Red Cabbage Juice And The Universal Indicator example essay topic

Will GodfreyChemistryMiss. Morrison May 21, 2000 Natural Indicators Each year millions of tourists travel to the woods of New England, upstate New York, Wisconsin, and Canada to witness the appearance of brilliant autumn colors. Sugar maples, red oaks, sumac, birch and other trees and shrubs turn from green to bright red, orange, and yellow. The short, cool days of autumn bring an end to the production of chlorophyll (the green light-gathering pigment). As chlorophyll gradually breaks down, the colors of the more stable carotenoid (yellow / orange ) and anthocyanin (red / blue /purple) pigments become visible.

Some years the leaves of a particular species are bright yellow, while other years they may appear redder or even purple. Although no one can accurately predict the timing or coloration of each year's show, we do know that there is a chemical basis for it. Anthocyanins (Figure I) are responsible not only for the red and purplish colors of autumn, but also for similar colors in various summer leaves (red cabbage, red lettuce, red plum tree), flowers (roses, hydrangeas, geraniums, bachelor buttons, dark pansies), fruit (cherries, red apples, grapes, tomato, blackberry, blueberry, plum), roots (beets, radishes), bulbs (red onions), and petioles (rhubarb). Anthocyanins are water-soluble and are dissolved in the cell sap rather than bound to the membranes as chlorophyll is. If cell sap in a leaf is very acidic, then anthocyanin's make the leaves a bright red color, but if it is less acidic the color may appear purple. The color of anthocyanin depends on acidity, and thus it may serve as a pH (acid / base ) indicator (Figure II). pH is a quantitative measure of the acidity or basicity of solutions.

Numerically, the pH of a solution is defined as the negative logarithm (base 10) of the ion (H 3 O+) concentration. If the pH is less than 7 the solution is acidic, if it is greater than 7 the solution is basic, and if it is 7 the solution is neutral. The higher the pH, the more basic the solution, and the lower the pH, the more acidic the solution. Figure II illustrates the relationship between color and pH for anthocyanin pigments extracted from red cabbage or other sources.

Since anthocyanin's are found in all of the above named organic materials, they are all very useful natural indicators. Natural indicators are better for detecting acids and bases than man made indicators. This experiment utilizes red cabbage juice, red onion juice, blueberry juice, phenolphthalein, blue, and universal indicator for the indicators and for the acids and bases, uses. 5 M hydrochloric acid, vinegar, water, ammonia, and. 5 M NaOH. Also for this experiment goggles, lab apron, wax pencil, two 20-well well-plate, 11 pipettes, and one sheet of white paper are needed.

This experiment, if done correctly, should show which type of indicator is more accurate. The procedures for this experiment are as follows: 1. Put on goggles and lab apron. 2.

Label the well-plates, A and B. 3. In the first column on well-plate A put 20 drops of red cabbage juice with a pipette and in the first well on well-plate B. Discard pipette. DO NOT reuse pipettes 4. In the second column on well-plate A put 20 drops of red onion juice with a pipette and in the second well on well-plate B. Discard pipette. 5. In the third column on well-plate A put 20 drops of blueberry juice with a pipette and in third well on well-plate B. Discard pipette.

6. In the forth column on well-plate A put 20 drops of blue with a pipette and in the forth well on well-plate B. Discard pipette. 7. In the fifth column on well-plate A put 20 drops of phenolphthalein with a pipette and in fifth well on well-plate B. Discard pipette. 8. In the sixth column on well-plate A put 20 drops of universal indicator with a pipette and in sixth well on well-plate B. Discard pipette.

9. In the first row on well-plate A put 5 drops of. 5 M HCl with a pipette. Discard pipette.

10. In the second row on well-plate A put 5 drops of vinegar with a pipette. Discard pipette. 11. In the third row on well-plate A put 5 drops of water with a pipette. Discard pipette.

12. In the forth row on well-plate A put 5 drops of ammonia with a pipette. Discard pipette. 13.5 M NaOH with a pipette. Discard pipette. 14.

Record all observations in a table 15. Pour all liquids down the drain with a lot of water. Clean up lab area. Data: Red Cabbage Red Onions Blueberry Bromothyol Blue Phenol pht-hale in Universal.

5 M HCl Light Pink Pale Red Red Yellow Clear Pale Red Vinegar Pink Pale Red Red Yellow Clear Light Red Water Light Purple None Light Red Blue Clear Green Ammonia Lime Green No Odor Light Yellow Dark Green Dark Blue Reddish Pink Purple. 5 M NaOH Yellow No Odor Light Yellow Dark Green Dark Blue Pink Turquoise The red cabbage juice and the universal indicator showed the widest range of color. Figure shows the different colors of red cabbage juice at the different pH levels. Red cabbage changes colors at a wide range pH levels because it contains a mixture of different anthocyanin's and other pigments. Universal indicator is man made with 0.05% of each of the following: methyl red, methyl yellow, thymol blue, and blue in ethanol. Figure IV shows the colors of Universal indicator different pH levels.

Red cabbage is a natural Universal indicator. Natural indicators are better than any man-made indicator is a false statement. This is because red cabbage and universal indicator do almost the same thing. Also this lab shows that each indicator has specific pH levels that they work the best at. This experiment shows how important anthocyanin's are to the chemistry world and to the tourist business for certain parts of the country.