Exploring Boilng Points Lab

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Exploring Boiling Points

Introduction:
Every substance has a unique set of properties that allow us to differentiate between them. These properties are classified as physical properties and chemical properties. Physical properties are those that can be determined or measured without changing the composition or identity of the substance. These properties include color, odor, taste, density, melting point, boiling point, conductivity, and hardness. Chemical properties tell us how the substance interacts with other substances and may include reaction with oxygen (oxidation), chlorine, metals, etc. Determination of chemical properties results in the change of the identity of the substance. Some properties, such as solubility, melting point, boiling point, and density are independent of the amount of substance being examined. These properties are known as intensive properties and are used to identify a substance. Extensive properties, such as mass and volume depend on the amount of substance present and are not useful in the identification of a substance. The physical properties of a pure substance can be used to identify the substance and distinguish it from other pure substances. Boiling temperature is one such physical property. Boiling is characterized by the formation of vapor bubbles within the liquid phase as a substance changes from a liquid to a gas. But in order for this to occur, we must apply heat to the liquid at a constant pressure and observe the temperature increase. The point at which the temperature no longer increases even when heat is being added, and when bubbles begin to form and the liquid is being converted to a vapor, is known as the boiling point of the liquid. This can be formally described as the temperature at which a substance (solid or liquid) boils when the pressure is 760mmHg or 1 atm. At the boiling point, the temperature of the liquid is the same as the escaping vapor (or gas). Although the boiling point does vary slightly with the prevailing atmospheric pressure, we will use the normal boiling points at one atmosphere Different substances have different boiling points, and this is due to different trends. In this experiment, we would be observing the boiling points of a group of similar compounds by looking at the straight-chain alkane hydrocarbons. Different trends such as Molecular weight, symmetry, density, solubility and Intermolecular forces can be observed. We will begin by analyzing group of similar compounds – hydrocarbons to see how their boiling point vary with molecular weight. Normal Boiling Points of the Straight-Chain Alkane Hydrocarbons Compound

NameChemical
FormulaMolar
Mass
(g/mol)Normal
Boiling
Point (K)
MethaneCH416.0111
EthaneCH3-CH330.1185
PropaneCH3-CH2-CH344.1231
ButaneCH3-CH2-CH2-CH358.1273
PentaneCH3-CH2-CH2-CH2-CH372.2309
HexaneCH3-CH2-CH2-CH2-CH2-CH386.2342
HeptaneCH3-CH2-CH2-CH2-CH2-CH2-CH3100.2372
OctaneCH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3114.2399
NonaneCH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3128.0424

Objective:
To observe the boiling points of a group of similar compounds by looking at the straight chain alkane hydrocarbons. Firstly, we will create a graph of the data for the straight chain alkane hydrocarbons, then, look up their structural formulas, molar masses and boiling points of five other compounds. Methods:

Instruments:
Microsoft excel to plot graph.
Desk 137E
CompoundMolar Mass (g/mol)Normal Boiling Point (K)
A (11) 2,2,3-trimethylbutane100.2019354.1 ± 0.2
B (18) 2-pentanone86.1323375. ± 1
C (21) 3-methyloctane128.2551417. ± 1
D (30) methyl alcohol32.0419337.8 ± 0.3
E (32) propene42.0797225.6 ± 0.6

Procedure
Excel is used to make a plot of the normal boiling points of the straight chain alkane hydrocarbons using the data in the introduction. •Any point on the graph is right clicked, trend line added and polynomial option with an order of 2 is selected. •Another set...
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