Here are three terms that relate to osmolarity, isotonic, hypotonic, and hyprotonic. The osmolarities of two solutions must be compared when using these terms. For example, our .1 molar NACL and .1 molar potassium fluoride isotonic will first determine the osmolarity of each solution and do this whenever asked to determine if solutions are isotonic, hypotonic, or hyprotonic to each other. So from the molarity of .1 NACL, we multiply the molarity of .1 times the number of ions in the formula, which is two, you get .2 osmolar for sodium chloride. And the same is for potassium fluoride, .1 molar times the 2 ion in the formula. And we see that the osmolarities of both solutions are equal, therefore these two solutions are isotonic to each other. Here is another example. Our .3 molar sodium chloride and .2 molar calcium nitrate isotonic. Again, determine the osmolarity of each solution first. For sodium chloride, it's .3 molar times the 2 ions in the formula. So the osmolarity is .6. For calcium nitrate, it's .2 molar times the 3 ions in the formula. There are two nitrates and one calcium. So the osmolarity is also .6. So these two solutions are isotonic to each other. When one solution is of lower osmolarity, that solution is considered to be hypotonic. For example, which solution if either is hypotonic, .2 molar sodium chloride or .1 molar potassium fluoride? As always, first determine the osmolarity of each. For sodium chloride, the osmolarity is .4. The two ions in the formula times the molarity of .2. It gives us .4 osmolar. The osmolarity of potassium fluoride is .1 molar times 2, which is .2 osmolar. So because potassium fluoride has the lower osmolarity, potassium fluoride is hypotonic to sodium chloride. Here's another example, which if either solution is hypotonic, .2 molar potassium fluoride or .2 molar methanol CH30H. The osmolarity of potassium fluoride is .4. The osmolarity of the methanol is .2. There are no ions in this formula. CH30H is a molecular or covalent compound. Therefore, no ions in the osmolarity is the same as the molarity. In this case, methanol is hypotonic to the potassium fluoride solution. One solution of the two is as a higher osmolarity, that solution is considered to be hypertonic. Now we'll do some examples asking which solution is hypertonic. We'll use the same solutions from the previous problem. Because sodium chloride has the higher osmolarity, sodium chloride is hypertonic to potassium fluoride. In the case of .2 molar potassium fluoride and .2 molar methanol, the potassium fluoride is hypertonic to the methanol solution. Here are two osmosis terms I want you to be familiar with. They apply to blood cells. The following video will illustrate these processes. The image on the left is human erythrocytes or red blood cells. The image on the right is enhanced with filters. These living cells are in isotonic solution, note a loss in shape. Now the solution has been changed to have a high salt concentration. It is hypertonic. The red blood cells travel and become crenated. Finally, the solution has been changed to plain water. The cells swell and burst, leaving empty memories behind. This phenomenon is called hemolosis.