Melting Point Ranges-BLANK

Attractive forces between the permanent dipoles of two polar molecules.

The temperature at which a solid melts or the energy needed to break apart solid molecules.

Impurities lower the melting point.

Ionic bonds typically lead to higher melting points compared to covalent bonds.

An extra strong type of dipole-dipole interaction that occurs when a hydrogen atom bonded to O, N, or F is electrostatically attracted to a lone pair of electrons on an O, N, or F atom in another molecule.

No, it is not the only way to identify a compound.

They 'hog' electron density, creating partially negative and partially positive areas of the molecule.

In 1958.

Because hydrogen bonding makes ice less dense than water.

Run a melting point and compare it to literature values.

Larger molecules generally have higher melting points due to increased van der Waals forces.

Pure substances have a sharp melting point, while impurities lower and broaden the melting point range.

Sigma-Aldrich catalogue, ChemSpider, or Wikipedia.

To establish an unknown solid’s identity, determine the purity of a solid, and report the physical properties of a new compound.

Because co-crystals are designed to improve solubility, tableting, and thermal stability.

82-83 °C

Oxygen (O), Nitrogen (N), or Fluorine (F).

178 – 179 °C

Solubility, tableting, and thermal stability.

Larger molecules tend to have higher melting points.

165 – 172 °C

Salts interfere with water’s crystal lattice, requiring less heat to melt the ice.

Supramolecular assembly, such as crystal packing with intramolecular interactions like pi-stacking and van der Waals interactions, can lead to higher melting points.

The presence of impurities.

A co-crystal formed in a 1:1 ratio of two compounds.

Increased pressure can raise the melting point of a substance.

The more a molecule can create partially negative and positive areas due to changes in electron density, the more 'polarizable' it is.

To identify and characterize compounds, and to assess their purity.

To determine the identity of an unknown compound by mixing it with a known compound and observing the melting point.

172 - 175.5 °C

Hydrogen bonding increases the melting point due to stronger intermolecular forces.

Organic compounds melt over a range of temperatures.

Only useful with solids.

175-178 °C.

Purity of the compound, presence of impurities, and intermolecular forces.

It means the unknown compound is likely the same as the known compound.

The melting point of a co-crystal will always be lower than at least one of the pure compounds.

Because many compounds have similar melting points and experimental values can vary.

Momentary changes in electron density in a molecule.

Pure compounds have sharp melting point ranges of only ~1 - 2 degrees, while impure compounds have a much larger and lower (depressed) range.

New spectroscopy techniques have made melting points a bit obsolete.

51-60 °C.

113 - 115 °C

Establishing an unknown solid’s identity, determining purity, and reporting physical properties of new compounds.

34-36 °C.

Because you might have a different compound with similar melting points.

It indicates that the unknown compound is not the same as the known compound.

170 - 172 °C

The temperature range that starts when you see the first drop of liquid and ends when no solids remain.

m-Phenylenediamine, with an experimental melting point range of 51-60 °C.

Higher pressures change the ease of expansion/contraction upon melting, affecting the melting point.

Impurities disrupt the crystal lattice, causing a broader and lower melting point range.

Hydrogen bonding increases the melting point.

Run a mixed-melting point experiment.

Compound A: 83-84 °C, Compound B: 81-82 °C

By the presence of dipole-dipole interactions or hydrogen bonding.

Intermolecular forces.

Mix some unknown compound in equal parts with some known compound and take the melting point of the mixture.