Science Buddies: "Ask an Expert"

Can you measure surface tension with capillarity tubes?

Hi cameronh740,
Welcome to the Ask an Expert forums.
Yes, you can measure surface tension with capillary tubes. If you type "surface tension capillary tube" into a internet search engine like Google, you will find many pages that give the exact equation to calculate the surface tension. If you have any other questions about this, please let us know.
Chris

So If you measure the height of the water inside the capillary tubes that will tell how strong the surface tension because I don't understand the equasions and I am not going that in depth with my experiment.

So If you measure the height of the water inside the capillary tubes that will tell how strong the surface tension.

No and yes. Without understanding the equations so you can do the math, you can't come up with a surface tension measurement in scientific uints.

If you utilize the same capillary tube to measure the capillary height of two different liquids, you can make a statement about which liquid exhibits the weaker(stronger) surface tension. Because the equations are non-linear with respect to height, you can't even quantify the difference in surface tension (twice the height does not mean twice the surface tension).

If testing your hypothesis only requires comparing surface tension with a simple stronger / weaker relationship, then capillary tubes without dealing with the equations and math is sufficient. If not, then you are going to have to learn about these equations and do some math. That isn't a bad thing. We will be glad to help.

Does it matter how much water you put in the glass to measure the surface tension with capillary tubes?

Does it matter how much water you put in the glass to measure the surface tension with capillary tubes?

Yes and no. If you don't put in enough water so that the capillary tube has a fluid height below the surface of at least two tube diameters, you can end up with a small downward capillary force that alters the behavior slightly. Once you have at least 2 diameters worth of depth, it doesn't matter how much more water is in the glass.

I conducted my project and it came out to be that vinegar affected the surface tension of water the most but i do not know why this occurred. Can someone please help me?

I merged your new topic about this project with your old topic. Please keep future posts related to your project in the same topic by using the "post reply button." Thanks!
This page has a brief discussion of the effects of different solutes on surface tension
http://en.wikipedia.org/wiki/Surface_te ... centration
You can find more information by typing "surface tension solutes" into an internet search engine like google.com.

If you would like more specific assistance with your experiment, we will need more information. For example, what other solutes did you test, and what procedure did you use to test them?

Looking forward to hearing more.

Chris

Well I tested salt sugar saop dirt and vinegar. I measured them i a capillary tube and I wanted two know why the vinegar affected the hieght that the water reached in the capillary. The vinegar made the water rise the highest against any other chemical by at least three eighths of and inch.

There are lots of factors that affect surface tension. When you disolve something in water (salt and sugar), you are changing the specific gravity (density) of the liquid. The more salt or sugar you add, the more you change the specific gravity. When you dilute something in water (vinegar), you are also changing the specific gravity (density) of the liquid.

In the case of dirt, you probably have a suspension and not a solution. The physics of suspensions and solutions are significantly different.

If you tested various concentrations of salt water and sugar water and vinegar, I would expect to you to find different column heights for different concentrations. It isn't fair to draw conclusions between different liquids that have different specific gravities.

Without knowing what your concentrations were or some other way to know what the specific gravity was, I really can't be of any help.

Note: There are other factors beyond specific gravity, viscosity for example that affect suface tension. Most soaps have a surfactant that is designed to reduce surface tension so that soap can easily be rinsed off of things, yet another factor.