Seltzer Produced a pH of 3.5 that turned the Juice Violet

Seltzer is a common name for carbonic acid, and carbonic acid is made when carbon dioxide is dissolved in water. The chemical reaction to make carbonic acid is printed below the violet cup with pH 3.5. Carbon dioxide plus water makes carbonic acid that in turns separates into hydrogen cations and a bicarbonate anions. Excess hydrogen cation make the solution acidic and turned the cabbage juice violet. Carbonic acid is consider harmless, in fact it is used to make the carbonated beverages sold for consumption. This organic acid is common and harmless.

Vinegar Produced a pH of 2.4 and turned the Juice Indigo

Vinegar contains acetic acid, a week organic acid, produced by fermenting bacteria on apple juice. Acetic acid kills the fermentation bacteria at 5% strength. Interestingly, there is a species of microorganism that can survive 5% acetic acid called Vinegar Eels or Turbratrix aceti. https://www.youtube.com/watch?v=7Vzp3CnrBpY Vinegar will in general disinfect items of bacteria because of its acidity. The figure below the indigo glass shows an acetic acid molecule combining with a water molecule to form acetate negative ion and a positive hydronium ion or acid. Only a small percentage of molecules turn into acid ions and that is why it is a weak acid.

Lemon Juice Produced a pH of 2 and Turned the Juice Pink.

Lemon juice turned the cabbage juice pink at about pH 2. Lemon juice contains citric acid, an organic acid, see chemical structure in picture. Lemon juice is weak enough to be eaten without harm, but can cause eye and skin irritation. The molecular structure for citric acid was placed next to the pH 2 display glass.
Note the structure has three acid groups (COOH). The reason this is not as strong as muriatic acid is because the COOH groups do not release all their hydrogens as H+, that determines the acid’s strength.

Muriatic acid, Scientifically Called Hydrochloric Acid, Produced a pH of 0 and Turned the Juice Bright Red

Muriatic
acid turned cabbage juice bright red and produced a pH of 0. Adult supervision is required when handling this chemical. Muriatic acid is the common name for hydrochloric acid, and given the formula of HCl. It is a strong acid cleaner used on masonry surfaces to clean stains. It can dissolve metals, biological matter like skin and eye, and some rock and cement. It can damage eyes and skin on contact, so gloves and safety glasses are needed. This solution contains 20% HCl. Our stomach acids contain 0.5% HCl and can dissolve flesh. If a chemical tests bright red to cabbage juice, it may be deadly acid

Household Chemicals Added to Cabbage Juice Produced a Range of pHs and Changed the Colors

About a teaspoon of the household chemicals in the background produced a pH in the cabbage juice from 0 (on the left) to 14 (on the right), the entire pH range. The pH produced was written on the glass. Acidic compounds turned the juice red in, neutrals stayed the purple color of the cabbage juice, and basic compounds turned to blue. The strong bases at pH 11 and 14 turned the juice green.

Red Cabbage Juice Made from Distilled Water Had a Purple Color

Purple cabbage juice was produced by blending red cabbage leaves with distilled water and filtering the mixture. The purple color indicated that the distilled water extract had a pH of about 6.5. Distilled water was slightly acidic, because it had absorbed carbon dioxide upon standing. The six cups of extract were parsed into eleven 4 oz plastic wine glasses. The juice in all 11 glasses maintained the same color until chemicals were added during the experiment.

Experimental Materials

The photo contains the supplies needed for the experiment. One hundred grams of cabbage leaves is taken from the head of cabbage and placed in a blender. Then, 6 cups of water is placed with the and the leaves blended for 5 minutes. The blended mixture is filtered a coffee filter leaving the cabbage leaves in the coffee filter supported by a strainer. The solution has enough volume to partially fill 12 plastic 5-oz wine glassed.

Shopping List for Experimental Materials

The cost for a class of 12 students would be increased by $24.00 for shot glasses and $11 dollars for measuring spoons making the new total $77.50. However, dividing by 12 students would make the cost about $7 per student, and that falls with a typical lab fee for the course. This is an example where purchasing in volume for a class make the experiment more affordable. Finally, the materials left over can be used in the home and not wasted. Using the acid afterward may be an issue.

Household Chemicals Used to Produce Standard pHs in Cabbage Juice

The 11 household chemicals pictured above will be individually added to cabbage juice and the color of the juice documented. These chemicals are considered standards, because the pH that it will produce in water has already been found and recorded in the chemistry literature. The known pH is written under each pictured container. The pH range is from 0 to 14, and these standards cover that complete range. Eleven transparent containers will be filled with cabbage juice and one by one the chemicals will be added to a single container. The color range will be recorded. Now, any chemical with an unknown pH can be added to produce a color and that color compared to the standards to determine the pH produced by the test sample.

What is an Acid or Base

Almost everyone knows the formula for water, H2O. Two H2O molecules are pictured on the left side of the equation above with the red balls representing an oxygen atoms and the white balls representing hydrogen atoms. But, did you know that water can break down into two particles, H+ and OH-. The H+ particle is called acid and the OH- is called base. The H+ however quickly attaches to another water molecule and exists as a H3O+. If the concentration of H3O+ and OH- are the same, then the water is pH balanced, non toxic. However, if H3O+ is greater than the OH-, then the water is said to be acidic. Chemicals added to water can turn water into poisonous acid or base solutions.

Red Cabbage Juice after Being Filtered through a Coffee FIlter

When the blender mix of chopped red cabbage leaves turn dark purple with time, the solution is filtered through a coffee filter in a strainer. The purple solution passes through the coffee filter and the leaves remain behind in the coffee filter. The liquid is dark purple and can be used for the experiment.

Cyanidin Extracted out of Red Cabbage Leaves at Room Temperature with Blender

A student extracts cyanidin out of the red cabbage leaves using a blender at room temperature. Purple cyanidin was readily water soluble. While many of extraction methods call for heating the chopped leaves in water, we found that chopping the leaves into fine pieces in a blender also increased the extraction without a heat source. Distilled water was used so that water impurities do not react with the cyanidin. The concentration of cyanidin in the water increased with time.

Cyanidin, Plant Polyphenol that Changes Color with pH

The common red cabbage plant as found in the local grocery store produces a chemical call cyanidin in its leaves.. The chemical structure shown is called a polyphenol, poly meaning “many” and phenol meaning it has “OH” groups. Many foods in a healthy diet contain high levels of naturally occurring phenols in fruits, vegetables, cereals, tea and coffee. Cyanidin has the formula of C15H11O6+. Cyanidin is also found in red berries. The chemical is easily extracted and changes color when in water with pH across the acid base scale, 0-14.

Why Have Students Study Cabbage Juice as an Acid-Base Indicator

Water is the most important chemical to us since we evolved out of water, are made of about 60% water, and need water to live. Water has the chemical formula of H2O, however water can break down into the ions of H+ and OH-. The amount of H+ in water is measured in units of pH that can range for 0 to 14. Pure water has a pH of 7. Animals can live in water between the pH of 4 to 10, outside that range, most living things die. Red cabbage juice changes color at different pHs and can be used to measure pH of water samples. This project will calibrate the cabbage juice color scheme against standards of know pH, and then use cabbage juice to test to quality of water under different conditions. With this experiment, the students will learn qualitative analytical chemistry.

Chemistry: Grades 2-4 Super Saturday Classes 01/11/20 – 02/22/20

Week 1: Make Cabbage Juice pH Indicator

Week 2: Make Bath Bombs

Week 3: Make Essential Oils and Aromatherapy

Week 4: Make Flavors and Home Made Ice Cream

Week 5: Make Glycerin Soap

Week 6: Make Lip Balm