bottom (where it is hottest) of the liquid and rise to the surface.
Boiling
Characterized by change of phase from liquid to gas. (Vaporization, meaning there is a requirement of energy)
Boiling Point
BOILING POINT [BP] At what atmospheric pressure [atm] would a normal BP be?
1 atm (or 760 torr/760 mm Hg) Definition of Terms: ATM - Atmospheric Pressure; 1 atm is at sea level. mm Hg - milimeters (mm) mercury (Hg)
BOILING POINT [BP] Enumerate the 2 purposes of BP
• Identifying/Identification of Substances • To check the purity of liquid organic compounds
BOILING POINT [BP] These have a fixed or sharp BP.
Pure Substances
BOILING POINT [BP] These boil over a range of temperatures.
Mixtures
PROCESS OF OBTAINING THE BOILING POINT [BP] The presence of a continous stream of bubbles is due to the fact that the ____ pressure of the liquid sample inside the capillary tube is _____ than that of the _______ pressure outside of the tube.
The vapor pressure inside the capillary tube is greater than that of the atmospheric pressure outside of the tube.