Red Cabbage Juice Usage to Test for Acids and Bases

From the definition that used to be made by a chemist named Svante Arrthenius, for a substance to qualify as an acid, it must have the potential to release a hydrogen ion or a proton. If this substance is dissolved in water, there is a shift in balance between the hydrogen ions and the hydroxide ions consequently there will be less hydroxide ions than hydrogen ions in the resultant solution, making it acidic. On the other hand, a base (sometimes referred to as an alkaline) need to have the ability to release a hydroxide ion (Hydrogen and oxygen compound ion). Alternatively, a base can be defined as any substance that can accept hydrogen ions. When such a substance is dissolved in water there is an opposite shift in the balance between the hydroxide ions and hydrogen ions. Due to the fact that bases take in hydrogen ions, the resultant solution contains less hydrogen ions than hydroxide ions hence making it alkaline.

The distinction between acids and bases all lies in the differences in the Hydrogen ions (these are usually abbreviated as the symbol H+ in chemistry). In some substances, such as water, there is a small number of molecules that split up. From these water molecules, some lose a positively charged ion (Hydrogen ion) and are turned into hydroxide ions (abbreviated as the chemical symbol OH-). The hydrogen ions that are lost are combined with molecules of water to make a different type of ions known as hydronium ions (abbreviated as the chemical symbol H3O+). For the sake of keeping things simple, hydronium ions are synonymous with hydrogen ions (H+). When water is pure, the number of hydroxide ions it contains is equal to that of hydrogen ions. The resultant solution neither exhibits acidic nor basic properties.

Alkalinity and Acidity are usually measured using a scale called pH which is logarithmic in nature. The reason for this is because when a solution is strongly acidic, it can contain more ions of hydrogen than those in a concentrated base by over one hundred trillion (100,000,000,000,000) times. On the other hand, when a solution is a concentrated base, it can contain more hydroxide ions than those in a concentrated acid by more than one hundred trillion (100,000,000,000,000) times. In common solutions that we interact with every day, the concentrations of hydrogen and hydroxide ions can vary over the range given above.

To reduce the difficulty of dealing with numbers as large as these, a logarithmic scale known as the pH scale was adopted by scientists. In this scale, every change that occurs on one unit of the pH scale equates to a change ten times over in the concentration of hydrogen ions. Theoretically, he pH scale is open-ended although most values of solutions fall between 0 and 14.

We study these substances in order to be able identify them when we encounter them, understand their properties and be able to utilize them in the different chemical processes that take place in our day to day lives. There exist different high accuracy methods that can be used to detect the presence of these acids and bases. Most of these methods are carried out under laboratory conditions and are difficult to carry out at home. How then can we detect these acids and bases in homes without having to carry samples of substances to labs?

The importance of acids and bases varies across several processes that take place in the realm of chemistry. The presence of acids in the human stomachs aids in the process of digestion of the food ingested by humans, the absence of which causes several issues such as bloating and indigestion. Bases on the other hand are commonly used in cleaning solutions such a soap, detergent and shampoo. A balance of acidity and alkalinity is essential for the survival of underwater ecosystems.

Hypothesis

The main aim of this experiment is to test for acids and bases using juice obtained from the leaves of red cabbages. It is assumed that the juice changes color according to the pH levels of the substance it is exposed to. The colors that the juice ranging from red / bright pink, for very acidic substances to greenish yellow for the alkaline substances (bases).

Materials Used

The materials that were used in this experiment include:

• Red Cabbage
• Coffee Filters
• Different household substances of known pH

Procedure

pH Paper Creation

This procedure mainly involved the creation of pH paper strips from red cabbage juice and coffee filter and this was done through the steps described below; 4 leaves were peeled off from the red cabbage; The red cabbage leaves were torn into small pieces, and the small pieces were placed on a microwave dish; The red cabbage leaf pieces were microwaved for 1 and a half minutes; The red cabbage leaf pieces were allowed to cool; Using a coffee filter, the red cabbage leaf pieces were patted until the filter was saturated with juice from the cabbage leaf pieces which was light purple in color; The filter was left to dry; The coffee filter was then cut up into strips that formed the pH paper.

Testing of the different pH levels of several substances involved dipping one of the homemade pH paper strips into the substance for 10 seconds and then observing the change of color exhibited by the paper.

Observations

pH Scale Creation

Harmful chemicals were avoided during the creation of the pH scale and thus the substances that were used have pH values that fall in the range of 2 to 12. One strip of the homemade pH paper was used per substance to see how the colors vary for each pH value on the scale. It was observed that acids turned the strips to different shades of pink yet bases (alkaline substances) turned the strips to different shades of green and/or blue. The indicator that was used for these tests is as follows; pH 2 – red / bright pink; pH 4 – light pink / purple; pH 6 – violet; pH 8 – blue; pH 10 – blue-green; pH 12 – greenish yellow.

The substances with known pH values that were used in the creation of the pH scale include; pH 2 – Lemon juice; pH 3 – Vinegar; pH 4 – Tomato juice; pH 5 – Black coffee; pH 6 – Cow’s milk; pH 7 – Dawn dish soap; pH 8 – Salt water solution; pH 9 – Baking soda solution; pH 10 – Toothpaste; pH 11 – Furniture cleaner, pH 12 – Soapy water.

Results (Data)

5 other substances whose pH values are known in theory were used to test for the indication shown by the homemade pH paper strips and these were; Coke Soda, Urine, Beer, Household Ammonia, and Shampoo. The results of the tests are shown below:

Table 1: pH Value Tests for Other Substances

Conclusion

From the results and observations that were made above, it is evident that the proposed hypothesis is true since the pH paper strips that were saturated with red cabbage juice changed colors with according to the different pH levels of the substances that they were exposed to. The pH values that were tested ranged from 2 to 12 and these were obtained from the colors of the homemade pH paper strips compared against the pH scale that was created.

One of the things that was learned from this experiment is that red cabbage juice can reliably be used to test for pH values of different substances. This can be very useful in real-life during processes such as mixing of homemade cleaning products as well as remedies for different ailments among humans and animals.

During this experiment, there could have occurred some errors that could have been brought about by several scenarios such as color blindness of the person conducting the experiment, contamination of the coffee strips with a biasing acid or base before it was saturated with red cabbage juice and usage of diluted substances that could have given wrong pH values.