The Freezing Point Depression

In my Current Topics class recently, we have been preparing a demonstration of a scientific topic and a lab activity that can go along with it. My group’s topic is the freezing point depression. It may not sound that complicated, and it is actually is rather simple, although it took much discussion, arguing, and questioning to figure out exactly how the freezing point depression works. This has been a topic of interest for my group over the past couple of weeks and turned out to be quite fascinating.

Depressing the freezing point or melting point of a substance, since the temperature below which a substance freezes and above which a substance melts is the same, simply refers to the process of lowering the temperature at which a solid can melt into a liquid. This can be done with the addition of salt. We found a fun experiment to do, which was the “Ice Cream Lab”, which was supposed to demonstrate the freezing point depression. Although it took us a while to figure out how it was being exemplified in the experiment, eventually we came to a conclusion. Basically, the ice cream ingredients are put in a bag that is placed inside a larger bag containing a salt and ice mixture. The salt allows the ice to remain at its normal temperature (below 0°C), but melt into its liquid form. This salt and ice brine that surrounds the ice cream ingredients allows the cream to freeze properly and uniformly, therefore, helping in the process of making homemade ice cream.

Even though we liked this lab activity, we thought that it was very important to see if and how this principle could relate to the real world and be applied to our daily lives. We researched and discovered that salt is put on roads in the winter season for the same purpose, and based on the same principle. Since Winnipeg is very cold, snowy, and icy, for at least 4 months of the year, the use of salt on the roads in very significant to daily life in the city. When the salt is put on the ice in winter, it lowers the melting point of the ice, so that the ice is able to melt into liquid water and run off the roads. Because the roads in Winnipeg get so icy and slippery in the winter and create dangerous driving conditions, the principle of the freezing point depression is essential for keeping the people out of hazardous situations.

I think asking and being critical of why something is happening is important to growing and understanding how the world works. We decided that in order to continue with this lab, we needed to understand why salt was able to depress the freezing point of ice. The answer has to do with the structure of water at a molecular level. Water is made up of H₂O molecules, and the positively charged hydrogen atoms of the water molecules are attracted to the negatively charged oxygen atoms of other water molecules, in a process called hydrogen bonding. In liquid water, because there is more heat energy, the molecules are able to move faster and flow past each other more easily. Similarly, as the temperature of water decreases, the rate of movement of the H₂O molecules is slowed down. Because of this reduction in speed of the moving molecules, the positive hydrogen atoms and negative oxygen atoms bond more firmly to one another and create a crystallized structure (ice). In simpler words, when salt is added to ice water, the salt particles disrupt the bonding process of the water molecules, allowing the substance to remain in liquid form at a temperature where it would normally be a solid. Because of the addition of salt, the molecules that would normally attract each other and bond firmly together at temperatures below 0°C, are interrupted in the process, decreasing the number of bonds formed and therefore, keeping the liquid from entering into a solid state.

I hope you learned something new about how salt can be used to depress the melting point or freezing point of a substance. If you are looking for an experiment that deals with the freezing point depression, an ice cream lab is a fun way to learn about it! Here is a link to one possible ice cream lab you could perform to become more knowledgeable on the subject and see the freezing point depression in action: http://www2.waterforduhs.k12.wi.us/staffweb/smith/Nancy/chemistry/ice%20cream%20lab.htm

Thank you.

Gender Stereotypes: Effect on Performance?

I read an article that talked about gender stereotyping and the effects that it can have on people, particularly women. It is scientifically proven that women tend not to score as high as men on standard tests in some areas of science or mathematics. Women are also under-represented in science related professions, such as computer science and engineering.

Gender stereotyping, for example, “women are not good in science”, may actually interfere with the ability of women to perform well in science related examinations. For example, women might fear that the gender stereotype could be valid, and that it could possibly apply to them. This kind of negative thinking and the feeling of pressure associated with it could actually cause women to perform worse on science or math related tests.

This study that was described in the article used a psychological intervention called “values affirmation” to try to reduce the achievement gap between men and women in a college physics class. The values affirmation intervention involved having the students write about the importance of personally important values, such as friends and family, for fifteen minutes on two occasions during the course. The idea behind the intervention is that it helps women to more firmly establish a perception of personal integrity and worth, which in turn provides them with greater internal strength to cope effectively, including coping more effectively with the stresses of the course examination. The authors of the study found that the values affirmation intervention significantly improved the course performance of women who expressed a strong belief in the gender stereotype that men will do better in physics than women.

The remarkable thing about the study is that a very brief and pretty simple intervention, which was not even directly related to the course material, was able to a have a significant effect on women’s exam performance and subject mastery in physics. The results of the study also suggest that gender differences in performance in some science areas may reflect students’ expectations rather than their true underlying abilities.

I found this article and study particularly interesting because I am a strong believer in gender equality and breaking down stereotypes and generalizations. I find it fascinating that knowing how people think you will perform on an examination can affect the way your mind works, and the way in which you actually perform. I have always been an advocate for the equality of women and think stereotypes are not only offensive, but usually very inaccurate. Saying and believing things like “women are not as good at science and math” have actually been shown in this study to affect women’s performances, because they do not have full confidence in themselves that they can perform just as well as the men. I strongly believe that stereotyping is not only insulting and untrue for the most part, but that it actually can damage the way a person feels about themselves, and cause them to perform in the way they are expected to perform, rather than to the best of their ability.

The article is called “Reducing the Gender Achievement Gap in College Science: A Classroom Study of Values Affirmation”, and can be found at http://www.sciencemag.org.

Thank you!