At the other extreme, a 10 M solution of NaOH would have a pH of 15. Numerical examples from Shipman, Wilson and Todd. In pure water, the molar concentration of H + ions is 10-7 M and the concentration of OH-ions is also 10-7 M.
In order to tell if a guava is ripe, squeeze it gently. If it gives under your fingers, its ripe. 2. Look for any blemishes on the guava. You want to try to select guavas that are blemish-free. Blemishes or bruises can mean the fruit is bad or will not taste good. 3. Check the color of the guava. Ripe guavas are those that have gone from bright green to a softer yellowish-green color. If you see a touch of pink on the fruit, it is in its prime. If you don't find any that are yellow, you can always buy green guava and wait for them to ripen.
Smell the fruit. According to the California Rare Fruit Growers, the aroma of the guava changes when it is ripe becoming musky, sweet and penetrating, so you should be able to smell it without having to put the fruit up to your nose. Ripe guavas can be stored in the refrigerator for two days. 2  Guavas purchased or picked when green and hard continue to ripen when kept at room temperature. 3  Place green guavas in a paper bag with a banana or apple for faster ripening.