Effects of Acids and Bases on Browning Apples

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Apples and other fruit will turn brown when they are cut and the enzyme contained in the fruit (tyrosinase) and other substances (iron-containing phenols) are exposed to oxygen in the air. The purpose of this chemistry laboratory exercise is to observe the effects of acids and bases on the rate of browning of apples when they are cut and the enzymes inside them are exposed to oxygen. A possible hypothesis for this experiment would be: Acidity (pH) of a surface treatment does not effect the rate of the enzymatic browning reaction of cut apples. The following materials are needed for this exercise: - Five slices of apple (or pear, banana, potato, or peach) - Five plastic cups or other clear containers - Vinegar (or dilute acetic acid) - Lemon juice - Solution of baking soda (sodium bicarbonate) and water (you want to dissolve the baking soda. Make the solution by adding water to your baking soda until it dissolves.) - Solution of milk of magnesia and water (ratio isn't particularly important - you could make a mixture of one part water one part milk of magnesia. You just want the milk of magnesia to flow more readily.) - Water - Graduated cylinder or measuring cups Procedure 1. Label the cups: Vinegar Lemon Juice Baking Soda Solution Milk of Magnesia Solution Water 2. Add a slice of apple to each cup. 3. Pour 50 ml or 1/4 cup of a substance over the apple in its labeled cup. You may want to swirl the liquid around the cup to make sure the apple slice is completely coated. 4. Make note of the appearance of the apple slices immediately following treatment. 5. Set aside the apple slices for a day. Data 1. Observe the apple slices and record your observations. It may be helpful to make a table listing the apple slice treatment in one column and the appearance of the

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