Indicators
are used everyday in labs to measure the pH of different substances. There
are many varieties of indicators that are used depending of the relevance
of their color scales (most have limited but accurate scales); however,
the universal indicator stands out among the others because of its wider
scale. Today’s lab investigates the use of red beets as a pH indicator.
An indicator is a compound that determines pH by detecting H+ protons. The indicator, when introduced to a substance may bond with the H+ or OH- ions, and the different electronic configurations provide the indicator with its final color.
In this lab we took a deep base and mixed it with our red beet indicator. The result was a deep purple solution. To demonstrate how indicators change color to show pH, we put dry ice in the solution. When dry ice sublimes it will make the solution it is in more acidic; therefore, over time, the color of our beet/base solution should change. We’ll see what happens!
One small caution: dry ice is dangerous. It is rather cold and can cause nasty burns. Please don't touch it barehanded. If you would like to do this lab at home (it is relatively safe) make sure to use proper equipment when handling the ice. Insulated oven gloves work nicely.
We started our lab by putting some red beets in boiling water. It took
a little while for the water to turn deep red (as it should)
so
we let it boil while we went to get some dry ice. Upon return we noticed
that the water was nice and red and we were ready to start with our experiment.
We put amounts of our indicator aside and then we prepared to mix it with
Windex. The proportions had to be decent because we had to make sure that
most of the change in color was a result of the indicator reacting with
the base, rather that the Windex just dying the solution. Play around until
you get it more or less right, and then proceed to the fun stuff!
Anyway to give you an idea of what the solution should l ook like when the proportions are right. Take a look at the following picture:
Once we
got the mixture right we cut a small piece of dry ice and we put it into
the beaker. This part is rather messy so we would advise that you do it
over a sink. When dry ice goes into a liquid it bubbles and creates a fog.
This is something most people have witnessed; however, if you haven’t
seen it in soapy water, you’re missing half the fun. In soapy water
it bubbles and said bubbles tend to overflow and go everywhere. This is
also the case with Windex, except for the bubbles probably aren’t
great for your skin, and are probably worse for your digestive tract!
Anyway, I digress. There should be noticeable changes in color after a few seconds. This should also be a sign that the proportions were done more or less correctly. We took a sequence of images to show you what we thought it should look like. The next three pictures are in chronological order left to right:
Finally when you are all done, make sure to have a beaker full of the original concoction and then after the mess is cleaned. Data can be collected and conclusions can be drawn.
Finally when we examine our final results we can see that our methods did in fact work. We started off with a purple/green mixture that meant that we had a strong base. Then after the dry ice was added the liquid became lighter and lighter until it stopped around orange or red. This means that we did in fact make the transition from base to acid. The before and after picture below is quite telling:
Cite
Our Experiments & Research
If you have used any of this information or any of these images
please go ahead and cite them in your bibliography. For your convenience,
this is what the citation would look like in MLA format:
Family, Afrooz. “Red Beet pH Meter.” May 09, 2005 Mad Physics. dd mmm. yyyy †
<http://www.madphysics.com/exp/red_beet_ph_meter.htm">
We are glad to share our knowledge with you as long as you cite all of our info, and contact us before you use anything for non-educational purposes (commercial, etc.).
† In the bibliography you must insert the day you visited the site (this is relevant because the site could change at some point), therefore, in the bibliography above replace dd with the day you visited, mmm with the abreviated month, and yyyy with the year (ex: dd mmm. yyyy becomes 23 Dec. 2004).
