S CIENCE F AIR P ROJECT 2008 Angela Slaughter December 17, 2008 Teacher: Ms. Slaughter

TITLE Which Citrus Fruit Has the Most Acid?

PROBLEM It is known that nutritional acids, such as Vitamin C, are found in different kinds of fruits. Citrus fruits are the most common acidic fruits. Some people however, do not like to eat fruits with too much acid in them. This experiment will determine which common citrus fruit has the most acid: regular oranges, lemons, limes, or grapefruits. This will be determined by measuring the acidity of each fruit. The citrus fruit with the highest acidity will be considered to be the fruit with the most acid. It is known that nutritional acids, such as Vitamin C, are found in different kinds of fruits. Citrus fruits are the most common acidic fruits. Some people however, do not like to eat fruits with too much acid in them. This experiment will determine which common citrus fruit has the most acid: regular oranges, lemons, limes, or grapefruits. This will be determined by measuring the acidity of each fruit. The citrus fruit with the highest acidity will be considered to be the fruit with the most acid.

H YPOTHESIS If the type of citrus fruit changes then the acidity of the citrus fruit will change. I think when the acidity of an orange, lemon, lime, and grapefruit are tested, and compared to one another, the lemon will have the highest acidity.

E XPERIMENT (M ATERIALS & P ROCEDURES ) MATERIALS Citrus Fruit 3 lemons 3 limes 3 oranges 3 grapefruits Litmus Paper (Acidic test Litmus paper or pH Litmus paper) 3 strips for each type of fruit Litmus Paper Scale Color Chart (usually provided with the Litmus paper) Knife for cutting the fruit in half Faucet or source of clean water used to rinse knife off after each fruit is cut in half to avoid contamination Roll of paper towels Solid work surface for experimentation (ex.: table or countertop) MATERIALS Citrus Fruit 3 lemons 3 limes 3 oranges 3 grapefruits Litmus Paper (Acidic test Litmus paper or pH Litmus paper) 3 strips for each type of fruit Litmus Paper Scale Color Chart (usually provided with the Litmus paper) Knife for cutting the fruit in half Faucet or source of clean water used to rinse knife off after each fruit is cut in half to avoid contamination Roll of paper towels Solid work surface for experimentation (ex.: table or countertop)

E XPERIMENT (M ATERIALS & P ROCEDURES ) PROCEDURES 1. Select one of the fruits and cut it in half using the knife. It doesn’t matter which type of fruit you start with. 2. Set both halves on the work surface with the skin side of the fruit touching the surface. Be sure not to let anything touch the fruit’s flesh to avoid any contamination. 3. Take one strip of Litmus paper and touch it to the flesh of the fruit for about 2 seconds, just long enough for the fruit’s juices to soak into the Litmus paper strip. 4. The Litmus paper containing the fruit’s juice will begin to change colors. Wait until you observe that the paper has stopped changing colors. PROCEDURES 1. Select one of the fruits and cut it in half using the knife. It doesn’t matter which type of fruit you start with. 2. Set both halves on the work surface with the skin side of the fruit touching the surface. Be sure not to let anything touch the fruit’s flesh to avoid any contamination. 3. Take one strip of Litmus paper and touch it to the flesh of the fruit for about 2 seconds, just long enough for the fruit’s juices to soak into the Litmus paper strip. 4. The Litmus paper containing the fruit’s juice will begin to change colors. Wait until you observe that the paper has stopped changing colors.

E XPERIMENT (M ATERIALS & P ROCEDURES ) PROCEDURES 5. Once the Litmus paper has reached its final color, compare it to the colors on the scale color chart. The color of the Litmus paper containing the fruit juice should closely match one of the colors on the scale. 6. Record the number associated with the matching color. This number corresponds to the acidity level of the fruit tested. 7. Rinse or wash the knife to get rid of any juice from the fruit that was just cut. 8. Wipe the knife dry with a paper towel. 9. Dispose of BOTH halves of the fruit AND the paper towel used to dry the knife. 10. Repeat this process 3 times for each type of fruit. Use a different fruit each time you test. PROCEDURES 5. Once the Litmus paper has reached its final color, compare it to the colors on the scale color chart. The color of the Litmus paper containing the fruit juice should closely match one of the colors on the scale. 6. Record the number associated with the matching color. This number corresponds to the acidity level of the fruit tested. 7. Rinse or wash the knife to get rid of any juice from the fruit that was just cut. 8. Wipe the knife dry with a paper towel. 9. Dispose of BOTH halves of the fruit AND the paper towel used to dry the knife. 10. Repeat this process 3 times for each type of fruit. Use a different fruit each time you test.

D ATA Citrus Fruit pH Trial 1 pH Trial 2 pH Trial 3 Average pH LIME GRAPEFRUIT ORANGE4444 LEMON pH SCALE = 1 – 14 LOWER pH = MORE ACID HIGHER pH = LESS ACID

D ATA

R ESULTS According to the data collected, the lemon has the lowest pH at an average of 1.83, which means its juice is the most acidic. The average pH of the orange is 4, 3.67 for the grapefruit, and 2.17 for the lime. The pH of the orange and the grapefruit are fairly close to each other. Likewise, the pH of the lemon and lime are close. According to the data collected, the lemon has the lowest pH at an average of 1.83, which means its juice is the most acidic. The average pH of the orange is 4, 3.67 for the grapefruit, and 2.17 for the lime. The pH of the orange and the grapefruit are fairly close to each other. Likewise, the pH of the lemon and lime are close.

C ONCLUSION The pH of each fruit was measured three different times. Each measurement was taken from a separate piece of fruit, not the same fruit each time. The average pH of those measurements was taken into account to form the concluding statement. When the pH of the juice of a lime, grapefruit, orange, and lemon was measured, the lemon had the lowest average pH of This indicates that the lemon also has the most acid because the lower the pH, the more acidic a substance is. These findings support my original hypothesis that the lemon would have the most acid. In the future, I would like to study further the nutritional or health benefits of eating too much, or too little, acidic fruits. I am also curious about finding out some of the risks that may be involved in consuming too much acidic fruit. For example, I have been told that acidic fruit, especially citrus fruits which tend to be highly acidic, can ruin tooth enamel. I believe that healthy teeth are very important so this could be simply one of the concerns I may want to investigate further.