Chemistry Lab Report Example

Hexane (C6H14) evaporates faster.

Look at the structure of this substance and contrast it to the structures of all of the other substances.

What do you discern about the structure of this molecule that is different or unique?

It lacks Oxygen in its structure whereas the rest of the structures contain Oxygen.

Use this observation to claim the connection between the structure, the strength of its IMFs and its rate of evaporation.

Which substance evaporated the slowest?

H2O evaporated the slowest

Look at the structure of this substance and contrast it to the structures of the remaining substances.

What do you discern about the structure of this molecule that is different or unique?

H2O has no Carbon in its structure. It has fewer hydrogen ions compared to the other structures. H2o compound also has the least number of bonds.

Use this observation to claim the connection between the structure, the strength of its IMFs and its rate of evaporation.

Water has a powerful Hydrogen bonding because it has two Hydrogen atoms bonded to one Oxygen atom. The resulting structure, i.e., H2O has incredibly solid Hydrogen Bonds to other H2O structures. The rate of evaporation is rather slow since it takes quite a lot of energy to break these strong IMFs that hold the substance together.

Study the structures of the remaining four substances. What do you see that all of the substances have in common? What do you see that is different about each of them? Use the table below to organize the thoughts.

Similarities of all four substances

All four possess Carbon, Hydrogen, and Oxygen in their structures

Unique Characteristics of Each Substance

Substance

(ranked from slowest to fastest evaporation) Characteristic related to its structure

D Has a decentralized electronegativity point

C Has a centralized alcohol group

B It has only two Carbons

A It has only one Carbon

Using the observations youve made in the table above, claim the connection between the structures, the strength of its IMFs, and its rate of evaporation.

The power of hydrogen bonding decreases relative to increase in a compounds molecular weight. Evaporation for the alcohols occurs relative to molecular weight, with compound A (Methanol, with the lightest molecular weight) evaporating first and compound D (1-Propane, the heaviest molecular weight) being the slowest at evaporating.

In the molecules below, show where the attractions (IMFs) are between the two water molecules. Be strategic about where you place them.

Intermolecular Forces (Hydrogen bonding)

Why did you place the forces where you did?

The primary intermolecular force present in water is the Hydrogen bond which occurs due to the strong dipole-dipole force. This force occurs when polar molecules attract one another. With oxygen being the electronegative pole and hydrogen the electropositive pole the hydrogen bond will be between these two.

Bellow are two hexane molecules. Draw in where you would predict the IMFs to be.

H H H H H HH - C - C - C - C - C - C - H

H H H H H HLondon Dispersion forces

H H H H H HH - C - C - C - C - C - C - H

H H H H H HWhy did you draw them there? How would you say these forces are different than the ones you drew between the water molecules in question 7?

Hexane is an Alkane that has a considerable chain length which gives it a large surface area. Hydrocarbons such as Hexane bind together through London dispersion forces that rely on surface area.

Unlike hydrogen bonds, London Dispersion Forces (LDF) occurs when a positively charged nucleus of an atom pulls the electron cloud of another atom. These LDF forces exist between a variety of molecules including polar, non-polar, ions, and noble gases, unlike Intermolecular forces that deal with molecules that have permanent dipole movements.

How do IMFs differ from chemical bonds (Intermolecular Forces)? Draw a picture to illustrate. Use water as an example.

Intramolecular Forces

H

HH

OOH

Intermolecular forces

How are IMFs similar to chemical bonds?

Both IMFs and chemical bonds are forces that act on molecules. The forces involve atoms coming together to form a more complex group structure that is far more stable than the atoms are individually and differs in terms of properties to the original elements. IMF and chemical bonds are exothermic, and the attractive force they have is courtesy of the pull of two opposite charges, i.e., positive and negative.

Use a CER to answer the question, How does the structure of the molecule affect the rate at which it evaporates?

Intermolecular forces and Hydrogen bonds have a bearing on the structure of any substance and as a result affect evaporation.

The strength of van der Waals forces is relative to the size of the atoms and molecules. Therefore, a large molecule has strong van der Waals attraction within its structure.

Intermolecular forces impact the boiling and melting points of substances thus, these attractions need more energy to break resulting in an effect on the rate of evaporation.