EXP 6: Micro-Determination of Boiling Point & Melting Point

Boiling Point

Temperature at which the vapor pressure is equivalent to the external/atmospheric pressure exerted at any point upon the liquid surface

vapor pressure; external/atmospheric pressure

Boiling point is the temperature at which ___ ___ is equivalent to the ___ ___ at any point upon the liquid surface

When boiling point varies with atmospheric pressure

When does the boiling point become not as a reliable criterion as melting point?

Showing the compounds’ physical constants is near the results already recorded in literature

How is the purity of organic compounds determined?

Density, Refractive Index, Molecular Weight, Melting Point, Boiling Point

What constants of compounds can be used to determine the compounds’ purity?

Melting Point & Boiling point

What constants are recorded for organic compounds to determine purity?

Melting Point

Temperature at which the solid and liquid forms of a compound exist in equilibrium with each other at atmospheric pressure

solid and liquid forms; equilibrium

Melting point is the temperature at which the ___ ___ ___ ____ of a compound exist in _____ with each other at atmospheric pressure

Temperature when melting of the substance begins & Temperature at which sample is entirely liquefied

What two temperatures are recorded during procedures with melting point?

temperature range

The term “melting point” really signifies the ____ ___ that is observed

Depressed below the true melting point

What is the melting point in organic compounds with impurities compared to the pure compound?

Greater than true melting point range

What is the melting point range in organic compounds with impurities compared to the pure compound?

Range between incipient and complete liquefication

Another way to describe melting point range?

Can be used to identify a compound by comparison to tables with known values AND gives an approximate indication of the compound’s relative purity

2 reasons why melting point in useful/important?

Compounds melting point is accurate compared to known values OR recrystallization (or other purification method) of the compound from two different solvents fails to increase the melting point temperature or decrease melting point range

2 occurrences when compound is considered pure

Ethyl Alcohol (CH3CH2OH)

What substance’s boiling point is being determined in Experiment 6?

2 cc

How much ethyl alcohol (CH3CH2OH) is used in boiling point determination?

2.5 cm

How far above the liquid’s surface must the thermometer bulb be during boiling point determination?

Ensure whole column of liquid is heated, preventing sudden cooling

Why should the bunsen burner be held in the hand during boiling point determination?

Vapor will condense into liquid, forming condensation ring at least 1 cm above thermometer bulb

What will occur at the cooler part of the test tube during boiling point determination?

Liquid boils, drops regularly fall from thermometer bulb, and temperature reading is constant

What are the three requirements when the observed boiling point will be recorded?

Capillary Tubes

What apparatus are the substances placed in during melting point determination?

Outer mantle of small flame

What is used to seal the end of the capillary tube?

1 for the benzoic acid (C6H5COOH) and 2 for the unknown substance

How many capillary tubes were used in Experiment 6?

Benzoic acid (C6H5COOH) from sublimation in past Experiment 4

What substance was used in the preliminary trial of melting point determination?

Open end of the capillary tube is pressed on small heap of sample on paper then flipped over then tapped lightly on table top

How should the sample be placed in the capillary tube in preparation for melting point determination?

3-5 mm

What is the sufficient depth of the substance in the capillary tube?

Rubber Band

What is used to fasten the thermometer to the capillary tube?

Mercury Bulb

What part of the thermometer should the sample in the capillary tube be close to?

100 mL

What is the size of the beaker the capillary tube and thermometer are dipped in during melting point determination?

60 cc coconut oil (C12H7Cl3O2)

What is the measurement and the substance is placed in the 100 mL beaker and acts as the heating bath?

1 cm

How far from the bottom of the beaker should the mercury bulb be dipped during melting point determination?

Stirred with a stirring rod to ensure heat is distributed evenly to substance in tube

What MUST be done to the oil bath during heating?

1-2 degrees Celsius/minute

The rate of heating should be enough to cause an increase in temperature by ___

122.3 degrees Celsius

What is the standard average melting point of benzoic acid (C6H5COOH)?

121.5-123.5 degrees Celsius

What is the standard melting range of benzoic acid (C6H5COOH)?