With a pipette measure into a small beaker 2 cc. of lemon juice. Add 25 cc. of water and a few drops of phenolphthalein indicator. From the burette run in N/10 KOH solution until a faint pink tinge remains permanently. Note the number of cubic centimeters of KOH solution required to neutralize the citric acid in the lemon juice. Calculate the per cent of citric acid.
(1 cc. of N/10 KOH solution equals 0.00642 gm. citric acid. 1 cc. of H2O weighs 1 gm. Because of sugar and other matter in solution 1 cc. of lemon juice weighs approximately 1.03 gm.)
1. What is the characteristic acid of lemons? 2. What is the salt formed when the lemon juice is neutralized by the KOH solution? 3. Describe briefly the process for determining the acidity of lemon juice. 4. What per cent of acidity did you obtain? 5. How does this compare with the acidity of vinegar?
Experiment No. 6
Influence of Heat on Potato Starch Grains
With the point of a knife scrape slightly the surface of a raw potato and place a drop of the starchy juice upon the microscopical slide. Cover with cover glass and examine under the microscope.
In the evaporating dish cook a small piece of potato, then place a very small portion upon the slide, and examine with the microscope.
Make drawings of the starch grains in raw and in cooked potatoes.