Ethyl alcohol (ethanol), isopropyl alcohol (isopropanol), water, and acetone are all different substances often used as stain removers. In this assessment you will apply what you know about electrical forces between particles at the molecular scale to make inferences about how that might scale to determine properties like evaporation and freezing point. Ultimately, you will design and conduct an experiment for greater insight into how these substances act as solvents. 

A solvent is a substance that is used to dissolve (break apart the molecules of) other substances called solutes. Use the following table as a reference for measured boiling points and freezing points of the solvents you come across in this assessment.

List of boiling and freezing information of solvents

Rubbing alcohol has the chemical name isopropyl alcohol or isopropanol. It is great at getting in between molecules of nail polish or chemicals from stains, and breaking them up to make them easier to remove. 

In chemistry, an alcohol is an organic molecule that contains a hydroxyl group (an oxygen molecule bonded with hydrogen, written as -OH) bonded to a saturated carbon atom (this means the carbon atom is sharing its other electrons with hydrogen atoms). 

Ethyl alcohol or ethanol is another common alcohol. Ethanol is found in most of the gas we put in cars, in cleaning products, and in alcoholic beverages like beer, wine, and liquor. 

Although alcohols like ethyl alcohol and isopropyl alcohol both work as stain removers, they have different chemical structures and properties.

Molecules that are harder to freeze (low freezing point) have weaker attractive forces between the protons in the nucleus and surrounding electrons of each of their atoms.

Molecules that are harder to freeze (low freezing point) have stronger attractive forces between the protons in the nucleus and surrounding electrons of each of their atoms

Molecules that are harder to freeze (low freezing point) have stronger attractive forces between molecules

Molecules that are harder to freeze (low freezing point) have weaker attractive forces between molecules

Q2 — Evaporating Isopropyl Alcohol (Isopropanol)

Isopropyl alcohol feels colder than water because the molecules are tightly bound to each other due to strong attraction forces. This leads to them evaporating more easily.

Isopropyl alcohol has weaker forces between molecules than water does. These relatively weaker forces cause isopropyl alcohol to have a lower boiling point and evaporate faster.

Water has stronger attractive forces within atoms because of the strong electronegativity of oxygen in water. This causes water to evaporate slower since its atoms do not degrade easily into hydrogen and oxygen. 

Water has weak attractive forces between molecules called hydrogen bonds. These bonds break easily which leads to more fluid movement of molecules and a higher boiling point than that of isopropyl alcohol. 

Acetone is not an alcohol but it is a great solvent. It is one of the most common ingredients in nail polish and nail polish remover.

If you leave an open bottle of acetone-based nail polish remover out it will evaporate faster than a glass of water. Based on what you know about electrical forces between particles, explain this phenomenon using a scientific model that includes a drawing and a claim, evidence, reasoning argument.

Some ideas for how to write your argument:

In my scientific model I drew ____. This represents how _____. I think my model is accurate because I know ____. Alternatively, record video or audio that explains the phenomenon. 

Water, isopropyl alcohol, ethyl alcohol, and acetone are all used as solvents, but which of these is the best stain remover? Well, because each substance has different properties this question doesn’t have a simple answer. It might be better to pose a more specific research question that we can answer by collecting some data. 

Using the investigation template and make a choice of very specific materials below. Write a research question, identify an independent and dependent variable, write a lab procedure and set up, identify constants, and collect data

What conclusions can you draw from your experimental data? 

Based on what you know about electrical forces between particles and how they affect properties of substances at the bulk scale, write a possible explanation for the results of your investigation.

What are some limitations of your investigation and results? What further evidence could you collect?

An assessment template in the style of the next generation science standards.

NGSS Assessment