So much of science is really about understanding and appreciating the beauty of nature, hence it seems strange to me how some people or companies (or both in the US since companies count as people now) paint the two as polar opposites. Though many of my previous posts have been a bit microbe-centric, I want to emphasize that the different scientific disciplines all relate to one another since science is about explaining nature, and nature does not fit into neat little compartments or categories.

Previously, I briefly covered the importance of microbes in nitrogen cycling for aquaponics systems, but a lot more than just nitrogen cycling is needed to keep plants healthy. Many plants also have a preferred soil pH, so it’s time to pay some respect to the study of chemistry!

If you’re an avid gardener, you probably already know that pH is a measure of acidity or alkalinity and that different plants grow better when rooted in soils of specific pH ranges. For example, blueberry bushes prefer slightly more acidic soils.

Many plants not only require a number of transition metal elements as nutrients (iron, copper, manganese to name a few), but also for these nutrients to be in a form that enables their uptake by the plant. For example, manganese is an important part of photosystem II in the photosynthetic reaction center, while copper is an important part of photosystem I. Love that plants take carbon dioxide and release oxygen? The manganese is important for that.

Simple photosynthesis overview
You probably already knew that Plants use water and carbon dioxide to produce energy and oxygen via photosynthesis
But did you know that manganese and copper play an important role in this process? This is one of several reasons Mn2+ is so important for plants

Plants are able take up manganese in its ionic form (Mn2+). In the soil, Mn2+ will often form salts with anions present in the soil, and many of these solid salts will be more soluble in acidic as opposed to alkaline conditions. This means that in acidic soil, the manganese may be more readily taken up by plants, which may help to explain why fruiting plants (in general) prefer a slightly acidic soil pH. Considering the amount of photosynthesis needed in order to synthesize all the sugars the sugars stored in the fruits. Copper and many other micronutrients are also more readily available in slightly acidic soils than they would be in alkaline soils.

And because chemistry is an awesome discipline that deserves a bit more love, here’s how to create your own pH indicator using red cabbage. It was one of the coolest experiments in the 7th grade science class, and may come in handy if you can’t afford a real pH testing kit for your aquarium.

Adapted from How to make Red Cabbage pH Indicator by Anne Marie Helmenstine, PhD.

Red cabbage contains a pigment molecule called flavin (an anthocyanin). This water-soluble pigment is also found in apple skin, plums, poppies, cornflowers, and grapes. Very acidic solutions will turn anthocyanin a red color. Neutral solutions result in a purplish color. Basic solutions appear in greenish-yellow. Therefore, it is possible to determine the pH of a solution based on the color it turns the anthocyanin pigments in red cabbage juice.

The color of the juice changes in response to changes in its hydrogen ion concentration. pH is the -log[H+]. Acids will donate hydrogen ions in an aqueous solution and have a low pH (pH 7).

Materials

  • red cabbage
  • blender or knife
  • boiling water
  • filter paper (coffee filters work well)
  • One large glass container

Procedure

  1. Chop the cabbage into small pieces until you have about 2 cups of chopped cabbage. Place the cabbage in a large beaker or other glass container and add boiling water to cover the cabbage. Allow at least ten minutes for the color to leach out of the cabbage. (Alternatively, you can place about 2 cups of cabbage in a blender, cover it with boiling water, and blend it.)
  2. Filter out the plant material to obtain a red-purple-bluish colored liquid. This liquid is at about pH 7. (The exact color you get depends on the pH of the water.)
  3. You can make your own pH paper strips using red cabbage indicator. Take filter paper (or coffee filter) and soak it in a concentrated red cabbage juice solution. After a few hours, remove the paper and allow it to dry (hang it by a clothespin or string). Cut the filter into strips and use them to test the pH of various solutions.

 
Red Cabbage pH Indicator Color Chart
pH – Color
2 – Red
4 – Purple
6 – Violet
8 – Blue
10 – Blue-Green
12 – Greenish Yellow

That’s it! Go forth and appreciate the wonders of acid-base chemistry. Visit http://chemistry.about.com for more awesome chemistry that can be done at home.

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